Transcript
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Advanced Internet Technologies, SS 2005 2.1
Advanced Internet Technologies
Chapter 2
ATM
Prof. Dr. Georg Carle
Chair for Computer Networks & Internet
Wilhelm-Schickard-Institute for Computer Science
University of Tübingen
http://net.informatik.uni-tuebingen.de/
carle@informatik.uni-tuebingen.de
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Advanced Internet Technologies, SS 2005 2.2
Basics of ATM
Introduction
Reference Model Higher Layers
Signaling, Routing
IP over ATM
LAN over ATM
Chapter 2
ATM
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Advanced Internet Technologies, SS 2005 2.3
B-ISDN and ATM
The goal of broadband ISDN (1990)
Worldwide consistently build high-performance network
Transmission of data, audio, video
Standardization via ITU (CCITT)
ATM (Asynchronous Transfer Mode) was selected as the base
technology for B-ISDN
ATM is part of the ITU specification of B-ISDN Additional specifications have been published by the ATM Forum
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Advanced Internet Technologies, SS 2005 2.4
Introduction
ATM: Asynchronous Transfer Mode
Based on standardized protocols
Integrated technology for multiple services
Data
Speech / Audio
Video
Usable in LAN and WAN areas
Highly scalable
Support for different connection qualities -> real-time!
Employment of asynchronous time multiplex technologies for flexibility,supporting various transmission bandwidths
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Advanced Internet Technologies, SS 2005 2.5
Properties
Data packets of fixed size, named cells
ATM cells have a length of 53 byte (5 byte header, 48 byte payload)
This allows a high speed processing including massive parallel hardwareoperations
At a payload length of 48 byte, the packetisation delay (time to fill a cellwith 64 Kbit/s digitized voice samples)
Connection oriented
point-to-point
point-to-multipoint Connections may have a fixed (reserved) bandwidth and guaranteed
quality of service characteristics
Centralized coordination of permissions to send (in contrast to tokentechniques or CSMA/CD)
No shared medium Dedicated bandwidth
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Advanced Internet Technologies, SS 2005 2.6
Standardization
ITU-T: International Telecommunications Union – Telecommunications
Standards Section (formerly CCITT)
http://www.itu.ch/
ETSI: European Telecommunications Standards Institute
http://www.etsi.fr/
ANSI: American National Standards Institute
http://web.ansi.org/
ATM-Forum
Development of industry standards allowing a fest development of new
products
http://www.atmforum.com/
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Advanced Internet Technologies, SS 2005 2.7
ATM Layer Model
User plane: information flow between the layers
Control plane: connection setup, maintenance and termination
Management plane: meta-signaling and OAM (Operation and Maintenance)
information flow
AAL Type
ATM Layer
Service Class /
Service Category
(CBR, nrt-VBR,rt-VBR, UBR, ABR)
AAL Service Class
(Class A / B / C / D )
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Advanced Internet Technologies, SS 2005 2.8
Physical Layer
Physical medium sends and receives a bit stream
Bit timing
Transmission convergence
The physical layer adopts the ATM cells received from the ATM layer
to the bit stream required by the physical layer (cell coding)
Direct cell transmission
Cell adaptation to existing transmission frames PLCP (Physical Layer Convergence Protocol) based cell adaptation
HEC (Header Error Correction) generation – an element of the ATM layer
Information flow to the management and to the supervision at thephysical layer (OAM, Operation and Maintenance)
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Advanced Internet Technologies, SS 2005 2.9
Physical Layer II
Transmission speeds
PDH (Plesiochronous Digital Hierarchy)
Europe: 2,048 Mbit/s, 8,448 Mbit/s, 34,368 Mbit/s, 139,264 Mbit/s
USA: 1,544 Mbit/s, 6,312 Mbit/s, 44,736 Mbit/s, 254,176 Mbit/s
SONET (Synchronous Optical NETwork) - USA
SDH (Synchronous Digital Hierarchy) - Europe
OC-3/STM-1: 155,520 Mbit/s
OC-12/STM-4: 622,080 Mbit/s
OC-48/STM-16: 2.48832 Gbit/s
OC-192/STM-64: 9.953280 Gbit/s
OC-768/STM-256: 39.813120 Gbit/s
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Advanced Internet Technologies, SS 2005 2.10
ATM Layer
Transport of ATM cells between the communication end points
Tasks of the user and control plane
