A Course Material on - Sasurie College of Engineering Sem 7/CS2060 H… · a course material on high speed networks by mr. m.shanmugharaj assistant professor ... cs2060 high speed

A Course Material on

HIGH SPEED NETWORKS

By

Mr. M.SHANMUGHARAJ

ASSISTANT PROFESSOR

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

SASURIE COLLEGE OF ENGINEERING

VIJAYAMANGALAM – 638 056

QUALITY CERTIFICATE

This is to certify that the e-course material

Subject Code : CS2060

Subject : HIGH SPEED NETWORKS

Class : IV Year ECE

being prepared by me and it meets the knowledge requirement of the university curriculum.

Signature of the Author

Name: M.Shanmugaraj

Designation: Assistant Professor

This is to certify that the course material being prepared by Mr.M.SHANMUGHARAJ is of adequate quality. He has referred more than five books among them minimum one is from abroad author.

Signature of HD

Name:Dr.K.Pandiarajan

SEAL

UNIT-1 HIGH SPEED NETWORKS 1-19

1.1 FRAME RELAY NETWORKS 1

1.2 STANDARD FRAME RELAY FRAME 1

1.3 CONGESTION-CONTROL MECHANISMS 2

1.4 FRAME RELAY VERSUS X.25 2

1.5 ASYNCHRONOUS TRANSFER MODE (ATM) 2

1.6 ATM PROTOCOL ARCHITECTURE 3

1.7 LOGICAL CONNECTION 4

1.7.1 CALL ESTABLISHMENT USING VPS 5

1.7.2 VIRTUAL CHANNEL CONNECTION USES 5

1.7.3 VP/VC CHARACTERISTICS 6

1.7.4 CONTROL SIGNALLING VCC 6

1.7.5 CONTROL SIGNALING VPC 6

1.8 STRUCTURE OF AN ATM CELL 6

1.8.1 GENERIC FLOW CONTROL 7

1.8.2 HEADER ERROR CONTROL 8

1.8.3 EFFECT OF ERROR IN CELL HEADER 9

1.9 ATM SERVICE CATEGORIES 10

1.10 ATM ADAPTION LAYER 11

1.11 HIGH-SPEED LANS 13

1.12 1.12 CSMA/CD 13

1.13 1.12.1 HUBS AND SWITCHES 14

1.14 1.14 FIBRE CHANNEL 16

1.14.1 I/O CHANNEL 17

1.15 1.15 WIRELESS LAN REQUIREMENTS 18

1.16 1.16 IEEE 802.11 SERVICES 18

UNIT-2 CONGESTION AND TRAFFIC MANAGEMENT 20-30

2.1 QUEING ANALYSIS 20

2.2 QUEING MODELS 20

2.3 SINGLE-SERVER QUEUE 21

2.4 MULTIPLE-SERVERS QUEUE 22

2.5. QUEUEING SYSTEM CLASSIFICATION 22

2.6 POISSON PROCESS 24

2.6.1 MATHEMATICAL FORMALIZATION OF LITTLE'S

THEOREM

24

2.7 EFFECTS OF CONGESTION 26

2.8 CONGESTION-CONTROL MECHANISMS 26

2.9.1 EXPLICIT CONGESTION SIGNALING 26

2.9 TRAFFIC MANAGEMENT IN CONGESTED NETWORK –

SOME CONSIDERATIONS

27

2.10 FRAME RELAY CONGESTION CONTROL 28

UNIT-3 TCP AND CONGESTION CONTROL 31-58

3.1 3.1 TCP FLOW CONTROL 31

3.2 TCP CONGESTION CONTROL 34

3.2.1 TCP FLOW AND CONGESTION CONTROL 35

3.3 RETRANSMISSION TIMER MANAGEMENT 35

3.4 EXPONENTIAL RTO BACKOFF 36

3.5 KARN’S ALGORITHM 36

3.6 WINDOW MANAGEMENT 36

3.7 PERFORMANCE OF TCP OVER ATM 39

3.8 TRAFFIC AND CONGESTION CONTROL IN ATM NETWORKS 41

3.9 REQUIREMENTS FOR ATM TRAFFIC AND CONGESTION

CONTROL

41

3.10 ATM TRAFFIC-RELATED ATTRIBUTES 43

3.11 TRAFFIC MANAGEMENT FRAMEWORK 45

3.12 TRAFFIC CONTROL 46

3.13 ABR TRAFFIC MANAGEMENT 51

3.14 RM CELL FORMAT 54

3.15 ABR CAPACITY ALLOCATION 54

3.15.1 COMPONENTS OF GFR MECHANISM 58

UNIT-4 INTEGRATED AND DIFFERENTIATED SERVICES 59-69

4.1 INTEGRATED SERVICES ARCHITECTURE (ISA) 60

4.2 ISA APPROACH 60

4.3 ISA COMPONENTS – BACKGROUND FUNCTIONS 61

4.4 ISA SERVICES 62

4.5 QUEUING DISCIPLINE 63

4.6 FAIR QUEUING (FQ) 63

4.7 GENERALIZED PROCESSOR SHARING (GPS) 64

4.8 WEIGHTED FAIR QUEUE 64

4.9 RANDOM EARLY DETECTION(RED) 65

4.10 DIFFERENTIATED SERVICES (DS) 66

UNIT -5 PROTOCOLS FOR QOS SUPPORT 70-80

5.1 RESOURCE RESERVATION PROTOCOL (RSVP) DESIGN GOALS 70

5.2 DATA FLOWS - SESSION 71

5.3 RSVP OPERATION 71

5.4 RSVP Protocol MECHANISMS 74

5.5 Multiprotocol Label Switching (MPLS) 74

5.6 MPLS OPERATION 76

5.7 MPLS PACKET FORWARDING 77

5.8 RTP ARCHITECTURE 80

5.9 RTP ARCHITECTURE DIAGRAM 80

CS2060 HIGH SPEED NETWORKS UNIT I HIGH SPEED NETWORKS 9 Frame Relay Networks – Asynchronous transfer mode – ATM Protocol Architecture, ATM logical Connection, ATM Cell – ATM Service Categories – AAL, High Speed LANs: Fast Ethernet, Gigabit Ethernet, Fiber Channel – Wireless LANs: applications, requirements – Architecture of 802.11 UNIT II CONGESTION AND TRAFFIC MANAGEMENT 8 Queuing Analysis- Queuing Models – Single Server Queues – Effects of Congestion – Congestion Control – Traffic Management – Congestion Control in Packet Switching Networks – Frame Relay Congestion Control. UNIT III TCP AND ATM CONGESTION CONTROL 11 TCP Flow control – TCP Congestion Control – Retransmission – Timer Management – Exponential RTO back off – KARN’s Algorithm – Window management – Performance of TCP over ATM. Traffic and Congestion control in ATM – Requirements – Attributes –Traffic Management Frame work, Traffic Control – ABR traffic Management – ABR rate control, RM cell formats, ABR Capacity allocations – GFR traffic management. UNIT IV INTEGRATED AND DIFFERENTIATED SERVICES 8 Integrated Services Architecture – Approach, Components, Services- Queuing Discipline, FQ, PS, BRFQ, GPS, WFQ – Random Early Detection, Differentiated Services. UNIT V PROTOCOLS FOR QOS SUPPORT RSVP – Goals & Characteristics, Data Flow, RSVP operations, Protocol Mechanisms – Multiprotocol Label Switching – Operations, Label Stacking, Protocol details – RTP – Protocol Architecture, Data Transfer Protocol, RTCP.

TOTAL: 45 PERIODS TEXT BOOK 1. William Stallings, “HIGH SPEED NETWORKS AND INTERNET”, Pearson

Education, Second Edition, 2002.

REFERENCES 1. Warland, Pravin Varaiya, “High performance communication networks”, Second Edition, Jean Harcourt Asia Pvt. Ltd., , 2001. 2. Irvan Pepelnjk, Jim Guichard, Jeff Apcar, “MPLS and VPN architecture”, Cisco Press, Volume 1 and 2, 2003. 3. Abhijit S. Pandya, Ercan Sea, “ATM Technology for Broad Band Telecommunication Networks”, CRC Press, New York, 2004.

CS2060 HIGH SPEED NETWORKS

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Unit I

HIGH SPEED NETWORKS

1.1 FRAME RELAY NETWORKS Frame Relay often is described as a streamlined version of X.25, offering fewer of the robust capabilities, such as windowing and retransmission of last data that are offered in X.25. Frame Relay Devices Devices attached to a Frame Relay WAN fall into the following two general categories: • Data terminal equipment (DTE) • Data circuit-terminating equipment (DCE) DTEs generally are considered to be terminating equipment for a specific network and typically are located on the premises of a customer. In fact, they may be owned by the customer. Examples of DTE devices are terminals, personal computers, routers, and bridges. DCEs are carrier-owned internetworking devices. The purpose of DCE equipment is to provide clocking and switching services in a network, which are the devices that actually transmit data through the WAN. In most cases, these are packet switches. Figure 10-1 shows the relationship between the two categories of devices. 1.2 STANDARD FRAME RELAY FRAME Standard Frame Relay frames consist of the fields illustrated in Figure Figure Five Fields Comprise the Frame Relay Frame

Each frame relay PDU consists of the following fields:

1. Flag Field. The flag is used to perform high level data link synchronization which indicates the beginning and end of the frame with the unique pattern 01111110. To ensure that the 01111110 pattern does not appear somewhere inside the frame, bit stuffing and destuffing procedures are used.

2. Address Field. Each address field may occupy either octet 2 to 3, octet 2 to 4, or octet 2 to 5, depending on the range of the address in use. A two-octet address field comprising the EA=ADDRESS FIELD EXTENSION BITS and the C/R=COMMAND/RESPONSE BIT.

3. DLCI-Data Link Connection Identifier Bits. The DLCI serves to identify the virtual connection so that the receiving end knows which information connection a frame belongs to. Note that this DLCI has only local significance. A single physical channel can multiplex several different virtual connections.

4. FECN, BECN, DE bits. These bits report congestion: o FECN=Forward Explicit Congestion Notification bit o BECN=Backward Explicit Congestion Notification bit o DE=Discard Eligibility bit


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5. Information Field. A system parameter defines the maximum number of data bytes that a host can pack into a frame. Hosts may negotiate the actual maximum frame length at call set-up time. The standard specifies the maximum information field size (supportable by any network) as at least 262 octets. Since end-to-end protocols typically operate on the basis of larger information units, frame relay recommends that the network support the maximum value of at least 1600 octets in order to avoid the need for segmentation and reassembling by end-users.

Frame Check Sequence (FCS) Field. Since one cannot completely ignore the bit error-rate of the medium, each switching node needs to implement error detection to avoid wasting bandwidth due to the transmission of erred frames. The error detection mechanism used in frame relay uses the cyclic redundancy check (CRC) as its basis. 1.3 CONGESTION-CONTROL MECHANISMS Frame Relay reduces network overhead by implementing simple congestion-notification mechanisms rather than explicit, per-virtual-circuit flow control. Frame Relay typically is implemented on reliable network media, so data integrity is not sacrificed because flow control can be left to higher-layer protocols. Frame Relay implements two congestion-notification mechanisms: • Forward-explicit congestion notification (FECN) • Backward-explicit congestion notification (BECN) FECN and BECN each is controlled by a single bit contained in the Frame Relay frame header. The Frame Relay frame header also contains a Discard Eligibility (DE) bit, which is used to identify less important traffic that can be dropped during periods of congestion. 1.4 FRAME RELAY VERSUS X.25 The design of X.25 aimed to provide error-free delivery over links with high error-rates. Frame relay takes advantage of the new links with lower error-rates, enabling it to eliminate many of the services provided by X.25. The elimination of functions and fields, combined with digital links, enables frame relay to operate at speeds 20 times greater than X.25. X.25 specifies processing at layers 1, 2 and 3 of the OSI model, while frame relay operates at layers 1 and 2 only. This means that frame relay has significantly less processing to do at each node, which improves throughput by an order of magnitude. X.25 prepares and sends packets, while frame relay prepares and sends frames. X.25 packets contain several fields used for error and flow control, none of which frame relay needs. The frames in frame relay contain an expanded address field that enables frame relay nodes to direct frames to their destinations with minimal processing . X.25 has a fixed bandwidth available. It uses or wastes portions of its bandwidth as the load dictates. Frame relay can dynamically allocate bandwidth during call setup negotiation at both the physical and logical channel level. 1.5 ASYNCHRONOUS TRANSFER MODE (ATM) Asynchronous Transfer Mode (ATM) is an International Telecommunication Union-Telecommunications Standards Section (ITU-T) standard for cell relay wherein information for multiple service types, such as voice, video, or data, is conveyed in small, fixed-size cells. ATM networks are connection-oriented.


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ATM is a cell-switching and multiplexing technology that combines the benefits of circuit switching (guaranteed capacity and constant transmission delay) with those of packet switching (flexibility and efficiency for intermittent traffic). It provides scalable bandwidth from a few megabits per second (Mbps) to many gigabits per second (Gbps). Because of its asynchronous nature, ATM is more efficient than synchronous technologies, such as time-division multiplexing (TDM). With TDM, each user is assigned to a time slot, and no other station can send in that time slot. If a station has much data to send, it can send only when its time slot comes up, even if all other time slots are empty. However, if a station has nothing to transmit when its time slot comes up, the time slot is sent empty and is wasted. Because ATM is asynchronous, time slots are available on demand with information identifying the source of the transmission contained in the header of each ATM cell. ATM transfers information in fixed-size units called cells. Each cell consists of 53 octets, or bytes. The first 5 bytes contain cell-header information, and the remaining 48 contain the payload (user information). Small, fixed-length cells are well suited to transferring voice and video traffic because such traffic is intolerant of delays that result from having to wait for a large data packet to download, among other things. Figure illustrates the basic format of an ATM cell. Figure :An ATM Cell Consists of a Header and Payload Data

1.6 ATM PROTOCOL ARCHITECTURE ATM is almost similar to cell relay and packets witching using X.25and framerelay.like packet switching and frame relay,ATM involves the transfer of data in discrete pieces.also,like packet switching and frame relay ,ATM allows multiple logical connections to multiplexed over a single physical interface. in the case of ATM,the information flow on each logical connection is organised into fixed-size packets, called cells. ATM is a streamlined protocol with minimal error and flow control capabilities :this reduces the overhead of processing ATM cells and reduces the number of overhead bits required with each cell, thus enabling ATM to operate at high data rates.the use of fixed-size cells simplifies the processing required at each ATM node,again supporting the use of ATM at high data rates. The ATM architecture uses a logical model to describe the functionality that it supports. ATM functionality corresponds to the physical layer and part of the data link layer of the OSI reference model. . the protocol referencce model shown makes reference to three separate planes: user plane provides for user information transfer ,along with associated controls (e.g.,flow control ,error control). control plane performs call control and connection control functions.


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management plane includes plane management ,which performs management function related to a system as a whole and provides coordination between all the planes ,and layer management which performs management functions relating to resource and parameters residing in its protocol entities . The ATM reference model is composed of the following ATM layers: • Physical layer—Analogous to the physical layer of the OSI reference model, the ATM physical layer manages the medium-dependent transmission. • ATM layer—Combined with the ATM adaptation layer, the ATM layer is roughly analogous to the data link layer of the OSI reference model. The ATM layer is responsible for the simultaneous sharing of virtual circuits over a physical link (cell multiplexing) and passing cells through the ATM network (cell relay). To do this, it uses the VPI and VCI information in the header of each ATM cell. • ATM adaptation layer (AAL)—Combined with the ATM layer, the AAL is roughly analogous to the data link layer of the OSI model. The AAL is responsible for isolating higher-layer protocols from the details of the ATM processes. The adaptation layer prepares user data for conversion into cells and segments the data into 48-byte cell payloads. Finally, the higher layers residing above the AAL accept user data, arrange it into packets, and hand it to the AAL. Figure :illustrates the ATM reference model.

1.7 LOGICALCONNECTION

Virtual channel connections (VCC) Analogous to virtual circuit in X.25 Basic unit of switching Between two end users Full duplex Fixed size cells Data, user-network exchange (control) and network-network exchange (network

management and routing)


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Virtual path connection (VPC) Bundle of VCC with same end points

Simplified network architecture.. Increased network performance and reliability. Reduced processing. Short connection setup time.. Enhanced network services.

1.7.1 CALL ESTABLISHMENT USING VPS

1.7.2 VIRTUAL CHANNEL CONNECTION USES Between end users

End to end user data Control signals VPC provides overall capacity

VCC organization done by users Between end user and network

Control signaling Between network entities


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Network traffic management Routing

1.7.3 VP/VC CHARACTERISTICS Quality of service Switched and semi-permanent channel connections Call sequence integrity Traffic parameter negotiation and usage monitoring VPC only

Virtual channel identifier restriction within VPC

1.7.4 CONTROL SIGNALLING VCC Done on separate connection Semi-permanent VCC Meta-signaling channel

Used as permanent control signal channel User to network signaling virtual channel

For control signaling Used to set up VCCs to carry user data

User to user signaling virtual channel Within pre-established VPC Used by two end users without network intervention to establish and release

user to user VCC 1.7.5 CONTROL SIGNALING VPC Semi-permanent Customer controlled Network controlled

1.8 STRUCTURE OF AN ATM CELL An ATM cell consists of a 5 byte header and a 48 byte payload. The payload size of 48 bytes was a compromise between the needs of voice telephony and packet networks, obtained by a simple averaging of the US proposal of 64 bytes and European proposal of 32, said by some to be motivated by a European desire not to need echo-cancellers on national trunks. ATM defines two different cell formats: NNI (Network-network interface) and UNI (User-network interface). Most ATM links use UNI cell format.