Connection setup, multiplexing/de-multiplexing and maintaining ATM
connections
Generation of ATM cell headers (exception: HEC)
Negotiation of QoS (Quality of Service) parameters
Traffic and overload control
OAM cells
cells of the management plane
Meta-signalling
initial signalling to set up signalling VCs (Virtual Channels)
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Advanced Internet Technologies, SS 2005 2.11
ATM Cell Format
53 Byte
5 Byte Header
48 Byte Payload
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Advanced Internet Technologies, SS 2005 2.12
ATM Cell Types
UNI/NNI (User-Network-Interface / Network-Network-Interface) cells:data communication
Transmission of user data
Transmission of signalling data (connection setup, maintenance, tear down)
Idle cells: decoupling of the cell rate at the sender and the available bandwidth of
the transmission medium
Empty cells: contain VPI/VCI (Virtual Path Identifier / Virtual Channel Identifier) but
no payload
OAM cells: contain control and service information
VP/VC (Virtual Path/Virtual Channel) OAM cells: fault management, loopback, and
continuity check (CC) cells; F4: used in VPs, F5: used in VCs
Reserved VCI/VPI values
….
VCI=18, VPI=0PNNI (Private Network-to-Network Interface)
VCI=5Point-to-point signaling
VCI=16, VPI=0ILMI (Interim Local Management Interface)
VCI=1, VPI=0Meta signaling
VPI/VCIFunction
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Advanced Internet Technologies, SS 2005 2.13
ATM Connections
2 Hierarchies: paths and channels
Transmission Path
Virtual Path
V i r t u a l C h a n n e l s
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Advanced Internet Technologies, SS 2005 2.14
Properties of ATM Connections
Start and end at higher layer functions
Have associated service parameters (e.g. cell loss ratio, latency)
Negotiation of transmission parameters by signalling before aconnection is set up (provision of QoS)
Preservation of the transmission order
Unidirectional or bidirectional
Symmetric or asymmetric bandwidth
Permanent
PVC: Permanent Virtual Channel
Dynamic
SVC: Switched Virtual Channel
Signaling: connection setup and tear down
(Two signalling variants specified by ATM Forum: UNI 3.1, UNI 4.0) Routing Protocols (ATM-Forum: P-NNI)
Addressing of end points using E.164 addresses
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Advanced Internet Technologies, SS 2005 2.15
Traffic and Overload Control
Six ATM service categories
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)
Traffic Management 4.0 (ATM Forum)
Connection admission controlVerification if connection setup would be possible
User/network parameter control (UPC/NPC)Supervision of transmission bandwidth by setting a cell loss priority and selectivelydiscarding of cells
Traffic shapingadjustment / smoothing of the transmission rate
Early Packet Discard (EPD)discarding of complete AAL PDUs if single cells are lost
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Advanced Internet Technologies, SS 2005 2.16
Call Admission Control (CAC)
Exchange of information during the connection setup
Source traffic descriptor
Peak cell rate (PCR): upper bound for the maximum cell transmission rate [c/s]
Sustainable cell rate (SCR): upper bound for the average cell transmission
rate [c/s] Maximum burst size (MBS): size of a buffer used for short bursts [c]
Minimum cell rate (MCR): lower bound for the cell transmission rate [c/s]
Cell delay variation tolerance (CDVT)
provides upper bound for the cell jitter
specifies lower bound for the minimum distance between two cells(generated by multiplexing, OAM cells, …)
QoS of the connection (QoS parameters)
Successful completion of the CAC
Traffic agreement is negotiated between the network and the end systems
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Advanced Internet Technologies, SS 2005 2.17
Effects of Network Congestion
Throughput and delay for increasing load
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Advanced Internet Technologies, SS 2005 2.18
Cell Transfer Delay PDF
Probability Density Function (PDF) of Cell Transfer Delay
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Advanced Internet Technologies, SS 2005 2.19
UPC/NPC
Usage Parameter Control / Network Parameter Control
Verification of
Correctness of the VP/VC identifiers in the cell header
Conformance of the cell stream (compliance with the negotiated trafficprofile): the observation whether the measured variable is withinpredefined boundaries.
Actions
Cell passing Cell tagging (warning: CLP bit set to 1)
Cell discarding (in overload situations)
Generic cell rate algorithm (GCRA)
For every cell, a theoretical arrival time (TAT) is calculated based on the
assumption that the distance between all cells is equal
If the actual arrival time corresponds with the TAT (taking a tolerance intoaccount), the cell is conformant (otherwise it is violating the traffic contract)
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Advanced Internet Technologies, SS 2005 2.20
UPC/NPC II
UPC typically at the ingress of an ATM switch
One or two leaky buckets depending on the service category
Processing of cells according to Cell Loss Priority (CLP)
Cells with a CLP bit setting of 1 are discarded before cells with a CLP bitsetting of 0.
Generic cell rate algorithm (GCRA)
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Advanced Internet Technologies, SS 2005 2.21
Traffic Shaping
Different implementation alternatives
leaky bucket / token bucket
virtual scheduling (GCRA)
Reduction of the burst size and removal of the cell delay variation (by
increasing of the delay)
Important note: the order of the cells is not changed
Token Bucket shaper:
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Advanced Internet Technologies, SS 2005 2.22
Early Packet Discard (EPD)
EPD buffer threshold to prevent overload situations
If threshold is exceeded, complete AAL5 PDUs are dropped
→ performance enhancement
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Advanced Internet Technologies, SS 2005 2.23
Quality of Service
Parameter are negotiated at connection setup (ITU I.356/UNI4.0) Cell error ratio
Severely errored blocks
Cell loss ratio*
Cell misinsertion ratio
Cell transfer delay* Mean cell transfer delay
Cell delay variation*
*: currently unused
Different traffic classes (ATM Service Classes) Constant bit-rate (CBR)
Delay sensitive CBR cell stream
Variable bit rate - real time (VBR-rt)
Delay sensitive VBR cell stream
Variable bit rate - non real time (VBR-nrt)
Delay insensitive VBR cell stream
Unspecified bit rate (UBR)
Best effort
Available bit rate (ABR)
Dynamic bandwidth allocation if available
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Advanced Internet Technologies, SS 2005 2.24
Quality of Service II
SpecifiedUnspecifiedUnspecifiedUnspecifiedUnspecified
Flow control
Closed loop
Unspecified
Unspecified
Unspecified
Unspecified
Unspecified
Unspecified
Unspecified
Specified
Specified
Specified
Specified
Specified
Specified
Specified
QoS parameters
Peak-to-peak CDV
maxCTD
CLR
Specified
n/a
Specified
Specified
n/a
n/a
Specified
Specified
n/a
Specified
Specified
n/a
Specified
n/a
n/a
Traffic parameters
PCR and CDVT(pcr)
SCR, MBS, CDVT(scr)MCR
ABRUBRVBR-nrtVBR-rtCBR Attribute
PCR Peak Cell Rate
CDVT Cell Delay Variation ToleranceSCR Sustainable Cell Rate
MBS Maximum Burst Size
MCR Minimum Cell Rate
maxCTD maximum Cell Transfer Delay
CLR Cell Loss Rate
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Advanced Internet Technologies, SS 2005 2.25
ATM Adaptation Layer
AAL (ATM Adaptation Layer): mapping data structures between higher layers and ATM cells
Criteria:
Time constraints
Bit rate (constant, variable) Connection type (connection oriented / connection less)
Convergence Sublayer (CS)
Building CS-PDUs out of an application generated byte stream
Segmentation and Reassembly Sublayer (SAR) Convert CS-PDUs into 48 byte fragments which fit in the payload of ATM cells
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Advanced Internet Technologies, SS 2005 2.26
ATM Adaptation Layer II
Example: AAL 3/4
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ATM Adaptation Layer III
AAL0: “native” ATM
AAL1: constant bit rate (circuit emulation)
AAL2: transmission of data streams with variable bit rates and well defined
time constraints between sender and receiver
AAL3/4: Variable bit rate without any time constraints
AAL5: simplified AAL3/4 (no multiplexing of cells)
SAAL: Signalling AAL,
SSCOP (Service-Specific Connection-oriented Protocol)