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GFC = Generic Flow Control (4 bits) (default: 4-zero bits) VPI = Virtual Path Identifier (8 bits UNI) or (12 bits NNI) VCI = Virtual channel identifier (16 bits) PT = PayloadType(3 bits) CLP = Cell Loss Priority (1-bit) HEC = Header Error Correction (8-bit CRC, polynomial = X8 + X2 + X + 1)

The PT field is used to designate various special kinds of cells for Operation and Management (OAM) purposes, and to delineate packet boundaries in some AALs. Several of ATM's link protocols use the HEC field to drive a CRC-Based Framing algorithm, which allows the position of the ATM cells to be found with no overhead required beyond what is otherwise needed for header protection. The 8-bit CRC is used to correct single-bit header errors and detect multi-bit header errors. When multi-bit header errors are detected, the current and subsequent cells are dropped until a cell with no header errors is found. In a UNI cell the GFC field is reserved for a local flow control/submultiplexing system between users. This was intended to allow several terminals to share a single network connection, in the same way that two ISDN phones can share a single basic rate ISDN connection. All four GFC bits must be zero by default.The NNI cell format is almost identical to the UNI format, except that the 4-bit GFC field is re-allocated to the VPI field, extending the VPI to 12 bits. Thus, a single NNI ATM interconnection is capable of addressing almost 212 VPs of up to almost 216 VCs each (in practice some of the VP and VC numbers are reserved). 1.8.1 GENERIC FLOW CONTROL

Control traffic flow at user to network interface (UNI) to alleviate short term overload Two sets of procedures

Uncontrolled transmission Controlled transmission

Every connection either subject to flow control or not Subject to flow control


SCE 8 ECE

May be one group (A) default May be two groups (A and B)

Flow control is from subscriber to network Controlled by network side

Terminal equipment (TE) initializes two variables TRANSMIT flag to 1 GO_CNTR (credit counter) to 0

If TRANSMIT=1 cells on uncontrolled connection may be sent any time If TRANSMIT=0 no cells may be sent (on controlled or uncontrolled connections) If HALT received, TRANSMIT set to 0 and remains until NO_HALT If TRANSMIT=1 and no cell to transmit on any uncontrolled connection: If GO_CNTR>0, TE may send cell on controlled connection Cell marked as being on controlled connection GO_CNTR decremented If GO_CNTR=0, TE may not send on controlled connection TE sets GO_CNTR to GO_VALUE upon receiving SET signal Null signal has no effect

USE OF HALT

To limit effective data rate on ATM Should be cyclic To reduce data rate by half, HALT issued to be in effect 50% of time Done on regular pattern over lifetime of connection

1.8.2 HEADER ERROR CONTROL

8 bit error control field Calculated on remaining 32 bits of header Allows some error correction

Initialize condition, receiver error correction is default mode for single bit error

correction After cell is received, HEC calculation & comparison is performed. No error is detected, receiver remains error correction mode. If error is detected, it checks for single or multi bit error Mode is changed to detection mode. 622.08Mbps


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155.52Mbps 51.84Mbps 25.6Mbps Cell Based physical layer SDH based physical layer

1.8.3 EFFECT OF ERROR IN CELL HEADER


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1.9 ATM SERVICE CATEGORIES

Constant bit rate (CBR) Real time variable bit rate (rt-VBR)

Non-real time Non-real time variable bit rate (nrt-VBR) Available bit rate (ABR) Unspecified bit rate (UBR) Guaranteed frame rate (GFR)

Real Time Services: Constant bit rate (CBR)

It is used where Fixed data rate continuously available. Tight upper bound on transfer delay. Mostly used in Uncompressed audio and video. Examples.

a. Video conferencing. b. Interactive audio. c. A/V distribution and retrieval.

Real time variable bit rate (rt-VBR)

Time sensitive application. Tightly constrained delay and delay variation. rt-VBR applications transmit at a rate that varies with time.

Example : compressed video a. Produces varying sized image frames. b. Original (uncompressed) frame rate constant. c. So compressed data rate varies.

Can statistically multiplex connections

i.e., allows network more flexible. Non Real Time Services: Non-real time variable bit rate (nrt-VBR)

It is possible to characterize expected traffic flow. So that Improve QoS in loss and delay. End system specifies:.

a. Peak cell rate. b. Sustainable or average rate. c. Measure of how bursty traffic .

Unspecified bit rate (UBR)

May be additional capacity over and above that used by CBR and VBR traffic. a. Not all resources dedicated to CBR & VBR. b. Due to Bursty nature of VBR, less than committed capacity is used.

For application that can tolerate some cell loss or variable delays


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a. e.g. TCP based traffic. Cells forwarded on FIFO basis. Best efforts service.

i.e., no initial commitment is made to a UBR Source & no feedback concerning congestion is provided. Available bit rate (ABR)

Application using ABR specifies peak cell rate (PCR) and minimum cell rate

(MCR). Resources allocated to give at least MCR.. Spare capacity shared among all ARB sources. e.g. LAN interconnection.

Guaranteed frame rate (GFR)

Designed to support IP backbone sub networks. Better service than UBR for frame based traffic. Including IP and Ethernet.

Optimize handling of frame based traffic passing from LAN through router to ATM

backbone. Used by enterprise, carrier and ISP networks. Consolidation and extension of IP over WAN. ABR difficult to implement between routers over ATM network. GFR better alternative for traffic originating on Ethernet

a. Network aware of frame/packet boundaries. b. When congested, all cells from frame discarded. c. User was Guaranteed minimum capacity. d. Additional frames carried out if not congested.

1.10 ATM ADAPTION LAYER AAL layer is organized into 2 logical sub layers

1. Convergence sub layer 2. Segmentation and re-assembly sub layer


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Convergence sublayer (CS) Support for specific applications AAL user attaches at SAP

Segmentation and re-assembly sublayer (SAR) Packages and unpacks info received from CS into cells

Four types Type 1 Type 2 Type 3/4 Type 5

AAL TYPE 1 It is dealing with CBR source SAR packs the bits into cells for transmission and unpacks bits at reception. Block accompanied by sequence number so that error PDU’s (Protocol Data Unit) are

tracked. 4 bit SN field consists of a convergence sub layers indicator (CSI) bit & 3 bit Sequence

Count (SC) Sequence Number Field (SNF) is an error code for error detection and possibly

correction on the sequence number field. AAL TYPE 2 It deals with VBR It is used in Analog applications


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AAL TYPE 3\4 Connectionless – each block of data presented to SAR layer is tracked independently. Connected – possible to define multiple SAR logical connection over single ATM

connection Message mode – transfers framed data stream mode – service supports the transfer of low – speed continues data into low

delay requirements. AAL TYPE 5 Streamlined transport for connection oriented higher layer protocols To reduce protocol overhead. To reduce transmission overhead. To reduce adaptability to existing transport protocols.

1.11 HIGH-SPEED LANS Emergence of High-Speed LANs 2 Significant trends

Computing power of PCs continues to grow rapidly Network computing

Examples of requirements Centralized server farms Power workgroups High-speed local backbone

Classical Ethernet Bus topology LAN 10 Mbps CSMA/CD medium access control protocol 2 problems:

A transmission from any station can be received by all stations How to regulate transmission

Solution to First Problem Data transmitted in blocks called frames:

User data Frame header containing unique address of destination station

1.12 CSMA/CD Carrier Sense Multiple Access/ Carrier Detection If the medium is idle, transmit. If the medium is busy, continue to listen until the channel is idle, then transmit

immediately. If a collision is detected during transmission, immediately cease transmitting. After a collision, wait a random amount of time, then attempt to transmit again (repeat from

step 1).


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1.13 Medium Options at 10Mbps <data rate> <signaling method> <max length> 10Base5

10 Mbps 50-ohm coaxial cable bus Maximum segment length 500 meters

10Base-T Twisted pair, maximum length 100 meters Star topology (hub or multipoint repeater at centralpoint)

1.12.1 HUBS AND SWITCHES Hub Transmission from a station received by central hub and retransmitted on all outgoing lines Only one transmission at a time Bridge Frame handling done in software


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Analyze and forward one frame at a time Store-and-forward

Layer 2 Switch Frame handling done in hardware Multiple data paths and can handle multiple frames at a time Can do cut-through Incoming frame switched to one outgoing line Many transmissions at same time

Layer 2 Switches Flat address space Broadcast storm Only one path between any 2 devices

Solution 1: subnetworks connected by routers Solution 2: layer 3 switching, packet-forwarding logic in hardware


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Benefits of 10 Gbps Ethernet over ATM No expensive, bandwidth consuming conversion between Ethernet packets and ATM

cells Network is Ethernet, end to end IP plus Ethernet offers QoS and traffic policing capabilities approach that of ATM Wide variety of standard optical interfaces for 10 Gbps Ethernet

1.14 FIBRE CHANNEL 2 methods of communication with processor:

I/O channel Network communications

Fibre channel combines both Simplicity and speed of channel communications Flexibility and interconnectivity of network communications


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1.14.1 I/O CHANNEL Hardware based, high-speed, short distance Direct point-to-point or multipoint communications link Data type qualifiers for routing payload Link-level constructs for individual I/O operations Protocol specific specifications to support e.g. SCSI

Fibre Channel Network-Oriented Facilities Full multiplexing between multiple destinations Peer-to-peer connectivity between any pair of ports Internetworking with other connection technologies

Fibre Channel Requirements Full duplex links with 2 fibres/link 100 Mbps – 800 Mbps


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Distances up to 10 km Small connectors high-capacity Greater connectivity than existing multidrop channels Broad availability Support for multiple cost/performance levels Support for multiple existing interface command sets Fibre Channel Protocol Architecture FC-0 Physical Media FC-1 Transmission Protocol FC-2 Framing Protocol FC-3 Common Services FC-4 Mapping

1.15 WIRELESS LAN REQUIREMENTS Throughput Number of nodes Connection to backbone Service area Battery power consumption Transmission robustness and security Collocated network operation License-free operation Handoff/roaming Dynamic configuration

1.16 IEEE 802.11 SERVICES Association Reassociation Disassociation Authentication Privacy


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Access Points – perform the wireless to wired bridging function between networks Wireless medium – means of moving frames from station to station Station – computing devices with wireless network interfaces Distribution System – backbone network used to relay frames between access points On wireless LAN, any station within radio range of other devices can transmit Any station within radio range can receive Authentication: Used to establish identity of stations to each other

Wired LANs assume access to physical connection conveys authority to connect to LAN

Not valid assumption for wireless LANs Connectivity achieved by having properly tuned antenna

Authentication service used to establish station identity 802.11 s upports several authentication schemes Range from relatively insecure handshaking to public-key encryption schemes 802.11 requires mutually acceptable, successful authentication before

association MAC layer covers three functional areas

Reliable data delivery Access control Security

Beyond our scope802.11 physical and MAC layers subject to unreliability

Noise, interference, and other propagation effects result in loss of frames

Even with error-correction codes, frames may not successfully be received

Can be dealt with at a higher layer, such as TCP However, retransmission timers at higher layers typically order of

seconds More efficient to deal with errors at the MAC level If noACK within short period of time, retransmit 802.11 includes frame exchange protocol Station receiving frame returns acknowledgment (ACK) frame Exchange treated as atomic unit Not interrupted by any other station


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Unit -02

CONGESTION AND TRAFFIC MANAGEMENT 2.1 QUEING ANALYSIS

In a queueing model is used to approximate a real queueing situation or system, so the queueing behaviour can be analysed mathematically. Queueing models allow a number of useful steady state performance measures to be determined, including:

the average number in the queue, or the system, the average time spent in the queue, or the system, the statistical distribution of those numbers or times, the probability the queue is full, or empty, and the probability of finding the system in a particular state.

These performance measures are important as issues or problems caused by queueing situations are often related to customer dissatisfaction with service or may be the root cause of economic losses in a business. Analysis of the relevant queueing models allows the cause of queueing issues to be identified and the impact of any changes that might be wanted to be assessed.

2.2 QUEING MODELS Queing models can be represented using Kendall's notation: A/B/S/K/N/Disc where:

A is the interarrival time distribution B is the service time distribution S is the number of servers K is the system capacity N is the calling population Disc is the service discipline assumed

Some standard notation for distributions (A or B) are: M for a Markovian (exponential) distribution Eκ for an Erlang distribution with κ phases D for Deterministic (constant) G for General distribution PH for a Phase-type distribution

Models Construction and analysis

Queueing models are generally constructed to represent the steady state of a queueing system, that is, the typical, long run or average state of the system. As a consequence, these are stochastic models that represent the probability that a queueing system will be found in a particular configuration or state. A general procedure for constructing and analysing such queueing models is:


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1. Identify the parameters of the system, such as the arrival rate, service time, Queue capacity, and perhaps draw a diagram of the system.

2. Identify the system states. (A state will generally represent the integer number of customers, people, jobs, calls, messages, etc. in the system and may or may not be limited.)

3. Draw a state transition diagram that represents the possible system states and identify the rates to enter and leave each state. This diagram is a representation of a Markov chain.

4. Because the state transition diagram represents the steady state situation between state there is a balanced flow between states so the probabilities of being in adjacent states can be related mathematically in terms of the arrival and service rates and state probabilities.

5. Express all the state probabilities in terms of the empty state probability, using the inter-state transition relationships.

6. Determine the empty state probability by using the fact that all state probabilities always sum to 1. Whereas specific problems that have small finite state models are often able to be analysed numerically, analysis of more general models, using calculus, yields useful formulae that can be applied to whole classes of problems.

2.3 SINGLE-SERVER QUEUE

Single-server queues are, perhaps, the most commonly encountered queueing situation in real life. One encounters a queue with a single server in many situations, including business (e.g. sales clerk), industry (e.g. a production line), transport (e.g. a bus, a taxi rank, an intersection), telecommunications (e.g. Telephone line), computing (e.g. processor sharing). Even where there are multiple servers handling the situation it is possible to consider each server individually as part of the larger system, in many cases. (e.g A supermarket checkout has several single server queues that the customer can select from.) Consequently, being able to model and analyse a single server queue's behaviour is a particularly useful thing to do. Poisson arrivals and service M/M/1/∞/∞ represents a single server that has unlimited queue capacity and infinite calling population, both arrivals and service are Poisson (or random) processes, meaning the statistical distribution of both the inter-arrival times and the service times follow the exponential distribution. Because of the mathematical nature of the exponential distribution, a number of quite simple relationships are able to be derived for several performance measures based on knowing the arrival rate and service rate. This is fortunate because, an M/M/1 queuing model can be used to approximate many queuing situations.

Poisson arrivals and general service M/G/1/∞/∞ represents a single server that has unlimited queue capacity and infinite calling population, while the arrival is still Poisson process, meaning the statistical


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distribution of the inter-arrival times still follow the exponential distribution, the distribution of the service time does not. The distribution of the service time may follow any general statistical distribution, not just exponential. Relationships are still able to be derived for a (limited) number of performance measures if one knows the arrival rate and the mean and variance of the service rate. However the derivations a generally more complex. A number of special cases of M/G/1 provide specific solutions that give broad insights into the best model to choose for specific queueing situations because they permit the comparison of those solutions to the performance of an M/M/1 model.

2.4 MULTIPLE-SERVERS QUEUE Multiple (identical)-servers queue situations are frequently encountered in telecommunications or a customer service environment. When modelling these situations care is needed to ensure that it is a multiple servers queue, not a network of single server queues, because results may differ depending on how the queuing model behaves. One observational insight provided by comparing queuing models is that a single queue with multiple servers performs better than each server having their own queue and that a single large pool of servers performs better than two or more smaller pools, even though there are the same total number of servers in the system. One simple example to prove the above fact is as follows: Consider a system having 8 input lines, single queue and 8 servers.The output line has a capacity of 64 kbit/s. Considering the arrival rate at each input as 2 packets/s. So, the total arrival rate is 16 packets/s. With an average of 2000 bits per packet, the service rate is 64 kbit/s/2000b = 32 packets/s. Hence, the average response time of the system is 1/(μ-λ) = 1/(32-16) = 0.0667 sec. Now, consider a second system with 8 queues, one for each server. Each of the 8 output lines has a capacity of 8 kbit/s. The calculation yields the response time as 1/(μ-λ) = 1/(4-2) = 0.5 sec. And the average waiting time in the queue in the first case is ρ/(1-ρ)μ = 0.25, while in the second case is 0.03125. Infinitely many servers While never exactly encountered in reality, an infinite-servers (e.g. M/M/∞) model is a convenient theoretical model for situations that involve storage or delay, such as parking lots, warehouses and even atomic transitions. In these models there is no queue, as such, instead each arriving customer receives service. When viewed from the outside, the model appears to delay or store each customer for some time.