and SSCF (Service-Specific Convergence Fuction)over AAL5
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Advanced Internet Technologies, SS 2005 2.28
ATM Adaptation Layer IV
AAL Service Classes and AAL Types
Connectionless
Date Transfer
Bit Rate
Connection
Mode
Examples
of
Services
Circuit
Emulation
Constant BitRate Video
and Audio
Constant Variable
Connection Oriented Connectionless
Variable Bit
Rate Video
and Audio
Connection-
oriented
DataTransfer
AAL
TYPEAAL 1 AAL 2
AAL 3/4
AAL 5
Class A Class B Class C Class D
Related Not Related
AAL ServiceClass
Timingbetween
Source and
Destination
AAL3/4AAL 5
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Advanced Internet Technologies, SS 2005 2.29
Convergence Sublayer
Common part: to add / to remove header and trailer
Unreliable transmission of data packets of variable length
Connection setup between two CPCS (Common Part Convergence
Sublayer) end points
Preservation of the order within a single CPCS connection
Error detection and handling
Handling of overload information
Handling of cell loss priorities
Dropping of incomplete CPCS PDUs
Service specific:
Q.SAAL (SSCS: specification for signaling channels)
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Advanced Internet Technologies, SS 2005 2.30
Segmentation and Reassembly Sublyaer
Identification of the next SAR PDU to transmit
PTI (Payload Type Indication) informs about start and end of a SAR PDU
AAL5: Last cell of an AAL frame: PTI=1
Handling of overload
Handling of cell loss priorities
Check for ordering of SAR PDUs
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Advanced Internet Technologies, SS 2005 2.31
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Advanced Internet Technologies, SS 2005 2.32
AAL 5 Protocol
CPCS-PDU Payload PAD CPI Length
1 2 40 - 47
CPCS
UU
1
CRC-32
AAL5 is a simple and efficient AAL (SEAL) to perform a subset of the functions
of AAL3/4
The CPCS-PDU payload length can be up to 65,535 octets and must use PAD
(0 to 47 octets) to align CPCS-PDU length to a multiple of 48 octets
PAD Padding
CPCS-UU CPCS User-to-User Indicator
CPI Common Part Indicator
Length CPCS-PDU Payload LengthCRC-32 Cyclic Redundancy Chuck
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Advanced Internet Technologies, SS 2005 2.33
Higher layer
Common part
convergence
sublayer
SAR sublayer
ATM layer
PTI = 0
Service specific
convergence
sublayer
Assume null
48
(1)
Information
TPAD
…
…
Information
48
(0)
48
(0)
PTI = 0 PTI = 1
AAL 5 Layering
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Advanced Internet Technologies, SS 2005 2.34
SAAL
SAAL: Adaptation layer for signaling meta signaling
signaling AAL
ITU Q.2100
Offers a reliable service for the higher layer signaling (Q.2931) Q.2931 has no error correction mechanisms
SSCS sublayer: realizes SSCOP protocol (Service SpecificConnection Oriented Protocol)
Sequence continuity Error correction, retransmission
Flow control
Keep alive
Connection control
Exchange of status information between sender and receiver
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Advanced Internet Technologies, SS 2005 2.35
ATM Network Components
ATM Hosts
ATM Switches
ATM Edge Devices
Interconnection of ATM networks and non-ATM networks
ATM Interfaces (public/private) UNI (User Network Interface): defines protocols for the communication between
hosts and switches
NNI (Network to Network Interface): defines the interface between two network
components
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Advanced Internet Technologies, SS 2005 2.36
Higher Layers
Signaling, Routing UNI – User Network Interface
Signalling Interface at ATM end systems
PNNI - Private Network-to-Network Interface
Routing Interface ILMI - Integrated Local Management Interface
Management Interface, using SNMP messages without UDP and IP
Addressing
NSAP (Network Service Access Point) addressing
Three NSAP-like address formats
DCC (Data Country Code) ATM Format
ICD (International Code Designator) ATM Format
E.164 ATM Format.