2.5 QUEUEING SYSTEM CLASSIFICATION

With Little's Theorem, we have developed some basic understanding of a queueing system. To further our understanding we will have to dig deeper into characteristics of a queueing system that impact its performance. For example, queueing requirements of a restaurant will depend upon factors like:

How do customers arrive in the restaurant? Are customer arrivals more during lunch and dinner time (a regular restaurant)? Or is the customer traffic more uniformly distributed (a cafe)?


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How much time do customers spend in the restaurant? Do customers typically leave the restaurant in a fixed amount of time? Does the customer service time vary with the type of customer?

How many tables does the restaurant have for servicing customers? The above three points correspond to the most important characteristics of a queueing system. They are explained below:

Arrival Process The probability density distribution that determines the customer arrivals in the system.

In a messaging system, this refers to the message arrival probability distribution.

Service Process The probability density distribution that determines the customer service times in the system.

In a messaging system, this refers to the message transmission time distribution. Since message transmission is directly proportional to the length of the message, this parameter indirectly refers to the message length distribution.

Number of Servers

Number of servers available to service the customers. In a messaging system, this refers to the number of

links between the source and destination nodes.

Based on the above characteristics, queueing systems can be classified by the following convention: A/S/n Where A is the arrival process, S is the service process and n is the number of servers. A and S are can be any of the following: M (Markov) Exponential probability density D (Deterministic) All customers have the same value G (General) Any arbitrary probability distribution Examples of queueing systems that can be defined with this convention are:

M/M/1: This is the simplest queueing system to analyze. Here the arrival and service time are negative exponentially distributed (poisson process). The system consists of only one server. This queueing system can be applied to a wide variety of problems as any system with a very large number of independent customers can be approximated as a Poisson process. Using a Poisson process for service time however is not applicable in many applications and is only a crude approximation. Refer to M/M/1 Queuing System for details.

M/D/n: Here the arrival process is poisson and the service time distribution is deterministic. The system has n servers. (e.g. a ticket booking counter with n cashiers.) Here the service time can be assumed to be same for all customers)

G/G/n: This is the most general queueing system where the arrival and service time processes are both arbitrary. The system has n servers. No analytical solution is known for this queueing system. Markovian arrival processes


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In queuing theory, Markovian arrival processes are used to model the arrival customers to queue. Some of the most common include the Poisson process, Markovian arrival process and the batch Markovian arrival process. Markovian arrival processes has two processes. A continuous-time Markov process j(t), a Markov process which is generated by a generator or rate matrix, Q. The other process is a counting process N(t), which has state space (where is the set of all natural numbers). N(t) increases every time there is a transition in j(t) which marked.

2.6 POISSON PROCESS

The Poisson arrival process or Poisson process counts the number of arrivals, each of which has a exponentially distributed time between arrival. In the most general case this can be represented by the rate matrix, Markov arrival process The Markov arrival process (MAP) is a generalisation of the Poisson process by having non-exponential distribution sojourn between arrivals. The homogeneous case has rate matrix, Little's law In queueing theory, Little's result, theorem, lemma, or law says: The average number of customers in a stable system (over some time interval), N, is equal to their average arrival rate, λ, multiplied by their average time in the system, T, or:

Although it looks intuitively reasonable, it's a quite remarkable result, as it implies that this behavior is entirely independent of any of the detailed probability distributions involved, and hence requires no assumptions about the schedule according to which customers arrive or are serviced, or whether they are served in the order in which they arrive. It is also a comparatively recent result - it was first proved by John Little, an Institute Professor and the Chair of Management Science at the MIT Sloan School of Management, in 1961. Handily his result applies to any system, and particularly, it applies to systems within systems. So in a bank, the queue might be one subsystem, and each of the tellers another subsystem, and Little's result could be applied to each one, as well as the whole thing. The only requirement is that the system is stable -- it can't be in some transition state such as just starting up or just shutting down.

2.6.1 Mathematical formalization of Little's theorem

Let α(t) be to some system in the interval [0, t]. Let β(t) be the number of departures from the same system in the interval [0, t]. Both α(t) and β(t) are integer valued increasing functions by their definition. Let Tt be the mean time spent in the system (during the interval [0, t]) for all the customers who were in the system during the interval [0, t]. Let Nt be the mean number of customers in the system over the duration of the interval [0, t].


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If the following limits exist,

and, further, if λ = δ then Little's theorem holds, the limit

exists and is given by Little's theorem,

Ideal Performance


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2.8 EFFECTS OF CONGESTION

‘ 2.9 CONGESTION-CONTROL MECHANISMS Backpressure Request from destination to source to reduce rate Useful only on a logical connection basis Requires hop-by-hop flow control mechanism Policing Measuring and restricting packets as they enter the network Choke packet Specific message back to source E.g., ICMP Source Quench Implicit congestion signaling

2.9.1 Explicit congestion signaling

Frame Relay reduces network overhead by implementing simple congestion-notification mechanisms rather than explicit, per-virtual-circuit flow control. Frame Relay typically is implemented on reliable network media, so data


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integrity is not sacrificed because flow control can be left to higher-layer protocols. Frame Relay implements two congestion-notification mechanisms: • Forward-explicit congestion notification (FECN) • Backward-explicit congestion notification (BECN) FECN and BECN each is controlled by a single bit contained in the Frame Relay frame header. The Frame Relay frame header also contains a Discard Eligibility (DE) bit, which is used to identify less important traffic that can be dropped during periods of congestion. The FECN bit is part of the Address field in the Frame Relay frame header. The FECN mechanism is initiated when a DTE device sends Frame Relay frames into the network. If the network is congested, DCE devices (switches) set the value of the frames' FECN bit to 1. When the frames reach the destination DTE device, the Address field (with the FECN bit set) indicates that the frame experienced congestion in the path from source to destination. The DTE device can relay this information to a higher-layer protocol for processing. Depending on the implementation, flow control may be initiated, or the indication may be ignored. The BECN bit is part of the Address field in the Frame Relay frame header. DCE devices set the value of the BECN bit to 1 in frames traveling in the opposite direction of frames with their FECN bit set. This informs the receiving DTE device that a particular path through the network is congested. The DTE device then can relay this information to a higher-layer protocol for processing. Depending on the implementation, flow-control may be initiated, or the indication may be ignored. Frame Relay Discard Eligibility

The Discard Eligibility (DE) bit is used to indicate that a frame has lower importance than other frames. The DE bit is part of the Address field in the Frame Relay frame header. DTE devices can set the value of the DE bit of a frame to 1 to indicate that the frame has lower importance than other frames. When the network becomes congested, DCE devices will discard frames with the DE bit set before discarding those that do not. This reduces the likelihood of critical data being dropped by Frame Relay DCE devices during periods of congestion. Frame Relay Error Checking Frame Relay uses a common error-checking mechanism known as the cyclic redundancy check (CRC). The CRC compares two calculated values to determine whether errors occurred during the transmission from source to destination. Frame Relay reduces network overhead by implementing error checking rather than error correction. Frame Relay typically is implemented on reliable network media, so data integrity is not sacrificed because error correction can be left to higher-layer protocols running on top of Frame Relay.

2.10 TRAFFIC MANAGEMENT IN CONGESTED NETWORK – SOME CONSIDERATIONS

Fairness


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Various flows should “suffer” equally. Last-in-first-discarded may not be fair Quality of Service (QoS) Flows treated differently, based on need Voice, video: delay sensitive, loss insensitive File transfer, mail: delay insensitive, loss sensitive Interactive computing: delay and loss sensitive Reservations Policing: excess traffic discarded or handled on best-effort basis

2.11 FRAME RELAY CONGESTION CONTROL

Minimize frame discard Maintain QoS (per-connection bandwidth) Minimize monopolization of network Simple to implement, little overhead Minimal additional network traffic Resources distributed fairly Limit spread of congestion Operate effectively regardless of flow Have minimum impact other systems in network Minimize variance in QoS

Congestion Avoidance with Explicit Signaling Two general strategies considered:

Hypothesis 1: Congestion always occurs slowly, almost always at egress nodes forward explicit congestion avoidance Hypothesis 2: Congestion grows very quickly in internal nodes and requires quick

action backward explicit congestion avoidance

Explicit Signaling Response

Network Response each frame handler monitors its queuing behavior and takes action


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use FECN/BECN bits some/all connections notified of congestion User (end-system) Response receipt of BECN/FECN bits in frame BECN at sender: reduce transmission rate FECN at receiver: notify peer (via LAPF or higher layer) to restrict flow

Frame Relay Traffic Rate Management Parameters

Committed Information Rate (CIR) Average data rate in bits/second that the network agrees to support for a

connection Data Rate of User Access Channel (Access Rate) Fixed rate link between user and network (for network access) Committed Burst Size (Bc) Maximum data over an interval agreed to by network Excess Burst Size (Be) Maximum data, above Bc, over an interval that network will attempt to

transfer

Relationship of Congestion Parameters


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UNIT- 03 TCP AND CONGESTION CONTROL

3.1 TCP FLOW CONTROL Uses a form of sliding window. Differs from mechanism used in LLC, HDLC, X.25, and others:

Decouples acknowledgement of received data units from granting permission to send more.

TCP’s flow control is known as a credit allocation scheme: Each transmitted octet is considered to have a sequence number.

TCP Header Fields for Flow Control: Sequence number (SN) of first octet in data segment. Acknowledgement number (AN). Window (W) Acknowledgement contains AN = i, W = j:

Octets through SN = i - 1 acknowledged. Permission is granted to send W = j more octets,

i.e., octets i through i + j - 1

TCP Credit Allocation Mechanisms


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Credit Allocation Is Fexible: Suppose last message B issued was AN = i, W = j. To increase credit to k (k > j) when no new data, B issues AN = i, W = k. To acknowledge segment containing m octets (m < j), B issues AN = i + m, W = j - m.

Credit Policy: Receiver needs a policy for how much credit to give sender Conservative approach: grant credit up to limit of available buffer space May limit throughput in long-delay situations Optimistic approach: grant credit based on expectation of freeing space before data

arrives.

Effect Of Window Size: W = TCP window size (octets) R = Data rate (bps) at TCP source D = Propagation delay (seconds)

After TCP source begins transmitting, it takes D seconds for first octet to arrive, and D seconds for acknowledgement to return.

TCP source could transmit at most 2RD bits, or RD/4 octets.

Sending and receiving Flow Control Perceptives


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Normalized Throughput: 1 W > RD / 4 S = 4W W < RD / 4 RD

Complication Factor: Multiple TCP connections are multiplexed over same network interface, reducing R

and efficiency For multi-hop connections, D is the sum of delays across each network plus delays at

each router If source data rate R exceeds data rate on one of the hops, that hop will be a bottleneck Lost segments are retransmitted, reducing throughput. Impact depends on

retransmission policy.

Rewtransmission Fails: TCP relies exclusively on positive acknowledgements and retransmission on

acknowledgement timeout There is no explicit negative acknowledgement Retransmission required when:

1. Segment arrives damaged, as indicated by checksum error, causing receiver to discard segment

2. Segment fails to arrive.

Timers: A timer is associated with each segment as it is sent If timer expires before segment acknowledged, sender must retransmit Key Design Issue: value of retransmission timer Too small: many unnecessary retransmissions, wasting network bandwidth Too large: delay in handling lost segment.

Implementation Policy: Send Deliver Accept


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In-order In-window

Retransmit First-only Batch individual

Acknowledge immediate cumulative.

3.2 TCP CONGESTION CONTROL Dynamic routing can alleviate congestion by spreading load more evenly But only effective for unbalanced loads and brief surges in traffic Congestion can only be controlled by limiting total amount of data entering network ICMP source Quench message is crude and not effective RSVP may help but not widely implemented TCP Congestion Control is Difficult IP is connectionless and stateless, with no provision for detecting or controlling congestion TCP only provides end-to-end flow control No cooperative, distributed algorithm to bind together various TCP entities TCP Flow and Congestion Control The rate at which a TCP entity can transmit is determined by rate of incoming ACKs to

previous segments with new credit Rate of Ack arrival determined by round-trip path between source and destination Bottleneck may be destination or internet Sender cannot tell which Only the internet bottleneck can be due to congestion TCP Segment Pacing


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3.2.1 TCP FLOW AND CONGESTION CONTROL

3.3 RETRANSMISSION TIMER MANAGEMENT Three Techniques to calculate retransmission timer (RTO): RTT Variance Estimation Exponential RTO Backoff Karn’s Algorithm

RTTVarianceEstimation (Jacobson’s Algorithm) 3 sources of high variance in RTT If data rate relative low, then transmission delay will be relatively large, with larger

variance due to variance in packet size Load may change abruptly due to other sources Peer may not acknowledge segments immediately

Jacobson’s Algorithm SRTT(K + 1) = (1 – g) × SRTT(K) + g × RTT(K + 1) SERR(K + 1) = RTT(K + 1) – SRTT(K) SDEV(K + 1) = (1 – h) × SDEV(K) + h ×|SERR(K + 1)| RTO(K + 1) = SRTT(K + 1) + f × SDEV(K + 1) g = 0.125 h = 0.25 f = 2 or f = 4 (most current implementations use f = 4) Two Other Factors Jacobson’s algorithm can significantly improve TCP performance, but: What RTO to use for retransmitted segments?


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ANSWER: exponential RTO backoff algorithm Which round-trip samples to use as input to Jacobson’s algorithm?

ANSWER: Karn’s algorithm 3.4 EXPONENTIAL RTO BACKOFF Increase RTO each time the same segment retransmitted – backoff process Multiply RTO by constant:

RTO = q × RTO q = 2 is called binary exponential backoff

Which Round-trip Samples? If an ack is received for retransmitted segment, there are 2 possibilities:

Ack is for first transmission Ack is for second transmission TCP source cannot distinguish 2 cases No valid way to calculate RTT:

From first transmission to ack, or From second transmission to ack?

3.5 KARN’S ALGORITHM Do not use measured RTT to update SRTT and SDEV Calculate backoff RTO when a retransmission occurs Use backoff RTO for segments until an ack arrives for a segment that has not been

retransmitted Then use Jacobson’s algorithm to calculate RTO

3.6 WINDOW MANAGEMENT Slow start Dynamic window sizing on congestion Fast retransmit Fast recovery Limited transmit

Slow Start awnd = MIN[ credit, cwnd] where awnd = allowed window in segments cwnd = congestion window in segments credit = amount of unused credit granted in most recent ack cwnd = 1 for a new connection and increased by 1 for each ack received, up to a maximum


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Effect of Slow Start

Dynamic Window Sizing on Congestion A lost segment indicates congestion Prudent to reset cwsd = 1 and begin slow start process May not be conservative enough: “ easy to drive a network into saturation but hard for

the net to recover” (Jacobson) Instead, use slow start with linear growth in cwnd

Illustration of Slow Start and Congestion Avoidance


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Fast Retransmit RTO is generally noticeably longer than actual RTT If a segment is lost, TCP may be slow to retransmit TCP rule: if a segment is received out of order, an ack must be issued immediately for the

last in-order segment Fast Retransmit rule: if 4 acks received for same segment, highly likely it was lost, so

retransmit immediately, rather than waiting for timeout

Fast Recovery When TCP retransmits a segment using Fast Retransmit, a segment was assumed lost Congestion avoidance measures are appropriate at this point E.g., slow-start/congestion avoidance procedure This may be unnecessarily conservative since multiple acks indicate segments are getting

through Fast Recovery: retransmit lost segment, cut cwnd in half, proceed with linear increase of

cwnd This avoids initial exponential slow-start Limited Transmit If congestion window at sender is small, fast retransmit may not get triggered, e.g., cwnd =

3 Under what circumstances does sender have small congestion window? Is the problem common? If the problem is common, why not reduce number of duplicate acks needed to trigger

retransmit? Limited Transmit Algorithm Sender can transmit new segment when 3 conditions are met: Two consecutive duplicate acks are received


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Destination advertised window allows transmission of segment Amount of outstanding data after sending is less than or equal to cwnd + 2

3.7 PERFORMANCE OF TCP OVER ATM How best to manage TCP’s segment size, window management and congestion

control… …at the same time as ATM’s quality of service and traffic control policies TCP may operate end-to-end over one ATM network, or there may be multiple ATM

LANs or WANs with non-ATM networks TCP/IP over AAL5/ATM

Performance of TCP over UBR Buffer capacity at ATM switches is a critical parameter in assessing TCP throughput

performance Insufficient buffer capacity results in lost TCP segments and retransmissions

Effect of Switch Buffer Size Data rate of 141 Mbps End-to-end propagation delay of 6 μs IP packet sizes of 512 octets to 9180 TCP window sizes from 8 Kbytes to 64 Kbytes ATM switch buffer size per port from 256 cells to 8000 One-to-one mapping of TCP connections to ATM virtual circuits TCP sources have infinite supply of data ready Observations If a single cell is dropped, other cells in the same IP datagram are unusable, yet ATM

network forwards these useless cells to destination Smaller buffer increase probability of dropped cells


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Larger segment size increases number of useless cells transmitted if a single cell dropped

Partial Packet and Early Packet Discard Reduce the transmission of useless cells Work on a per-virtual circuit basis Partial Packet Discard

If a cell is dropped, then drop all subsequent cells in that segment (i.e., look for cell with SDU type bit set to one)