Procedure E.164 number is filled with leading zeros to make 15 digits.
A F16 is padded to make 8 bytes.
AFI and DSP are added.
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Advanced Internet Technologies, SS 2005 2.37
User Network Interface – Connection Setup
Host A: specification of bandwidth, QoS and destination address
Within the network:
Verification of the available resources
Acceptance / rejection of the request
Reservation of the required resources
Maintenance of the routing tables
Host B: acceptance / rejection of the connection request
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Advanced Internet Technologies, SS 2005 2.38
User Network Interface – Connection Release
Host A: connection release message
Within the network:
Release of resources belonging to the connection
Acknowledgement of the connection release message
Host B: acknowledgement of the connection release message
U N t k I t f III
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Advanced Internet Technologies, SS 2005 2.39
User Network Interface III
ATM point-to-multipoint connections
Extensions in UNI 4.0 Signaling Multicast (leaf initiated join)
Frame discard
Signalling of more QoS parameters (CLR, meanCTD, maxCTD, CDV, ....)
ATM M t d R ti P t l
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Advanced Internet Technologies, SS 2005 2.40
ATM Management and Routing Protocols
Defined by ATM Forum
PNNI (Private Network-to-Network Interface)
a hierarchical, dynamic link-state routing protocol
ILMI (Interim Local Management Interface)
a protocol defined by the ATM Forum for setting and capturing physical layer, ATMlayer, virtual path, and virtual circuit parameters on ATM interfaces.
ILMI uses simple network management protocol (SNMP) messages without User
Datagram Protocol (UDP) and IP
ILMI organizes managed objects into the following four management information
bases (MIBs): Textual Conventions MIB - Defines textual conventions and object IDs
Link Management MIB - Physical layer, ATM layer, Virtual path connection,
Virtual channel connection
Address Registration MIB - address registration mechanism to automatically
configure network prefixes in end-systems.
Service Registry MIB - general-purpose service registry for locating ATM
network services such as a LAN Emulation Configuration Server (LECS) in
LANE.