Early Packet Discard When a switch buffer reaches a threshold level, preemptively discard all cells in

a segment Selective Drop Ideally, N/V cells buffered for each of the V virtual circuits W(i) = N(i) = N(i) × V

N/V N If N > R and W(i) > Z

then drop next new packet on VC i Z is a parameter to be chosen

ATM Switch Buffer Layout

Fair Buffer Allocation More aggressive dropping of packets as congestion increases Drop new packet when:

N > R and W(i) > Z × B – R N - R TCP over ABR Good performance of TCP over UBR can be achieved with minor adjustments to switch

mechanisms This reduces the incentive to use the more complex and more expensive ABR service Performance and fairness of ABR quite sensitive to some ABR parameter settings


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Overall, ABR does not provide significant performance over simpler and less expensive UBR-EPD or UBR-EPD-FBA

3.8 TRAFFIC AND CONGESTION CONTROL IN ATM NETWORKS Introduction Control needed to prevent switch buffer overflow High speed and small cell size gives different problems from other networks Limited number of overhead bits ITU-T specified restricted initial set

– I.371 ATM forum Traffic Management Specification 41

Overview Congestion problem Framework adopted by ITU-T and ATM forum

Control schemes for delay sensitive traffic Voice & video

Not suited to bursty traffic Traffic control Congestion control

Bursty traffic Available Bit Rate (ABR) Guaranteed Frame Rate (GFR)

3.9 REQUIREMENTS FOR ATM TRAFFIC AND CONGESTION CONTROL Most packet switched and frame relay networks carry non-real-time bursty data

No need to replicate timing at exit node Simple statistical multiplexing User Network Interface capacity slightly greater than average of channels

Congestion control tools from these technologies do not work in ATM

Problems with ATM Congestion Control Most traffic not amenable to flow control

Voice & video can not stop generating Feedback slow

Small cell transmission time v propagation delay Wide range of applications

From few kbps to hundreds of Mbps Different traffic patterns Different network services

High speed switching and transmission Volatile congestion and traffic control

Key Performance Issues-Latency/Speed Effects E.g. data rate 150Mbps Takes (53 x 8 bits)/(150 x 106) =2.8 x 10-6 seconds to insert a cell


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Transfer time depends on number of intermediate switches, switching time and propagation delay. Assuming no switching delay and speed of light propagation, round trip delay of 48 x 10-3 sec across USA

A dropped cell notified by return message will arrive after source has transmitted N further cells

N=(48 x 10-3 seconds)/(2.8 x 10-6 seconds per cell) =1.7 x 104 cells = 7.2 x 106 bits i.e. over 7 Mbits

Cell Delay Variation For digitized voice delay across network must be small Rate of delivery must be constant Variations will occur Dealt with by Time Reassembly of CBR cells (see next slide) Results in cells delivered at CBR with occasional gaps due to dropped cells Subscriber requests minimum cell delay variation from network provider

Increase data rate at UNI relative to load Increase resources within network

Time Reassembly of CBR Cells

Network Contribution to Cell Delay Variation In packet switched network

Queuing effects at each intermediate switch Processing time for header and routing

Less for ATM networks Minimal processing overhead at switches

Fixed cell size, header format No flow control or error control processing

ATM switches have extremely high throughput Congestion can cause cell delay variation

Build up of queuing effects at switches


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Total load accepted by network must be controlled Cell Delay Variation at UNI Caused by processing in three layers of ATM model

– See next slide for details None of these delays can be predicted None follow repetitive pattern So, random element exists in time interval between reception by ATM stack and

transmission

3.10 ATM TRAFFIC-RELATED ATTRIBUTES Six service categories (see chapter 5)

Constant bit rate (CBR) Real time variable bit rate (rt-VBR) Non-real-time variable bit rate (nrt-VBR) Unspecified bit rate (UBR) Available bit rate (ABR) Guaranteed frame rate (GFR)

Characterized by ATM attributes in four categories Traffic descriptors QoS parameters Congestion Other

Traffic Parameters Traffic pattern of flow of cells

Intrinsic nature of traffic Source traffic descriptor

Modified inside network Connection traffic descriptor

Source Traffic Descriptor Peak cell rate

Upper bound on traffic that can be submitted Defined in terms of minimum spacing between cells T PCR = 1/T Mandatory for CBR and VBR services

Sustainable cell rate Upper bound on average rate Calculated over large time scale relative to T Required for VBR Enables efficient allocation of network resources between VBR sources Only useful if SCR < PCR

Maximum burst size Max number of cells that can be sent at PCR If bursts are at MBS, idle gaps must be enough to keep overall rate below SCR Required for VBR


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Minimum cell rate Min commitment requested of network Can be zero Used with ABR and GFR ABR & GFR provide rapid access to spare network capacity up to PCR PCR – MCR represents elastic component of data flow Shared among ABR and GFR flows

Maximum frame size Max number of cells in frame that can be carried over GFR connection Only relevant in GFR

Connection Traffic Descriptor

Includes source traffic descriptor plus:- Cell delay variation tolerance

Amount of variation in cell delay introduced by network interface and UNI Bound on delay variability due to slotted nature of ATM, physical layer

overhead and layer functions (e.g. cell multiplexing) Represented by time variable τ

Conformance definition Specify conforming cells of connection at UNI Enforced by dropping or marking cells over definition

Quality of Service Parameters-maxCTD

Cell transfer delay (CTD) Time between transmission of first bit of cell at source and reception of last

bit at destination Typically has probability density function (see next slide) Fixed delay due to propagation etc. Cell delay variation due to buffering and scheduling Maximum cell transfer delay (maxCTD)is max requested delay for

connection Fraction α of cells exceed threshold Discarded or delivered late

Peak-to-peak CDV & CLR

Peak-to-peak Cell Delay Variation Remaining (1-α) cells within QoS Delay experienced by these cells is between fixed delay and maxCTD This is peak-to-peak CDV CDVT is an upper bound on CDV

Cell loss ratio Ratio of cells lost to cells transmitted

Cell Transfer Delay PDF


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Congestion Control Attributes

Only feedback is defined ABR and GFR Actions taken by network and end systems to regulate traffic submitted

ABR flow control Adaptively share available bandwidth

Other Attributes Behaviour class selector (BCS)

Support for IP differentiated services (chapter 16) Provides different service levels among UBR connections Associate each connection with a behaviour class May include queuing and scheduling

Minimum desired cell rate 3.11 TRAFFIC MANAGEMENT FRAMEWORK Objectives of ATM layer traffic and congestion control

Support QoS for all foreseeable services Not rely on network specific AAL protocols nor higher layer application

specific protocols Minimize network and end system complexity Maximize network utilization

Timing Levels Cell insertion time Round trip propagation time Connection duration Long term

Traffic Control and Congestion Functions


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Traffic Control Strategy Determine whether new ATM connection can be accommodated Agree performance parameters with subscriber Traffic contract between subscriber and network This is congestion avoidance If it fails congestion may occur

– Invoke congestion control

3.12 TRAFFIC CONTROL Resource management using virtual paths Connection admission control Usage parameter control Selective cell discard Traffic shaping Explicit forward congestion indication

Resource Management Using Virtual Paths Allocate resources so that traffic is separated according to service characteristics Virtual path connection (VPC) are groupings of virtual channel connections (VCC)

Applications User-to-user applications

VPC between UNI pair No knowledge of QoS for individual VCC User checks that VPC can take VCCs’ demands

User-to-network applications VPC between UNI and network node Network aware of and accommodates QoS of VCCs

Network-to-network applications VPC between two network nodes


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Network aware of and accommodates QoS of VCCs

Resource Management Concerns Cell loss ratio Max cell transfer delay Peak to peak cell delay variation All affected by resources devoted to VPC If VCC goes through multiple VPCs, performance depends on consecutive VPCs and

on node performance – VPC performance depends on capacity of VPC and traffic characteristics of

VCCs – VCC related function depends on switching/processing speed and priority

VCCs and VPCs Configuration

Allocation of Capacity to VPC Aggregate peak demand

May set VPC capacity (data rate) to total of VCC peak rates Each VCC can give QoS to accommodate peak demand VPC capacity may not be fully used

Statistical multiplexing VPC capacity >= average data rate of VCCs but < aggregate peak demand Greater CDV and CTD May have greater CLR More efficient use of capacity For VCCs requiring lower QoS Group VCCs of similar traffic together

Connection Admission Control User must specify service required in both directions

Category Connection traffic descriptor

Source traffic descriptor


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CDVT Requested conformance definition

QoS parameter requested and acceptable value Network accepts connection only if it can commit resources to support requests

Cell Loss Priority Two levels requested by user

Priority for individual cell indicated by CLP bit in header If two levels are used, traffic parameters for both flows specified

High priority CLP = 0 All traffic CLP = 0 + 1

May improve network resource allocation Procedures to Set Traffic Control Parameters

Usage Parameter Control UPC Monitors connection for conformity to traffic contract Protect network resources from overload on one connection Done at VPC or VCC level VPC level more important

– Network resources allocated at this level Location of UPC Function


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Peak Cell Rate Algorithm How UPC determines whether user is complying with contract Control of peak cell rate and CDVT

– Complies if peak does not exceed agreed peak – Subject to CDV within agreed bounds – Generic cell rate algorithm – Leaky bucket algorithm

Generic Cell Rate Algorithm

Virtual Scheduling Algorithm

Leaky Bucket Algorithm


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Continuous Leaky Bucket Algorithm

Sustainable Cell Rate Algorithm Operational definition of relationship between sustainable cell rate and burst tolerance Used by UPC to monitor compliance Same algorithm as peak cell rate

UPC Actions Compliant cell pass, non-compliant cells discarded If no additional resources allocated to CLP=1 traffic, CLP=0 cells C If two level cell loss priority cell with:

– CLP=0 and conforms passes – CLP=0 non-compliant for CLP=0 traffic but compliant for CLP=0+1 is tagged

and passes – CLP=0 non-compliant for CLP=0 and CLP=0+1 traffic discarded – CLP=1 compliant for CLP=0+1 passes – CLP=1 non-compliant for CLP=0+1 discarded

Possible Actions of UPC


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Explicit Forward Congestion Indication Essentially same as frame relay If node experiencing congestion, set forward congestion indication is cell headers

– Tells users that congestion avoidance should be initiated in this direction – User may take action at higher level

3.13 ABR TRAFFIC MANAGEMENT QoS for CBR, VBR based on traffic contract and UPC described previously No congestion feedback to source Open-loop control Not suited to non-real-time applications

File transfer, web access, RPC, distributed file systems No well defined traffic characteristics except PCR PCR not enough to allocate resources

Use best efforts or closed-loop control Best Efforts Share unused capacity between applications As congestion goes up:

Cells are lost Sources back off and reduce rate Fits well with TCP techniques (chapter 12) Inefficient

Cells dropped causing re-transmission Closed-Loop Control Sources share capacity not used by CBR and VBR Provide feedback to sources to adjust load Avoid cell loss Share capacity fairly


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Characteristics of ABR ABR connections share available capacity

Access instantaneous capacity unused by CBR/VBR Increases utilization without affecting CBR/VBR QoS

Share used by single ABR connection is dynamic Varies between agreed MCR and PCR

Network gives feedback to ABR sources ABR flow limited to available capacity Buffers absorb excess traffic prior to arrival of feedback

Low cell loss Major distinction from UBR

Feedback Mechanisms Cell transmission rate characterized by:

Allowable cell rate Current rate

Minimum cell rate Min for ACR May be zero

Peak cell rate Max for ACR

Initial cell rate Start with ACR=ICR Adjust ACR based on feedback Feedback in resource management (RM) cells

Cell contains three fields for feedback Congestion indicator bit (CI) No increase bit (NI) Explicit cell rate field (ER)

Source Reaction to Feedback If CI=1

Reduce ACR by amount proportional to current ACR but not less than CR Else if NI=0

Increase ACR by amount proportional to PCR but not more than PCR If ACR>ER set ACR<-max[ER,MCR]

Cell Flow on ABR Two types of cell Data & resource management (RM) Source receives regular RM cells

Feedback Bulk of RM cells initiated by source

One forward RM cell (FRM) per (Nrm-1) data cells


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Nrm preset – usually 32 Each FRM is returned by destination as backwards RM (BRM) cell FRM typically CI=0, NI=0 or 1 ER desired transmission rate in range

ICR<=ER<=PCR Any field may be changed by switch or destination before return

ATM Switch Rate Control Feedback EFCI marking

Explicit forward congestion indication Causes destination to set CI bit in ERM

Relative rate marking Switch directly sets CI or NI bit of RM If set in FRM, remains set in BRM Faster response by setting bit in passing BRM Fastest by generating new BRM with bit set

Explicit rate marking Switch reduces value of ER in FRM or BRM

Flow of Data and RM Cells

ARB Feedback v TCP ACK ABR feedback controls rate of transmission

Rate control TCP feedback controls window size

Credit control ARB feedback from switches or destination TCP feedback from destination only


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3.14 RM CELL FORMAT

RM Cell Format Notes ATM header has PT=110 to indicate RM cell On virtual channel VPI and VCI same as data cells on connection On virtual path VPI same, VCI=6 Protocol id identifies service using RM (ARB=1) Message type

Direction FRM=0, BRM=1 BECN cell. Source (BN=0) or switch/destination (BN=1) CI (=1 for congestion) NI (=1 for no increase) Request/Acknowledge (not used in ATM forum spec)

3.15 ABR CAPACITY ALLOCATION ATM switch must perform:

Congestion control Monitor queue length Fair capacity allocation Throttle back connections using more than fair share

ATM rate control signals are explicit TCP are implicit

Increasing delay and cell loss

Congestion Control Algorithms-Binary Feedback Use only EFCI, CI and NI bits Switch monitors buffer utilization When congestion approaches, binary notification


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Set EFCI on forward data cells or CI or NI on FRM or BRM Three approaches to which to notify

Single FIFO queue Multiple queues Fair share notification

Single FIFO Queue When buffer use exceeds threshold (e.g. 80%)

Switch starts issuing binary notifications Continues until buffer use falls below threshold Can have two thresholds

One for start and one for stop Stops continuous on/off switching

Biased against connections passing through more switches Multiple Queues Separate queue for each VC or group of VCs Separate threshold on each queue Only connections with long queues get binary notifications

– Fair – Badly behaved source does not affect other VCs – Delay and loss behaviour of individual VCs separated

Can have different QoS on different VCs Fair Share Selective feedback or intelligent marking Try to allocate capacity dynamically E.g. fairshare =(target rate)/(number of connections) Mark any cells where CCR>fairshare

Explicit Rate Feedback Schemes Compute fair share of capacity for each VC Determine current load or congestion Compute explicit rate (ER) for each connection and send to source Three algorithms

Enhanced proportional rate control algorithm EPRCA

Explicit rate indication for congestion avoidance ERICA

Congestion avoidance using proportional control CAPC

Enhanced Proportional Rate Control Algorithm(EPRCA) Switch tracks average value of current load on each connection

Mean allowed cell rate (MARC) MACR(I)=(1-α)*(MACR(I-1) + α*CCR(I) CCR(I) is CCR field in Ith FRM


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Typically α=1/16 Bias to past values of CCR over current Gives estimated average load passing through switch If congestion, switch reduces each VC to no more than DPF*MACR

DPF=down pressure factor, typically 7/8 ER<-min[ER, DPF*MACR]

Load Factor Adjustments based on load factor LF=Input rate/target rate

Input rate measured over fixed averaging interval Target rate slightly below link bandwidth (85 to 90%) LF>1 congestion threatened

VCs will have to reduce rate

Explicit Rate Indication for Congestion Avoidance (ERICA)

Attempt to keep LF close to 1 Define:

fairshare = (target rate)/(number of connections) VCshare = CCR/LF = (CCR/(Input Rate)) *(Target Rate)

ERICA selectively adjusts VC rates – Total ER allocated to connections matches target rate – Allocation is fair – ER = max[fairshare, VCshare] – VCs whose VCshare is less than their fairshare get greater increase

Congestion Avoidance Using Proportional Control (CAPC)

If LF<1 fairshare<-fairshare*min[ERU,1+(1-LF)*Rup] If LF>1 fairshare<-fairshare*min[ERU,1-(1-LF)*Rdn] ERU>1, determines max increase Rup between 0.025 and 0.1, slope parameter Rdn, between 0.2 and 0.8, slope parameter ERF typically 0.5, max decrease in allottment of fair share If fairshare < ER value in RM cells, ER<-fairshare Simpler than ERICA Can show large rate oscillations if RIF (Rate increase factor) too high Can lead to unfairness

GRF Overview

Simple as UBR from end system view

End system does no policing or traffic shaping May transmit at line rate of ATM adaptor

Modest requirements on ATM network No guarantee of frame delivery Higher layer (e.g. TCP) react to congestion causing dropped frames


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User can reserve cell rate capacity for each VC Application can send at min rate without loss

Network must recognise frames as well as cells If congested, network discards entire frame All cells of a frame have same CLP setting

CLP=0 guaranteed delivery, CLP=1 best efforts

GFR Traffic Contract

Peak cell rate PCR Minimum cell rate MCR Maximum burst size MBS Maximum frame size MFS Cell delay variation tolerance CDVT

Mechanisms for supporting Rate Guarantees

Tagging and policing Buffer management Scheduling

Tagging and Policing

Tagging identifies frames that conform to contract and those that don’t

CLP=1 for those that don’t Set by network element doing conformance check May be network element or source showing less important frames

Get lower QoS in buffer management and scheduling Tagged cells can be discarded at ingress to ATM network or subsequent switch Discarding is a policing function

Buffer Management

Treatment of cells in buffers or when arriving and requiring buffering If congested (high buffer occupancy) tagged cells discarded in preference to untagged Discard tagged cell to make room for untagged cell May buffer per-VC Discards may be based on per queue thresholds

Scheduling Give preferential treatment to untagged cells Separate queues for each VC

Per VC scheduling decisions E.g. FIFO modified to give CLP=0 cells higher priority

Scheduling between queues controls outgoing rate of VCs Individual cells get fair allocation while meeting traffic contract


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3.15.1 COMPONENTS OF GFR MECHANISM

GFR Conformance Definition UPC function

UPC monitors VC for traffic conformance Tag or discard non-conforming cells

Frame conforms if all cells in frame conform Rate of cells within contract

Generic cell rate algorithm PCR and CDVT specified for connection All cells have same CLP Within maximum frame size (MFS)

QoS Eligibility Test Test for contract conformance

– Discard or tag non-conforming cells Looking at upper bound on traffic

– Determine frames eligible for QoS guarantee Under GFR contract for VC Looking at lower bound for traffic

Frames are one of: – Nonconforming: cells tagged or discarded – Conforming ineligible: best efforts – Conforming eligible: guaranteed delivery –

Simplified Frame Based GCRA


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UNIT - 04

INTEGRATED AND DIFFERENTIATED SERVICES INTRODUCTION New additions to Internet increasing traffic High volume client/server application Web Graphics Real time voice and video Need to manage traffic and control congestion IEFT standards Integrated services Collective service to set of traffic demands in domain Limit demand & reserve resources Differentiated services Classify traffic in groups Different group traffic handled differently 4.1 INTEGRATED SERVICES ARCHITECTURE (ISA) IPv4 header fields for precedence and type of service usually ignored ATM only network designed to support TCP, UDP and real-time traffic

May need new installation Need to support Quality of Service (QoS) within TCP/IP

Add functionality to routers Means of requesting QoS

Internet Traffic – Elastic Can adjust to changes in delay and throughput E.g. common TCP and UDP application

E-Mail – insensitive to delay changes FTP – User expect delay proportional to file size

Sensitive to changes in throughput SNMP – delay not a problem, except when caused by congestion Web (HTTP), TELNET – sensitive to delay

Not per packet delay – total elapsed time E.g. web page loading time For small items, delay across internet dominates For large items it is throughput over connection

Need some QoS control to match to demand

Internet Traffic – Inelastic Does not easily adapt to changes in delay and throughput

Real time traffic Throughput

Minimum may be required


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Delay E.g. stock trading

Jitter - Delay variation More jitter requires a bigger buffer E.g. teleconferencing requires reasonable upper bound

Packet loss Inelastic Traffic Problems Difficult to meet requirements on network with variable queuing delays and congestion Need preferential treatment Applications need to state requirements

Ahead of time (preferably) or on the fly Using fields in IP header Resource reservation protocol

Must still support elastic traffic Deny service requests that leave too few resources to handle elastic traffic

demands 4.2 ISA APPROACH Provision of QoS over IP Sharing available capacity when congested Router mechanisms

Routing Algorithms Select to minimize delay

Packet discard Causes TCP sender to back off and reduce load Enahnced by ISA

Flow IP packet can be associated with a flow Distinguishable stream of related IP packets From single user activity Requiring same QoS E.g. one transport connection or one video stream Unidirectional Can be more than one recipient Multicast Membership of flow identified by source and destination IP address, port numbers,

protocol type IPv6 header flow identifier can be used but isnot necessarily equivalent to ISA flow ISA Functions Admission control

For QoS, reservation required for new flow RSVP used

Routing algorithm Base decision on QoS parameters

Queuing discipline


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Take account of different flow requirements Discard policy

Manage congestion Meet QoS

ISA Implementation in Router Background Functions Forwarding functions

4.3 ISA COMPONENTS – BACKGROUND FUNCTIONS Reservation Protocol

RSVP Admission control Management agent

Can use agent to modify traffic control database and direct admission control Routing protocol

ISA Components – Forwarding Classifier and route selection

Incoming packets mapped to classes Single flow or set of flows with same QoS –E.g. all video flows Based on IP header fields

Determines next hop Packet scheduler

Manages one or more queues for each output Order queued packets sent

Based on class, traffic control database, current and past activity on outgoing port


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Policing 4.4 ISA SERVICES Traffic specification (TSpec) defined as service for flow On two levels

General categories of service Guaranteed Controlled load Best effort (default)

Particular flow within category TSpec is part of contract

Token Bucket Many traffic sources can be defined by token bucket scheme Provides concise description of load imposed by flow

Easy to determine resource requirements Provides input parameters to policing function

Token Bucket Diagram

ISA SERVICES Guaranteed Service Assured capacity level or data rate Specific upper bound on queuing delay through network

Must be added to propagation delay or latency to get total delay Set high to accommodate rare long queue delays

No queuing losses I.e. no buffer overflow

E.g. Real time play back of incoming signal can use delay buffer for incoming signal but will not tolerate packet loss


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Controlled Load Tightly approximates to best efforts under unloaded conditions No upper bound on queuing delay High percentage of packets do not experience delay over minimum transit delay Propagation plus router processing with no queuing delay Very high percentage delivered Almost no queuing loss Adaptive real time applications Receiver measures jitter and sets playback point Video can drop a frame or delay output slightly Voice can adjust silence periods

4.5 QUEUING DISCIPLINE Traditionally first in first out (FIFO) or first come first served (FCFS) at each router port No special treatment to high priority packets (flows) Small packets held up by large packets ahead of them in queue

Larger average delay for smaller packets Flows of larger packets get better service

Greedy TCP connection can crowd out altruistic connections If one connection does not back off, others may back off more

4.6 FAIR QUEUING (FQ) Multiple queues for each port

One for each source or flow Queues services round robin Each busy queue (flow) gets exactly one packet per cycle Load balancing among flows No advantage to being greedy

Your queue gets longer, increasing your delay Short packets penalized as each queue sends one packet per cycle

FIFO and FQ

PROCESSOR SHARING Multiple queues as in FQ Send one bit from each queue per round


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Longer packets no longer get an advantage Can work out virtual (number of cycles) start and finish time for a given packet However, we wish to send packets, not bits

BIT-ROUND FAIR QUEUING (BRFQ) Compute virtual start and finish time as before When a packet finished, the next packet sent is the one with the earliest virtual finish

time Good approximation to performance of PS

Throughput and delay converge as time increases Comparison of FIFO, FQ and BRFQ

4.7 GENERALIZED PROCESSOR SHARING (GPS) BRFQ can not provide different capacities to different flows Enhancement called Weighted fair queue (WFQ) From PS, allocate weighting to each flow that determines how many bots are sent during

each round If weighted 5, then 5 bits are sent per round

Gives means of responding to different service requests Guarantees that delays do not exceed bounds 4.8 WEIGHTED FAIR QUEUE Emulates bit by bit GPS Same strategy as BRFQ


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FIFO v WFQ

\ Proactive Packet Discard Congestion management by proactive packet discard

Before buffer full Used on single FIFO queue or multiple queues for elastic traffic E.g. Random Early Detection (RED)

4.9 RANDOM EARLY DETECTION(RED) Surges fill buffers and cause discards On TCP this is a signal to enter slow start phase, reducing load Lost packets need to be resent Adds to load and delay Global synchronization Traffic burst fills queues so packets lost Many TCP connections enter slow start Traffic drops so network under utilized Connections leave slow start at same time causing burst Bigger buffers do not help Try to anticipate onset of congestion and tell one connection to slow down


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RED Design Goals Congestion avoidance Global synchronization avoidance

Current systems inform connections to back off implicitly by dropping packets Avoidance of bias to bursty traffic

Discard arriving packets will do this Bound on average queue length

Hence control on average delay RED Algorithm – Overview Calculate average queue size avg if avg < THmin queue packet else if THmin avg Thmax

calculate probability Pa with probability Pa

discard packet else with probability 1-Pa queue packet else if avg THmax

discard packet RED Buffer

4.10 DIFFERENTIATED SERVICES (DS) ISA and RSVP complex to deploy May not scale well for large volumes of traffic

Amount of control signals Maintenance of state information at routers

DS architecture designed to provide simple, easy to implement, low overhead tool Support range of network services

Differentiated on basis of performance

Characteristics of DS Use IPv4 header Type of Service or IPv6 Traffic Class field No change to IP


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Service level agreement (SLA) established between provider (internet domain) and customer prior to use of DS DS mechanisms not needed in applications Build in aggregation All traffic with same DS field treated same E.g. multiple voice connections DS implemented in individual routers by queuing and forwarding based on DS field State information on flows not saved by routers

Services

Provided within DS domain.Contiguous portion of Internet over which consistent set of DS policies administered.Typically under control of one administrative entity,Defined in SLA.Customer may be user organization or other DS domain.Packet class marked in DS field.Service provider configures forwarding policies routers.Ongoing measure of performance provided for each class.DS domain expected to provide agreed service internally.If destination in another domain, DS domain attempts to forward packets through other domains.Appropriate service level requested from each domain

SLA Parameters Detailed service performance parameters

Throughput, drop probability, latency Constraints on ingress and egress points

Indicate scope of service Traffic profiles to be adhered to

Token bucket Disposition of traffic in excess of profile

Example Services Qualitative

A: Low latency B: Low loss

Quantitative C: 90% in-profile traffic delivered with no more than 50ms latency D: 95% in-profile traffic delivered

Mixed E: Twice bandwidth of F F: Traffic with drop precedence X has higher delivery probability than that with

drop precedence Y DS Field Detail Leftmost 6 bits are DS codepoint

64 different classes available 3 pools

xxxxx0 : reserved for standards –000000 : default packet class –xxx000 : reserved for backwards compatibility with IPv4 TOS xxxx11 : reserved for experimental or local use


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xxxx01 : reserved for experimental or local use but may be allocated for future standards if needed

Rightmost 2 bits unused Configuration Diagram

Configuration – Interior Routers Domain consists of set of contiguous routers Interpretation of DS codepoints within domain is consistent Interior nodes (routers) have simple mechanisms to handle packets based on codepoints

Queuing gives preferential treatment depending on codepoint Per Hop behaviour (PHB) Must be available to all routers Typically the only part implemented in interior routers

Packet dropping rule dictated which to drop when buffer saturated Configuration – Boundary Routers Include PHB rules Also traffic conditioning to provide desired service

Classifier Separate packets into classes

Meter Measure traffic for conformance to profile

Marker Policing by remarking codepoints if required

Shaper Dropper


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DS Traffic Conditioner

PER HOP BEHAVIOUR Expedited forwarding Premium service

Low loss, delay, jitter; assured bandwidth end-to-end service through domains Looks like point to point or leased line Difficult to achieve Configure nodes so traffic aggregate has well defined minimum departure rate

EF PHB Condition aggregate so arrival rate at any node is always less that minimum

departure rate Boundary conditioners Explicit Allocation Superior to best efforts Does not require reservation of resources Does not require detailed discrimination among flows Users offered choice of number of classes Monitored at boundary node In or out depending on matching profile or not Inside network all traffic treated as single pool of packets, distinguished only as in or out Drop out packets before in packets if necessary Different levels of service because different number of in packets for each user PHB - Assured Forwarding Four classes defined

Select one or more to meet requirements Within class, packets marked by customer or provider with one of three drop

precedence values Used to determine importance when dropping packets as result of congestion

Codepoints for AF PHB


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UNIT- 05 PROTOCOLS FOR QOS SUPPORT

INTRODUCTION INCREASED DEMANDS Need to incorporate bursty and stream traffic in TCP/IP architecture Increase capacity

Faster links, switches, routers Intelligent routing policies End-to-end flow control

Multicasting Quality of Service (QoS) capability Transport protocol for streaming Resource Reservation - Unicast Prevention as well as reaction to congestion required Can do this by resource reservation Unicast

End users agree on QoS for task and request from network May reserve resources Routers pre-allocate resources If QoS not available, may wait or try at reduced QoS

Resource Reservation – Multicast Generate vast traffic

High volume application like video Lots of destinations

Can reduce load Some members of group may not want current transmission

“Channels” of video Some members may only be able to handle part of transmission

Basic and enhanced video components of video stream Routers can decide if they can meet demand

Resource Reservation Problems on an Internet Must interact with dynamic routing

Reservations must follow changes in route Soft state – a set of state information at a router that expires unless refreshed

End users periodically renew resource requests 5.1 RESOURCE RESERVATION PROTOCOL (RSVP) DESIGN GOALS Enable receivers to make reservations

Different reservations among members of same multicast group allowed Deal gracefully with changes in group membership

Dynamic reservations, separate for each member of group Aggregate for group should reflect resources needed

Take into account common path to different members of group Receivers can select one of multiple sources (channel selection)


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Deal gracefully with changes in routes Re-establish reservations

Control protocol overheadIndependent of routing protocol RSVP Characteristics Unicast and Multicast Simplex

Unidirectional data flow Separate reservations in two directions

Receiver initiated Receiver knows which subset of source transmissions it wants

Maintain soft state in internet Responsibility of end users

Providing different reservation styles Users specify how reservations for groups are aggregated

Transparent operation through non-RSVP routers Support IPv4 (ToS field) and IPv6 (Flow label field)

5.2 DATA FLOWS - SESSION Data flow identified by destination Resources allocated by router for duration of session Defined by

Destination IP address Unicast or multicast

IP protocol identifier TCP, UDP etc.

Destination port May not be used in multicast

Flow Descriptor Reservation Request

Flow spec Desired QoS Used to set parameters in node’s packet scheduler Service class, Rspec (reserve), Tspec (traffic)

Filter spec Set of packets for this reservation Source address, source prot

5.3 RSVP OPERATION G1, G2, G3 members of multicast group S1, S2 sources transmitting to that group Heavy black line is routing tree for S1, heavy grey line for S2 Arrowed lines are packet transmission from S1 (black) and S2 (grey) All four routers need to know reservation s for each multicast address

– Resource requests must propagate back through routing tree


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Treatment of Packets of One Session at One Router

RSVP Operation Diagram

Filtering G3 has reservation filter spec including S1 and S2 G1, G2 from S1 only R3 delivers from S2 to G3 but does not forward to R4 G1, G2 send RSVP request with filter excluding S2 G1, G2 only members of group reached through R4

R4 doesn’t need to forward packets from this session R4 merges filter spec requests and sends to R3

R3 no longer forwards this session’s packets to R4 Handling of filtered packets not specified


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Here they are dropped but could be best efforts delivery R3 needs to forward to G3

Stores filter spec but doesn’t propagate it Reservation Styles Determines manner in which resource requirements from members of group are

aggregated Reservation attribute

Reservation shared among senders (shared) Characterizing entire flow received on multicast address

Allocated to each sender (distinct) Simultaneously capable of receiving data flow from each sender

Sender selection List of sources (explicit) All sources, no filter spec (wild card)

Reservation Attributes and Styles Reservation Attribute

Distinct Sender selection explicit = Fixed filter (FF) Sender selection wild card = none

Shared Sender selection explicit= Shared-explicit (SE) Sender selection wild card = Wild card filter (WF)

Wild Card Filter Style Single resource reservation shared by all senders to this address If used by all receivers: shared pipe whose capacity is largest of resource requests from

receivers downstream from any point on tree Independent of number of senders using it Propagated upstream to all senders WF(*{Q})

* = wild card sender Q = flowspec

Audio teleconferencing with multiple sites Fixed Filter Style Distinct reservation for each sender Explicit list of senders FF(S1{Q!}, S2{Q2},…) Video distribution.

Shared Explicit Style Single reservation shared among specific list of senders SE(S1, S2, S3, …{Q}) Multicast applications with multiple data sources but unlikely to transmit

simultaneously


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5.4 RSVP Protocol MECHANISMS Two message types

– Resv Originate at multicast group receivers Propagate upstream Merged and packet when appropriate Create soft states Reach sender

– Allow host to set up traffic control for first hop – Path

Provide upstream routing information Issued by sending hosts Transmitted through distribution tree to all destinations

RSVP Host Model

RSVP is a transport layer protocol that enables a network to provide differentiated levels of service to specific flows of data. Ostensibly, different application types have different performance requirements. RSVP acknowledges these differences and provides the mechanisms necessary to detect the levels of performance required by different appli-cations and to modify network behaviors to accommodate those required levels. Over time, as time and latency-sensitive applications mature and proliferate, RSVP's capabilities will become increasingly important. 5.5 Multiprotocol Label Switching (MPLS) Routing algorithms provide support for performance goals

Distributed and dynamic React to congestion Load balance across network

Based on metrics Develop information that can be used in handling different service needs

Enhancements provide direct support IS, DS, RSVP

Nothing directly improves throughput or delay MPLS tries to match ATM QoS support


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Background Efforts to marry IP and ATM IP switching (Ipsilon) Tag switching (Cisco) Aggregate route based IP switching (IBM) Cascade (IP navigator) All use standard routing protocols to define paths between end points Assign packets to path as they enter network Use ATM switches to move packets along paths

ATM switching (was) much faster than IP routers Use faster technology

Developments IETF working group in 1997, proposed standard 2001 Routers developed to be as fast as ATM switches

Remove the need to provide both technologies in same network MPLS does provide new capabilities

QoS support Traffic engineering Virtual private networks Multiprotocol support

Connection Oriented QoS Support Guarantee fixed capacity for specific applications Control latency/jitter Ensure capacity for voice Provide specific, guaranteed quantifiable SLAs Configure varying degrees of QoS for multiple customers MPLS imposes connection oriented framework on IP based internets

Traffic Engineering Ability to dynamically define routes, plan resource commitments based on known

demands and optimize network utilization Basic IP allows primitive traffic engineering

E.g. dynamic routing MPLS makes network resource commitment easy

Able to balance load in face of demand Able to commit to different levels of support to meet user traffic requirements Aware of traffic flows with QoS requirements and predicted demand Intelligent re-routing when congested

VPN Support Traffic from a given enterprise or group passes transparently through an internet Segregated from other traffic on internet Performance guarantees Security


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Multiprotocol Support MPLS can be used on different network technologies IP

– Requires router upgrades Coexist with ordinary routers

ATM – Enables and ordinary switches co-exist

Frame relay – Enables and ordinary switches co-exist

Mixed network 5.6 MPLS OPERATION Label switched routers capable of switching and routing packets based on label

appended to packet Labels define a flow of packets between end points or multicast destinations Each distinct flow (forward equivalence class – FEC) has specific path through LSRs

defined – Connection oriented

Each FEC has QoS requirements IP header not examined

– Forward based on label value MPLS Operation Diagram

Explanation – Setup Labelled switched path established prior to routing and delivery of packets QoS parameters established along path

– Resource commitment – Queuing and discard policy at LSR – Interior routing protocol e.g. OSPF used – Labels assigned


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Local significance only Manually or using Label distribution protocol (LDP) or enhanced

version of RSVP Explanation – Packet Handling Packet enters domain through edge LSR

– Processed to determine QoS LSR assigns packet to FEC and hence LSP

– May need co-operation to set up new LSP Append label Forward packet Within domain LSR receives packet Remove incoming label, attach outgoing label and forward Egress edge strips label, reads IP header and forwards

Notes MPLS domain is contiguous set of MPLS enabled routers Traffic may enter or exit via direct connection to MPLS router or from non-MPLS

router FEC determined by parameters, e.g.

– Source/destination IP address or network IP address – Port numbers – IP protocol id – Differentiated services codepoint – IPv6 flow label

Forwarding is simple lookup in predefined table – Map label to next hop

Can define PHB at an LSR for given FEC Packets between same end points may belong to different FEC

5.7 MPLS PACKET FORWARDING LABEL STACKING Packet may carry number of labels LIFO (stack)

– Processing based on top label – Any LSR may push or pop label

Unlimited levels – Allows aggregation of LSPs into single LSP for part of route – C.f. ATM virtual channels inside virtual paths – E.g. aggregate all enterprise traffic into one LSP for access provider to

handleReduces size of tables Label Format Diagram


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Time to Live Processing Needed to support TTL since IP header not read First label TTL set to IP header TTL on entry to MPLS domain TTL of top entry on stack decremented at internal LSR

– If zero, packet dropped or passed to ordinary error processing (e.g. ICMP) – If positive, value placed in TTL of top label on stack and packet forwarded

At exit from domain, (single stack entry) TTL decremented – If zero, as above – If positive, placed in TTL field of Ip header and

Label Stack Appear after data link layer header, before network layer header Top of stack is earliest (closest to network layer header) Network layer packet follows label stack entry with S=1 Over connection oriented services

– Topmost label value in ATM header VPI/VCI field Facilitates ATM switching

– Top label inserted between cell header and IP header – In DLCI field of Frame Relay – Note: TTL problem

Position of MPLS Label Stack

FECs, LSPs, and Labels Traffic grouped into FECs Traffic in a FEC transits an MLPS domain along an LSP Packets identified by locally significant label At each LSR, labelled packets forwarded on basis of label.

– LSR replaces incoming label with outgoing label Each flow must be assigned to a FEC Routing protocol must determine topology and current conditions so LSP can be

assigned to FEC – Must be able to gather and use information to support QoS


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LSRs must be aware of LSP for given FEC, assign incoming label to LSP, communicate label to other LSRs

Topology of LSPs Unique ingress and egress LSR

– Single path through domain Unique egress, multiple ingress LSRs

– Multiple paths, possibly sharing final few hops Multiple egress LSRs for unicast traffic Multicast

Route Selection Selection of LSP for particular FEC Hop-by-hop

– LSR independently chooses next hop – Ordinary routing protocols e.g. OSPF – Doesn’t support traffic engineering or policy routing

Explicit – LSR (usually ingress or egress) specifies some or all LSRs in LSP for given

FEC – Selected by configuration,or dynamically

Constraint Based Routing Algorithm Take in to account traffic requirements of flows and resources available along hops

– Current utilization, existing capacity, committed services – Additional metrics over and above traditional routing protocols (OSPF)

Max link data rate Current capacity reservation Packet loss ratio Link propagation delay

Label Distribution Setting up LSP Assign label to LSP Inform all potential upstream nodes of label assigned by LSR to FEC

– Allows proper packet labelling – Learn next hop for LSP and label that downstream node has assigned to FEC

Allow LSR to map incoming to outgoing label Real Time Transport Protocol TCP not suited to real time distributed application

– Point to point so not suitable for multicast – Retransmitted segments arrive out of order – No way to associate timing with segments

UDP does not include timing information nor any support for real time applications Solution is real-time transport protocol RTP


SCE 80 ECE

5.8 RTP ARCHITECTURE Close coupling between protocol and application layer functionality

– Framework for application to implement single protocol Application level framing Integrated layer processing

Application Level Framing Recovery of lost data done by application rather than transport layer

– Application may accept less than perfect delivery Real time audio and video Inform source about quality of delivery rather than retransmit Source can switch to lower quality

– Application may provide data for retransmission Sending application may recompute lost values rather than storing them Sending application can provide revised values Can send new data to “fix” consequences of loss

Lower layers deal with data in units provided by application – Application data units (ADU)

Integrated Layer Processing Adjacent layers in protocol stack tightly coupled Allows out of order or parallel functions from different layers

5.9 RTP ARCHITECTURE DIAGRAM

RTP Data Transfer Protocol Transport of real time data among number of participants in a session, defined by:

– RTP Port number UDP destination port number if using UDP

– RTP Control Protocol (RTCP) port number Destination port address used by all participants for RTCP transfer

– IP addresses Multicast or set of unicast

Multicast Support Each RTP data unit includes:


SCE 81 ECE

Source identifier Timestamp Payload format

Relays Intermediate system acting as receiver and transmitter for given protocol layer Mixers

– Receives streams of RTP packets from one or more sources – Combines streams – Forwards new stream

Translators – Produce one or more outgoing RTP packets for each incoming packet – E.g. convert video to lower quality

RTP Header

RTP Control Protocol (RTCP) RTP is for user data RTCP is multicast provision of feedback to sources and session participants Uses same underlying transport protocol (usually UDP) and different port number RTCP packet issued periodically by each participant to other session members

RTCP Functions QoS and congestion control Identification Session size estimation and scaling Session control

RTCP Transmission Number of separate RTCP packets bundled in single UDP datagram

Sender report Receiver report


SCE 82 ECE

Source description Goodbye Application specific

RTCP Packet Formats

Packet Fields (All Packets) Version (2 bit) currently version 2 Padding (1 bit) indicates padding bits at end of control information, with number of octets

as last octet of padding Count (5 bit) of reception report blocks in SR or RR, or source items in SDES or BYE Packet type (8 bit) Length (16 bit) in 32 bit words minus 1 In addition Sender and receiver reports have:

Synchronization Source Identifier Packet Fields(SenderReport) Sender Information Block NTP timestamp: absolute wall clock time when report sent RTP Timestamp: Relative time used to create timestamps in RTP packets Sender’s packet count (for this session) Sender’s octet count (for this session)


SCE 83 ECE

Reception Report Block SSRC_n (32 bit) identifies source refered to by this report block Fraction lost (8 bits) since previous SR or RR Cumulative number of packets lost (24 bit) during this session Extended highest sequence number received (32 bit) Least significant 16 bits is highest RTP data sequence number received from SSRC_n Most significant 16 bits is number of times sequence number has wrapped to zero Interarrival jitter (32 bit) Last SR timestamp (32 bit) Delay since last SR (32 bit) Receiver Report Same as sender report except:

Packet type field has different value No sender information block

Source Description Packet Used by source to give more information 32 bit header followed by zero or more additional information chunks E.g.: 0 END End of SDES list 1 CNAME Canonical name 2 NAME Real user name of source 3 EMAIL Email address

Goodbye (BYE) Indicates one or more sources no linger active

Confirms departure rather than failure of network Application Defined Packet Experimental use For functions & features that are application specific


SCE 84 ECE

UNIT-01

HIGH SPEED NETWORKS PART-A 1. What is ATM?[MAY/JUNE-2012]

Asynchronous Transfer Mode (ATM) is a method for multiplexing and switching that supports a broad range of services. ATM is a connection-oriented packet switching technique that generalizes the notion of a virtual connection to one that provides quality-of-service guarantees. 2. What are the main features of ATM? The service is connection-oriented, with data transfer over a virtual circuit. The data is transferred in 53 byte packets called cells. Cells from different VCs that occupy the same channel or link are statistically

multiplexed. ATM switches may treat the cell streams in different VC connections unequally over

the same channel in order to provide different qualities of services (QOS). 3. What are the layers/plane of BISDN reference model? User plane. Control plane. Layer management plane. Plane management plane.

4. Define MPLS?

Multi Protocol Label Switching is to standardize a label switching paradigm that integrates layer 2 switching with layer 3 routing. The device that integrates routing and switching functions is called a Label Switching Router (LSR). 5. What is called frame relay?

Frame relay is a connection oriented data transport service for public switched networks. The frame relay protocols are modification of X.25 standards. 6. What are the advantages of DQDB MAC protocol? It is very efficient There is no loss of capacity due to collision The head station continuously generates an idle frame

7. Define VPI & VCI

The Virtual Path Identifier (VPI) constitutes a routing field for the network while the Virtual Channel Identifier (VCI) is used for the routing to and from the end user.

8. Mention the High Speed LANs Fast Ethernet Gigabit Ethernet Fibre Channel High Speed Wireless LANs.


SCE 85 ECE

9. What are the requirements for wireless LANs?[]MAY/JUNE-2014

Throughput Number of nodes Service Area Battery Power Handoff/roaming Dynamic Configuration.

10. What are the types of Ethernet? Classical Ethernet Fast Ethernet 10Mbps Ethernet Gigabit Ethernet 10-Gpbs Ethernet.

11. Define VPN MPLS provides an efficient mechanism for supporting Virtual Private Network (VPNs).With a VPN, the traffic of a given enterprise or group passes transparently through an internet providing performance guarantees and security. 12. Define ISDN?

The integrated services digital network is to provide a unique user network Interface (UNI) for the support of the basic set of narrow band (NB) services that is voice and low speed data thus providing a narrowband integrated access.

13. What are the features of an ISDN? Standard user network interface (UNI). Integrated digital transport. Service integration. Intelligent network services.

14. What are the services of LAPD? Acknowledgement information transfer service. Unacknowledgement information transfer service.

15. Define frame relay. A form of packet switching based on the use of variable-length link-layer frames. There is no network layer, and many of the basic functions have been streamlined or eliminated to provide for greater throughput. 16. What are the traffic parameters of connection-oriented services? Peak Cell Rate (PCR) Sustained Cell Rate (SCR) Initial Cell Rate (ICR). Cell Delay Variation Tolerance (CDVT). Burst Tolerance (BT). Minimum Cell Rate (MCR).


SCE 86 ECE

17. What are the quality service (QoS) parameters of connection-oriented services? Cell Loss Ratio (CLR). Cell Delay Variation (CDV). Peak-to-Peak Cell Delay Variation (Peak-to-Peak CDV). Maximum Cell Transfer Delay (Max CTD). Mean Cell Transfer Delay (Mean CTD).

18. Types of delays encountered by cells Packetization delay (PD) at the source. Transmission and propagation delay (TD). Queuing delay (QD) at each switch. Affixed processing delay (FD) at each switch. A jitter compression or depacketization delay (DD) at the destination.

19. What is the datalink control functions provided by LAPF? Frame delimiting, alignment & transparency. Frame multiplexing/demultiplexing using the address field. Inspection of the frame to ensure that it consist of an integer no. of octets prior to zero

bit insertion or following zero bit extraction. Inspection of the frame to ensure that it is neither too long nor too short. Detection of transmission errors. Congestion control functions.

20. Difference b/w AAL ¾ & AAL 3/5

AAL 3/4 AAL 3/5 I

n this MID field is used to multiplex diff streams of data on the same virtual ATM connection.

A 10 bit CRC is provided for each SAR PDU.

In this 8 ATM octets per AAL SDU, 4 octets per cell.

In this MID field is assumed to that the higher layer software takes care of such multiplexing.

A 32 bit CRC protects the entire cpu’s PDU, provides strong protection against bit errors.

8 octets per AAL SDU, 0 octets per ATM cell.

21. What are the principles of ISDN ? Support voice and non-voice communication. Support switched and non switched application. Reliance on 64Kbps connection. Intelligence in the network.


SCE 87 ECE

22. Difference b/w Frame relay and X.25 packet switching.[NOV/DEC-2012]

Frame Relay X.25 Packet Switching

nd to End flow and error control.

ultiplexing and switching operations are carried out in layer 2(Data link layer).

ommon Channel Signalling.

ata rate -2Mbps.

op by Hop flow and error control.

ultiplexing and switching operations are carried out in layer 3(network layer).

nband Signalling

ata rate -64Mbps.

23. Give the neat sketch of ATM Protocol Architecture.

24. Draw the ATM Cell structure or Cell Format.[MAY/JUNE-2014,2013,NOV/DEC-2014]


SCE 88 ECE


SCE 89 ECE

UNIT-02 CONGESTION AND TRAFFIC MANAGEMENT

PART-A 1. What are the queuing models?[MAY/JUN-2013,APR/MAY-2010]

Two types of queing models are , Single server queue. Multi server queue.

2. Why Congestion Occurs in the networks?[MAY/JUN-2012]

The phenomenon of congestion is a complex one, as in the subject of congestion control, congestion noccurs when the number of packetsb being transmitted through a network begins to approach the packet handling capacity of the network. 3. What is meant by the term congestion in networks?[MAY/JUN-2013]

The objective of the congestion control is to maintain the number of packets within the network is known as congestion in the network.

4. State Kendall’s notation.[APR/MAY-2011,NOV/DEC-2013]

Kendall’s notation is X/Y/N, where X refers to the distribution of the interarrival times, Y refers to the distribution of service times, and N refers to the number of servers. The most common distributions are denoted as follows: G = General distribution of interarrival times or service times

GI = General distribution of interarrival times with the restriction that Interarrival times are independent.

M = Negative exponential distribution D = Deterministic arrivals or fixed-length service. Thus, M/M/1 refers to a single-server queuing model with poisson arrivals (Exponential interarrival times) and exponential service times. 5. What is meant by congestion control technique?

Congestion Avoidance: It is the procedure used at beginning stage of congestion to minimize its effort. This procedure initiated prior to or at point A. This procedure prevent congestion from progressing to point B. Techniques, Back pressure Choke packet Implicit congestion Signalling Explicit Congestion Signalling.

6. Define Backward explicit congestion notifivation?[NOV/DEC-2012]

The BECN bit is part of the Address field in the Frame Relay frame header. DCE devices set the value of the BECN bit to 1 in frames traveling in the opposite direction of frames with their FECN bit set. This informs the receiving DTE device that a particular path through the network is congested.


SCE 90 ECE

7. What is single server queue?[MAY/JUN-2014] The control element of the system is a server, which provides some service to items. If

the server is idle an item is served immediately. Otherwise an arriving items joins awaiting line. Dispatching Discipline Arrival Departure

Residence Time 8. Define committed burst size (BC) It is defined as the maximum number of bits in a predefined period of time that the network is committed to transfer with out discarding any frames. 9. Define committed information rate (CIR) CIR is a rate in bps that a network agrees to support for a particular frame mode connection. Any data transmitted in excess of CIR is vulnerable to discard in event of congestion. CIR < Access rate 10. Define excess burst size (Be) It is defined as the maximum number of bits in excess of BC that a user can send during a predefined period of time. The network is committed to transfer these bits if there is no congestion. Frames with Be have lower probability to transfer than frames with BC. 11. Define access rate. For every connection in frame relay network, an access rate (bps) is defined. The access rate actually depends on bandwidth of channel connecting user to network. 12. Write Little’s formula.[NOV/DEC-2009] Little’s formula is defined as the product of item arrive at a rate of λ, and Served time of items Tr (or) product of item arrive at a rate of λ and waiting time of an items Tw. It is given as, r = λ Tr (or) w = λ Tw

13. List out the model characteristics of queuing models. Item population. Queue size Dispatching discipline Service pattern

14. List out the fundamental task of a queuing analysis. Queuing analysis as the following as a input information. Arrival rate Service rate Number of servers

Provide as output information concerning: Items waiting

Waiting line(Queue) Server


SCE 91 ECE

Waiting time Items queued Residence time

15. List out the assumptions for single server queues. Poisson arrival rate. Dispatching discipline does not give preference to items based on service times Formulas for standard deviation assume first-in, first-out dispatching. No items are discarded from the queue.

16. List out the assumptions for Multiserver queues. Poisson arrival rate. Exponential service times All servers equally loaded. All servers have same mean service time. First-in, first-out dispatching. No items are discarded from the queue.

17. State Jackson’s theorem. Jackson’s theorem can be used to analyse a network of queues. The theorem is based on three assumptions: 1. The queuing network consists of m nodes, each of which provides an independent exponential service. 2. Items arriving from outside the system to any one of the nodes arrive with a poisson rate. 3. Once served at a node, an item goes (immediately) to one of the other nodes with a fixed probability, or out of the system. 18. Define Arrival rate and service rate. Arrival Rate: The rate at which data enters into a queuing system i.e., inter arrival rate. It is indicated as λ.

Service Rate: The rate at which data leaves the queuing system i.e., service rate. It is indicated as μ.

19.How does frame relay report congestion? When the particular portion of the network is heavily congestion. It is

Desirable to route packets around rather than through the area of congestion.


SCE 92 ECE

UNIT-03

TCP AND ATM CONGESTION CONTROL

PART-A 1. Define congestion.

Excessive network or internetwork traffic causing a general degradation of service.

2. Define congestion control.[MAY/JUNE-2014] A method to limit the total amount of data entering the network, to amount of data that network can carry. 3. List out the TCP implementation policy option.

Send policy Deliver policy Accept policy Retransmit policy Acknowledge policy

4. List out the three retransmit strategies in TCP traffic control?[MAY/JUNE-2014]

First-only Batch Individual

5. Explain about the congestion control in a TCP/IP based internet implementation task.

IP is connectionless, stateless protocol that includes no provision for detecting, much less controlling congestion.

TCP provides only end-to-end flow control and deduce the presence of congestion.

There is no cooperative, distributed algorithm to bind together the various TCP entities.

6. list out retransmission timer management techniques[NOV/DEC-2010]

RTT variance estimation. Exponential RTO back off Karn’s algorithm.

7. Write down the window management techniques.[NOV/DEC-2013]

Slow start. Dynamic window sizing on congestion. Fast retransmit Fast recovery Limited transmit.

8. Define binary exponential back off.[NOV/DEC-2012]

A simple technique for implementing RTO backoff is to multiply the RTO for a segment by a constant value for each retransmission.


SCE 93 ECE

RTO = q * RTO ………. (1) The equation causes RTO a grow exponentially with each retransmission. The most

commonly used value of q is 2. 9.State the condition that must be met for a cell to conform.

In case of ATM, the information flow on each logical connection is organized into fixed-size packets called cells.

Cells should arrive with in theoretical arrive time but with in CDVT (limitation) cell is conformed.

10.What are the mechanisms used in ATM traffic control to avoid congestion condition?[MAY/JUNE-2015]

Resource management. Connection admission control Usage parameter control Traffic shaping

11.How is times useful to control congestion in TCP? The value of RTO (Retransmission time out) have a critical effect on TCP’s reaction to

congestion. Hence by calculating RTO effectively congestion can be controlled.

12.What is the difference between flow control and congestion control? Flow control: The transmitter should not overwhelm the receiver so flow control

is performed. Congestion control: It aim to limit the total amount of data entering the network,

to amount of data that network can carry.

13. What is reactive congestion control and preventive congestion control. Reactive congestion control: Whenever a packet discard, occur due to severe

congestion, some control mechanism is needed to recover from network collapse these mechanism is reactive congestion control.

Preventive congestion control: Mechanism to avoid congestion before it occurs. 14. Why congestion control is difficult to implement in TCP? The end system is expected to exercise flow control upon the source end system at a higher layer. Thus it is difficult to implement in TCP. 15. What are the accept policies used in TCP traffic control? Accept policy: a). In-order policy b). In –window policy. 16. What is meant by silly window syndrome? If frequently data’s are send as small segment, the response will be speed in sender side but it cause degradation in performance. This degradation is called silly window syndrome. 17. What is meant by cell insertion time? Cell insertion time is the time taken to insert a single cell on to the network.


SCE 94 ECE

18. What are the mechanisms used in TCP to control congestion? TCP congestion control mechanism: a). RTO timer management b). window management 19. What is meant by open loop and closed loop control in ABR mechanism?

Open loop control: If there is no feedback to the source concerning congestion, this approach is called open loop control.

Closed loop control: ABR has feedback to the source concerning congestion; this approach is called closed loop control. 20. What is meant by allowed cell rate (ACR)?[APR/MAY-2010] Allowed cell rate: The current rate at which source is permitted to send or transmit cell in ABR mechanism is called allowed cell rate. 21. Define Behavior Class Selector (BCS) Behaviour Class Selector (BCS): BCS enables an ATM network to provide different service levels among UBR connections by associating each connection with one of a set of behaviour class. 22. What is cell delay variation?

In ATM cell network voice & video signals can be digitized & transmitted as a system of cells. A key requirement especially for voice is that the delay across the network be short. ATM is designed to minimize the processing & transmission overhead to the networks. So that very fast cell switching & routing is possible. 23. Why retransmission policy essential in TCP?

TCP maintains a queue of segments that have been sent but not yet acknowledged. The TCP specification states that TCP will retransmit a segment. If it fails to receive an acknowledge within a given time. A TCP implement may employ one of three retransmission strategies.

(i) First only (ii) Batch

(iii) Individual 24. Why congestion control in a tcp/ip internet is complex?

The task is difficult one becoz of the following factor (i)IP is a connectionless stateless protocol that includes no provision for detecting much less controlling congestion. (ii)TCP provides only end-to-end flow control. (iii)There is no co-operative distributed algorithm. 23. Write relationship b/w throughput & TCP window size ‘W’.

S = 1 for W> RD/4 4W /RD for W< RD/4

Where W TCP window size (octets) R Data rate at TCP source available to a given TCP connection. D Propagation delay b/w TCP source & destination over a given TCP Connection.

26. Define ABR[MAY/JUNE-2013] ABR is the available bit rate. ABR specifies a Peak Cell Rate (PCR) that it requires.

The network allocates resources so that all ABR applications receive at least their MCR


SCE 95 ECE

capacity. The ABR mechanism uses explicit feedback to sources to assure that capacity is facility allocated.

27. Define CBR (Constant Bit Rate)

The CBR service is perhaps the simplest to define. It is used by applications that require a fixed data rate that is continuously available during the connection lifetime & a relatively tight upper bound on transfer delay. CBR is commonly used for uncompressed audio & video information.

28. Write the examples for CBR.

Video conferencing Interactive audio Audio/video distribution Audio/video retrieval


SCE 96 ECE

UNIT-04 INTEGRATED AND DIFFERENTIATED SERVICE

PART-A 1. Write down the two different, complementary IETF Standards traffic management Frameworks?

Integrated services Differentiated services

2. Write down the current traffic demand viewed by the IS provider?

Limits the demand that is satisfied to that which can be handled by the current capacity of the network. Reserves resources within the domain to provide a particular QoS to particular

portions of the satisfied demand. 3. Explain about differentiated services?

A DS framework does not attempt to view the total traffic demand in any overall or integrated sense, nor does it attempt to reserve network capacity in advance. In DS framework, traffic is classified into a number of traffic groups. Each groups is labeled appropriately, and the service provided by network elements depends on group membership, with packets belonging to different groups being handled differently.

4. What are the requirements for inelastic traffic?[APR/MAY-2008]

Throughput Delay Jitter Packet loss

5. Give some applications that come under elastic traffic.[NOV/DEC-2013]

E-Mail (SMTP) – Quite insensitive to changes in delay. File transfer (FTP) – The delay to be proportional to the file size and sensitive

to changes in throughput. Network management (SNMP) – To get through with minimum delay

increases with increased congestion. Remote Logon and Web Access (TELNET and HTTP) – These are called as

Interactive applications are quite sensitive to delay.

6. State the drawbacks of FIFO queering discipline?[APR/MAY-2008] No special treatment is given to packets from flows that are of higher priority

(or) are more delay sensitive. If a number of packets from different flows are ready to forward, they are handled strictly in FIFO order.

If a number of smaller packets are queued behind a long packet, then FIFO Queuing results in a larger average delay per packet than if the shorter packets were transmitted before the longer packet. In general, flows of larger packets get better service.

A greedy TCP connection can crowd out more altruistic connections. If congestion occurs and one TCP connection fails to back off, other

Connections along the same path segment must back off.


SCE 97 ECE

7. Distinguish between inelastic and elastic traffic?[NOV/DEC-2009]

S.No Elastic traffic Inelastic traffic

1

Elastic traffic is that which can adjust , over wide ranges, to changes in delay and throughput across an internet and still meet the needs of its applications

Inelastic traffic does not easily adapt, if at all, to changes in delay and throughput across an internet.

2

Example is electronic mail(SMTP),file transfer(FTP), Web access(HTTP),Network management(SNMP)

Prime examples is real-time traffic (Voice chat, Tele conferencing)

8. Define the format of DS field?

Packets are labeled for service handling by means of the DS field, which is placed in the type of service field of an IPv4 header or the traffic class field of the IPv6 header.

RFC 2474 defines the DS field as having the following format: the leftmost 6 bits form a DS code point and the rightmost 2 bits are currently unused. The DS codepoint is the DS label used to classify packets for differentiated services. 9. Define DS code point. A specified value of 6 bit DS code point portion of the 8 bit DS field in the IP header which indicate to which class packets belongs and its drop precedence. 10. What is meant by traffic conditioning agreement? An agreement that specify rules that are to apply for packets selected by the classifier. Control functions performed in TCA are metering, marking, shaping and dropping. 11. Define DS boundary node. A DS node that connects one DS domain to the node in another domain. 12. Define DS interior node. A node in DS domain, which is not the boundary node is called DS interior node. 13. Define DS node. A router that supports DS policies is called as DS node. A host system that uses DS for application is also called as DS node. 14. Write down the two routing mechanism use in ISA.

Routing algorithm- Decreases local congestion, reduces delay. Packet discard- Most recent packet is discarded, sending TCP entity back off,

Reduces load. 15. List out the ISA components?

Reservation protocol. Admission control Management agent.


SCE 98 ECE

Routing protocol 16. List out the two principal functionality areas that accomplish forwarding packets in the router.

Classifier and route selection. Packet scheduler.

17. Define TSpec. ISA service for a flow of packets is defined on two levels.

A number of general categories of service are provided, each of which provides a certain general type of service guarantees.

Within each category, the service for a particular flow is specified by the values of certain parameters.

Together, these values are referred to as a traffic specification (TSpec) 18. List out the categories of service in ISA.

Guaranteed service Controlled load service Best effort service

19. List out the advantages of ISA.[APR/MAY-2010]

Many traffic sources can easily and accurately be defined by a token bucket scheme.

The token bucket scheme provides a concise description of the load to be imposed by a flow, enabling the service to determine easily the resource requirement.

The token bucket scheme provides the input parameters to a policing function. 20. Define delay jitter. The delay jitter is the maximum variation in delay experienced by packets in a single session. 21. What is meant by differentiated service?[MAY/JUNE-2012]

It does not attempt to view the total traffic demand in integrated sense. It does not reserve network capacity in advance. It provides different level of QoS to different traffic flows.

22. What is meant by integrated service? The IS provider

Views the totally of current traffic demand. Limits the demand with respect to the current capacity handled by the network. Reserve resources with in the domain to provide a particular QOS guaranteed.

23. Define global synchronization. Due to packet discard during congestion, many TCP connections entered slow start at the same time. As a result, the network is unnecessarily under utilized for some time. The TCP connections which entered into slow start, will come out of slow start at about same time causing congestion again. This phenomenon is called global synchronization.


SCE 99 ECE

24. What are the design goals of RED algorithm?[MAY/JUNE-2013] Congestion avoidance Global synchronization avoidance

UNIT-05

PROTOCOLS FOR QOS SUPPORT PART-A 1. What is meant by soft state in RSVP?[APR/MAY-2015] RSVP use connectionless approach, each intermediate router maintain state information about nature of flow, that will be refreshed by end system at predetermined amount of time. This is called soft state. 2. Define session in RSVP? Once a reservation is made at a router by a particular destination, the router considers this as a session and allocates resources for the life of that session. Session is defined by, Session: Destination IP address IP protocol identifier. 3.Define label switched swapping in MPLS.[NOV/DEC-2012] The basic operation of looking up an incoming label to determine the outgoing label and forwarding is called Label Swapping. 4. What are the features of RSVP?[MAY/JUNE-2013]

1. Performs resource reservations for unicast and multicast applications 2. Requests resource in one direction from a sender to a receiver 3. Requires the receiver to initiate and maintain the resource reservation. 4. Maintains soft state at each intermediate router 5. Does not require each router to be RSVP capable 6. Supports both IPv4 and IPv6.

5. Define soft state When a state is not refreshed within a certain timeout, the state is deleted. The type of

state that is maintained by a timer is called a soft state.

6. What does RTCP provide to the sources?[NOV/DEC-2013] RTCP provides:

a) Quality of service and congestion control b) Identification c) Session size estimation d) Session control

7.Define The Format Of RTP Leader

V P X CC M PLT SQNO TIME STAMP


SCE 100 ECE

SYNCHRONIZATION SOURCE IDENTIFIERS (SSRC) CONTRIBUTING SOURCE IDENTIFIER (CSRC) . . . . CSRC IDENTIFIER

e) V Version (2 bit) f) P padding (1 bit) g) X Extension (1 bit) h) CC CSRC count (4 bit) i) M Marker (1 bit) j) PLT Payload type (7 bit) k) SQNO sequence no. (16 bit) l) Time Stamp (32 bit)

8.List out the characteristics of MPLS. MPLS characteristics that ensure its popularity are:

a) Connection-oriented QOS support b) Traffic engineering c) Virtual private network(VPN) support d) Multi protocol support

9. What is Label Stacking?[APR/MAY-2015]

The Stack Entries appear after the data i\link layer headers,but before network layer headers.The top of the label stack appears earliest in the packet and the bottom appears latest. The network layer follows the label packetstack entry which has the s bit set. In the data link frame, such as for PPP, the label stack appears between trhe IP header and data link header. 10.Define QOS[MAY/JUNE-2012]

It refers to the properties of a network that contributes to the degree of satisfaction that users perceive, relative to the network’s performance. 11.List QOS Parameters.[NOV/DEC-2014] Capacity, or Data rate Latenc, or delay Jitter Traffic lose

12 Define RSVP?[MAY/JUNE-2011]

Resource Reservation Protocol was designed as an IP signaling protocol for the integrated services model. RSVP can be used by a host to request a specific QoS resource for a particular flow and by a router to provide the requested QoS along the paths by setting up appropriate states.

13. What is meant by integrated layer processing in RTP? In TCP/IP each layer processed sequentially, whereas in integrated layer


SCE 101 ECE

processing, adjacent layers are tightly coupled and they function parallel. 14. What is the function of RTP relays and give its types? A relay operating at a given protocol layer is an intermediate system that acts as both a destination and a source in a data transfer. 15. What is the function of mixer and translator in RTP? Mixer: It is source of synchronization. It receives stream of RTP packets from one or more sources. Combines these streams and forwards a new RTP packet stream to one or more destinations. Translator: It produces one or more outgoing RTP packets for each incoming packets. It change the format of the data that suite to transfer from one domain to another. 16.What are the resources used by an integrated service model?

Integrated service model requires resources such as bandwidth and buffers to be explicitly reserved for a given dataflow to ensure that the application receives its requested QoS 17. What do you mean by guaranteed service?

The guaranteed service in the internet can be used for applications that require real time service delivery. For this application data that is delivered to the application after a certain time is generally considered worthless. Thus guaranteed service has been designed to provide a frame bound on the end to end packet delay for a flow.

UNIVERSITY QUESTION BANK

UNIT-01 HIGH SPEED NETWORKS

PART-A

1. What is ATM?[MAY/JUNE-2012] 2. What are the main features of ATM? 3. What are the layers/plane of BISDN reference model? 4. Define MPLS? 5. What is called frame relay? 6. What are the advantages of DQDB MAC protocol? 7. Define VPI & VCI

8. Mention the High Speed LANs 9. What are the requirements for wireless LANs?[]MAY/JUNE-2014 10. What are the types of Ethernet?

11. Define VPN 12. Define ISDN? 13. What are the features of an ISDN? 14. What are the services of LAPD? 15. Define frame relay. 16. What are the traffic parameters of connection-oriented services? 17. What are the quality service (QoS) parameters of connection-oriented services? 18. Types of delays encountered by cells 19. What is the datalink control functions provided by LAPF? 20. Difference b/w AAL ¾ & AAL 3/5 21. What are the principles of ISDN ? 22. Difference b/w Frame relay and X.25 packet switching.[NOV/DEC-2012] 23. Give the neat sketch of ATM Protocol Architecture. 24. Draw the ATM Cell structure or Cell Format.[MAY/JUNE-2014,2013,NOV/DEC-2014]

PART-B 1. Discuss the various ATM service categories.[MAY/JUNE-2015,2013] 2. Explain the ATM Protocol architecture with a neat block diagram.[MAY/JUNE-2015,2013] 3. Explain the Frame Relay Networks with suitable diagram.[MAY/JUNE-2012] 4. Draw IEEE 802.11 architecture and Protocol architecture.[MAY/JUNE2013,NOV/DEC-2013] 5.Discuss the relevance of CSMA/CD in gigabit ethernets.[]MAY/JUNE-2012NOV/DEC-2012 6.Explain in detail about Fiber Channel.

UNIT-02

CONGESTION AND TRAFFIC MANAGEMENT

PART-A 1. What are the queuing models?[MAY/JUN-2013,APR/MAY-2010] 2. Why Congestion Occurs in the networks?[MAY/JUN-2012] 4. State Kendall’s notation.[APR/MAY-2011,NOV/DEC-2013] 5. What is meant by congestion control technique? 6. Define Backward explicit congestion notifivation?[NOV/DEC-2012] 7. What is single server queue?[MAY/JUN-2014] 8. Define committed burst size (BC) 9. Define committed information rate (CIR) 10. Define excess burst size (Be) 11. Define access rate. 12. Write Little’s formula.[NOV/DEC-2009] 13. List out the model characteristics of queuing models. 14. List out the fundamental task of a queuing analysis. 15. List out the assumptions for single server queues. 16. List out the assumptions for Multiserver queues. 17. State Jackson’s theorem. 18. Define Arrival rate and service rate. 19.How does frame relay report congestion?

PART-B

1. Explain Queuing theory.[APR/MAY-2015] 2. Explain Queuing Analysis and its types.[APR/MAY-2015] 3. Explain Traffic Management In Congestion Control.[MAY/JUNE-2012,NOV/DEC-2012] 4. Explain the Congestion Control Mechanisms.[NOV/DEC-2012]

UNIT-03 TCP AND ATM CONGESTION CONTROL

PART-A

1. Define congestion. 2. Define congestion control.[MAY/JUNE-2014] 3. List out the TCP implementation policy option. 4. List out the three retransmit strategies in TCP traffic control?[MAY/JUNE-2014] 5. Explain about the congestion control in a TCP/IP based internet implementation task. 6. list out retransmission timer management techniques[NOV/DEC-2010] 7. Write down the window management techniques.[NOV/DEC-2013] 8. Define binary exponential back off.[NOV/DEC-2012] 9. State the condition that must be met for a cell to conform. 10.What are the mechanisms used in ATM traffic control to avoid congestion condition?[MAY/JUNE-2015] 11.How is times useful to control congestion in TCP? 12.What is the difference between flow control and congestion control? 13. What is reactive congestion control and preventive congestion control. 14. Why congestion control is difficult to implement in TCP? 15. What are the accept policies used in TCP traffic control? 16. What is meant by silly window syndrome? 17. What is meant by cell insertion time? 18. What are the mechanisms used in TCP to control congestion? 19. What is meant by open loop and closed loop control in ABR mechanism? 20. What is meant by allowed cell rate (ACR)?[APR/MAY-2010] 21. Define Behavior Class Selector (BCS) 22. What is cell delay variation? 23. Why retransmission policy essential in TCP? 24. Why congestion control in a tcp/ip internet is complex?

25.Write relationship b/w throughput & TCP window size ‘W’. 26. Define ABR[MAY/JUNE-2013] 27. Define CBR 28. Write the examples for CBR.

PART-B 1. Explain TCP Flow Control. 2. Explain the TCP Congestion Control with neat diagrams.[MAY/JUNE-2013] 3. Explain Retransmission and Timer Management Techniques.[NOV/DEC-2013] 4. Explain five important techniques in window management. 5. Explain Traffic And Congestion Control in ATM and its requirements.[NOV/DEC-2013] 6. Explain the ATM traffic – related attributes.[NOV/DEC-2012] 7. Explain in detail ABR traffic management.[MAY/JUNE-2014]

UNIT-04 INTEGRATED AND DIFFERENTIATED SERVICE

PART-A

1. Write down the two different, complementary IETF Standards traffic management Frameworks? 2. Write down the current traffic demand viewed by the IS provider? 3. Explain about differentiated services? 4. What are the requirements for inelastic traffic?[APR/MAY-2008] 5. Give some applications that come under elastic traffic.[NOV/DEC-2013] 6. State the drawbacks of FIFO queering discipline?[APR/MAY-2008] 7. Distinguish between inelastic and elastic traffic?[NOV/DEC-2009] 8. Define the format of DS field? 9. Define DS code point. 10. What is meant by traffic conditioning agreement? 11. Define DS boundary node. 12. Define DS interior node. 13. Define DS node. 14. Write down the two routing mechanism use in ISA. 15. List out the ISA components? 16. List out the two principal functionality areas that accomplish forwarding packets in the router. 17. Define TSpec. 18. List out the categories of service in ISA. 19. List out the advantages of ISA.[APR/MAY-2010] 20. Define delay jitter. 21. What is meant by differentiated service?[MAY/JUNE-2012] 22. What is meant by integrated service? 23. Define global synchronization. 24. What are the design goals of RED algorithm?[MAY/JUNE-2013]

PART-B 1. Explain the block diagram for Integrated Services Architecture,and give details about components.[ MAY/JUNE-2014,NOV/DEC-2013] 2. Explain the services offered Preferred by ISA [APR/MAY-2015] 3. Explain the various queuing disciplines in ISA .[MAY/JUNE-2013,NOV/DEC-2013,2012] 4. Explain the RED algorithm .[APR/MAY-2015,MAY/JUNE-2013 ,NOV/DEC-2013] 5. Explain Differentiated services briefly.[APR/MAY-2015,MAY/JUNE-2013,2014] 6. Write a short notes on DS per hop behaviour[NOV/DEC-2013].

UNIT-05 PROTOCOLS FOR QOS SUPPORT

PART-A

1. What is meant by soft state in RSVP?[APR/MAY-2015] 2. Define session in RSVP? 3.Define label switched swapping in MPLS.[NOV/DEC-2012] 4. What are the features of RSVP?[MAY/JUNE-2013] 5. Define soft state 6. What does RTCP provide to the sources?[NOV/DEC-2013] 7.Define The Format Of RTP Leader 8.List out the characteristics of MPLS. 9. What is Label Stacking?[APR/MAY-2015] 10.Define QOS[MAY/JUNE-2012] 11.List QOS Parameters.[NOV/DEC-2014] 12 Define RSVP?[MAY/JUNE-2011] 13. What is meant by integrated layer processing in RTP? 14. What is the function of RTP relays and give its types? 15. What is the function of mixer and translator in RTP? 16.What are the resources used by an integrated service model? 17. What do you mean by guaranteed service?

PART-B 1. Explain the Characteristics , goals of RSVP & the types of data flow[APR/MAY-2014,2015] 2. Explain the reservation style of the RSVP in detail.[NOV/DEC-2013,2012] 3. Explain the RSVP protocol operation and Mechanisms.[MAY/JUNE-2014] 4. Explain the MLPS architecture in detail[MAY/JUNE-2015,2013,NOV/DEC-2012] 5. Explain the RTP protocol architecture.[MAY/JUNE-2013,2015,NOV/DEC-2012] 6. Explain the RTP data transfer protocol.[NOV/DEC-2012]

Anna University Of Technology , Chennai

B.E/B.TECH DEGREE EXAMINATION , MAY/JUNE 2012

Seventh Semester

Electronics and Communication Engineering

CS 2060/CS 807/EC1009 – HIGH SPEED NETWORKS

(Regulation 2008)

Time : Three hours Maximum : 100 marks

Answer ALL qustions

Part – A (10 X 2 = 20 marks)

1. Define asynchronous transfer mode.

2. List the functions provided by AAL ¾ layer.

3. What are the advantages of packet over circuit switching?

4. Why congestion occurs in the networks?

5. What are the types of traffic management?

6. Define exponential RTO back off.

7. Define random early detection.

8. What is meant by FQ?

9. What are the goals of RSVP?

10. Define QOS and give any of its 2 parameters.

PART B – (5 X 16 = 80 marks)

11. (a) (i) Explain about frame relay networks in detail with suitable diagram. (8)

(ii) Explain in detail about fibre channel networks. (8)

(Or)

(b) (i) Describe in detail about Wifi and WiMax network application and

requirements. (8)

(ii) Explain about Gigabit Ethernet in detail with neat diagram. (8)

12. (a) (i) Explain in detail about frame relay congestion control technique. (8)

(ii) Explain about traffic management in packet switching. (8)

(Or)

(b) (i) Explain in detail about single server queues and its application. (8)

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(ii) Describe about effect of congestion. (8)

13. (a) (i) Explain in detail about KARN’s algorithm and window management.(8)

(ii) Explain about network management in detail with neat sketch. (8)

(Or)

(b) (i) Explain in detail about clock instability and jitter measurements. (10)

(ii) Explain about traffic management framework in detail. (6)

14. (a) Explain in detail about queuing disciplines : BRFQ, WFQ, GPS, and PS.

(Or)

(b) Explain about integrated service architecture and differentiated services in

detail with neat diagram.

15. (a) Explain in detail about RTCP architecture and RIP protocol details.

(Or)

(b) Discuss about protocols used for QOS support with neat diagram.

----------------------------------




Reg.No. :

Question Paper Code : 21293

B.E./B.TECH. DEGREE EXAMINATION , MAY/JUNE 2013

Seventh Semester

Electronics and Electronics Engineering

CS 2060 / CS 807 / EC 1009 – HIGH SPEED NETWORKS

(Common to Eighth Semester –Computer Science and Engineering)

(Regulation 2008)

(Common to PTCS 2060 High Speed Networks for B.E. (Part Time) Seventh Semester – ECE – Regulation 2009)

Time : 3 hours Maximum : 100 marks

Answer ALL questions

PART A – (10 X 2 = 20 marks)

1.Give few examples for High Speed networks.

2.Draw the ATM cell structure.

3.What is meant by the term “Congestion”in networks?

4.What are the types of queuing models?

5.What is exponential RTO backoff?

6.Define ABR and GFR?

7.Compare Integrated Services architecture and Differentiated Services

architecture.

8.What is significance of Random Early Detection technique?







9.What are the goals of RSVP?

10.List the main functions of RTP and RTCP?

PART B – (16 X 5 = 80 marks)

11. (a) (i) Explain ATM protocol architecture with a neat diagram. (8)(ii) Briefly explain ATM service categories. (8)

(Or)(b) (i) Explain in detail about 802.11 architecture. (10)

(ii) Write short notes on:(a) Wireless LANs.(b) Wi-Fi networks.(c) Wi-Max networks. (6)

12. (a) (i) Explain the Single Server Queuing model in detail. (10)

(ii) Discuss briefly the effects of congestion in networks. (6)

(Or)

(b) Write notes on congestion control used in :

(i) Packet Switching Networks.

(ii) Frame Relay Networks.

13. (a) (i) Explain TCP Congestion control in detail. (10)

(ii) Discuss KARN’s algorithm. (6)

(Or)

(b) (i) Explain ABR Traffic management in detail. (8)

(ii) Explain GFR Traffic management in detail. (8)

14. (a) (i) Briefly discuss the various queuing disciplines of integrated services. (10)





(ii) Discuss the advantages and downsides of integrated service

architecture. (6)

(Or)

(b) (i) Explain differentiated services architecture in detail. (10)

(ii) Explain the benefits of Random Early detection algorithm. (6)

15. (a) Explain the Following :

(i) RSVP. (10)

(ii) Multiprotocol label switching mechanism. (6)

(Or)

(b) Explain the following :

(i) RTP. (10)

(ii) RTCP. (6)

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Reg No :

Question Paper Code : 11263

B.E./B.Tech. DEGREE EXAMINATION , NONEMBER/DECEMBER 2012

Seventh Semester


CS 2060 / CS 807 / EC 1009 – HIGH SPED NETWORKS

(Common to Eighth Semester – Computer Science and Engineering)

(Regulation 2008)

(Common to PTCS High Speed Networks For B.E. (Part Time) Seventh Semester

Electronics and Communication Engineering – (Regulation 2009))

Time : Three hours Maximum : 100 marks


PART A – (10 X 2 = 20 marks)

1. Differentiate between frame relaying and X.25 packet switching service.

2. State the data link control functions provided by LAPF protocol.

3. List and explain the parameters for a single server queue.

4. What is meant by BECN?

5. State the mechanisms for supporting rate guarantees in GFR traffic.

6. What is meant by exponential RTO back off?

7. Give some applications that follow elastic traffic.

8. State the performance parameters that should be in the SLA for a DS document.

9. What is meant by soft state?

10. Explain label stacking in MPLS network.

PART B – (5 X 16 = 80 marks)

11. (a) (i) Explain the operation to AAL 1 and AAL ¾ with an example. (8)

(ii) Explain the working of an ATM error control algorithm. (8)

(Or)

(b) (i) Illustrate why CSMA/CD is not suitable for wireless LANs. (8)

(ii) Draw the 802.11 protocol stack and discuss the functions of PCF and DCF. (8)



12. (a) (i) Explain in detail the following congestion control techniques.

(1) Back pressure. (4)

(2) Choke packet. (4)

(3) Explicit congestion signalling. (4)

(ii) Explain the Kendall’s notation in detail. (4)

(Or)

(b) (i) Explain the single server queuing model and its applications. (8)

(ii) Explain about traffic rate management in frame relay networks. (8)

13. (a) (i) Explain about TCP window management in detail. (8)

(ii) Explain the RTF variance estimation using Jacobson’s algorithm in detail. (8)

(Or)

(b) (i) List and explain the ATM traffic parameter in detail. (8)

(ii) Explain the ATM ABR traffic management in detail. (8)

14. (a) (i) Explain the way in which ISA manages congestion and provides QOS

transport. (8)

(ii) Explain hit round fair queuing technique in detail. (8)

(Or)

(b) Explain the differentiated services operation and the traffic conditioning functions

in detail.

15. (a) (i) List and explain the three RSVP reservation styles in detail. (9)

(ii) Explain the MPLS operation in detail with a diagram. (7)

(Or)

(b) (i) Explain the RTP data transfer protocol architecture in detail. (8)

(ii) Explain the functions performed by the RTP control protocol and its packet types in

detail.



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Reg.no :

Question paper Code : 31293

B.E./B.Tech. DEGREE EXAMINATION , NOVEMBER/DECEMBER

2013

Seventh Semester


CS 2060/CS 807/EC 1009/10144 ECE 33 – HIGH SPEED NETWORKS

(Common to Eighth Semester – Computer Science and Engineering)

(Regulation 2008/2010)

(Also Common to PTCS 2060 – High Speed Networks for B.E. (Part-Time)

Seventh Semester – Electronics and Communication Engineering –

Regulation 2009)

Time : Three hours Maximum : 100

marks


PART A – (10 X 2 = 20 marks)

1. State the advantages of frame relay.

2. Is CSMA/CD used in gigabit LANS? Justify.

3. What is meant by Kendall’s notation?

4. Mention the congestion control techniques used in packet switching

networks.

5. Define peak cell rate.

6. List the TCP window management techniques.

7. State the characteristics of elastic traffic.

8. What is meant by controlled load service?

9. What is the need for RTCP?

10. What is meant by a flow descriptor?

PART B – (5 X 16 = 80 marks)


11. (a) (i) Explain the call control procedure in frame relay networks. (8)

(ii) Explain the various ATM service categories in detail. (8)

(Or)

(b) Explain the IEEE802.11 architecture in detail. Illustrate the functions

and combined operation of various protocol in MAC sub layer. (16)

12. (a) (i) Explain with an example the implementation of single server

queues. (8)

(ii) Explain in detail about the Jackson’s theorem. (8)

(Or)

(b) (i) Explain the effects of congestion in packet switching networks. (8)

(ii) Explain how congestion avoidance is done in a frame relay

networks. (8)

13. (a) (i) Explain the TCP timer management techniques in detail. (8)

(ii) Discuss in detail about the congestion control techniques followed

in ATM networks. (8)

(Or)

(b) (i) Explain in detail about ABR capacity allocation. (8)

(ii) Discuss in detail about ABR traffic control. (8)

14. (a) (i) Draw the Integrated service architecture and explain it in detail.

(10)

(ii) Explain the fair queuing in detail. (6)

(Or)

(b) (i) Explain in detail the way in which RED techniques overcomes

congestion. (8)

(ii) Write a notes on the DS per hop behaviour. (8)

15. (a) (i) Explain the reservation styles of the RSVP in detail. (8)

(ii) Explain the features of MPLS. (8)

(Or)


(b) (i) Explain the RTP protocol architecture in detail. (8)

(ii) Explain the functions and message types of the RTP control

protocol. (8)

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A Course Material on - Sasurie College of Engineering Sem 7/CS2060 H… · a course material on high speed networks by mr. m.shanmugharaj assistant professor ... cs2060 high speed

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