P i t N t k t N t k I t f P t l
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Advanced Internet Technologies, SS 2005 2.41
Private Network-to-Network Interface Protocol
PNNI: also known as Private Network Node Interface Protocol Setup of SVCs in networks with NSAP (Network Service Access Point)
addressing in a multivendor environment
Hierarchical routing structure, similar to OSPF
Using topology and resource information to setup paths
PNNI Phase 0: Inter-Switch Signaling Protocol (IISP)
Signalling protocol for the communication between ATM switches(administratively configurable address prefixes)
PNNI Phase 1:
QoS support
scalability and reachability
Signaling is based on UNI3.1/4.0 with some extensions
P NNI QoS
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Advanced Internet Technologies, SS 2005 2.42
P-NNI - QoS
CAC (connection admission control) Admission control at each node along the path
Topology state protocol
GCAC (generic CAC) Determination of the shortest path over all nodes which comply with the
ABR and CLR Additionally, the path is verified using the QoS requirements (CDV, …)
Source node creates a “Designated Transit List“ containing the complete
route
Crankback - possibility for a rollback
Crankback:
PNNI Hierarchy
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Advanced Internet Technologies, SS 2005 2.43
PNNI - Hierarchy
Scalability: hierarchical routing protocol
Summary of the reachability information at each hierarchy
Identification using NSAP addresses
Problems:
internetworking with
other networks
Complexity in route
aggregation
ILMI Integrated Local Management Interface
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Advanced Internet Technologies, SS 2005 2.44
ILMI - Integrated Local Management Interface
Protocol for the bidirectional exchange of management information
Monitoring of systems
Management of systems
Using SNMP (simple network management protocol) for the
communication (without UDP/IP)
Fundamentals: data base (ATM-UNI-MIB) with well defined commands
for accessing the data base: AAL encapsulated SNMP messages,
community name ILMI
ILMI Address Registration
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Advanced Internet Technologies, SS 2005 2.45
ILMI - Address Registration
Bidirectional address registration
Dynamic exchange of address information between end systems and
the network at the UNI
The ATM host informs the switch about its ESI address
esiAddress: end system ID portion of the ATM NSAP address in the
format xxxxxxxxxxxx.xx
The ATM switch provides the address prefix to the host
Protocol for automatic address registration
Benefits:
There is no need to configure the prefix at each host
There is no need for an additional address resolution protocol in the
switches (all hosts register first)
Applications
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Applications
Multimedia Video over ATM
Benefits:
guaranteed QoS parameters
Low latency Resource sharing between multiple applications
Drawbacks:
Complexity in the maintenance of ATM networks
Examples:
M-JPEG codecs: 15Mbit/s, TV quality
MPEG2 codecs: 3-40Mbit/s, DVD up to studio quality
Lossless SDI: 270Mbit/s, uncompressed studio signals
IP/LAN over ATM CLIP (Classical IP over ATM / Classical IP)
MPOA (Multi-Protocol over ATM)
LANE (LAN Emulation)
Multiprotocol Encapsulation over AAL5 (RFC2684)
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Advanced Internet Technologies, SS 2005 2.47
Multiprotocol Encapsulation over AAL5 (RFC2684)
RFC2684
LLC/SNAP encapsulation
LLC data packets are encapsulated into AAL5 CPCS PDUs
Transmission of a complete data stream in a single VC A special header informs about the encapsulated protocol
All protocols based on Ethernet, FDDI, … can be transported
VC based multiplexing
Communication end point in layer 3
Avoiding special LLC headers by using separate VCs for each
protocol
More efficient than LLC encapsulation
Classical IP
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Advanced Internet Technologies, SS 2005 2.48
Classical IP
Specification of a complete IP implementation for ATM Allows unicast communication only
Very efficient Support for large MTU sizes
Direct encapsulation of IP packets into AAL PDUs
LIS: logical IP subnet ATMARP/InATMARP: protocol similar to ARP to resolve IP to ATM addresses
InATMARP functions are provided by an ATMARP server
There must be an ATMARP server in each LIS
Classical IP II
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Classical IP II
Each ARP client must register its IP/ATM address information at the ATMARP server or request an IP address from the ATMARP server
LANE
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Advanced Internet Technologies, SS 2005 2.50
LAN Emulation: connecting LANs over ATM networks
The properties of ATM are completely hidden
Complete emulation of the LAN MAC layer
Thus, no need to modify existing LAN software
But, no special ATM features can be used, e.g. QoS
Provisioning of a special broadcast mechanism, which is also used for
multicast
Translation of MAC to ATM addresses
Transmission of LAN packets using AAL5 PDUs
Modules:
LANE client (LEC)
LANE server (LES)
LANE configuration server (LECS)
Broadcast and unknown server (BUS)
LANE II
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Advanced Internet Technologies, SS 2005 2.51
LEC (LANE client) Control functions
Data exchange using the ATM interface
Interface to the application as a standard LAN MAC interface
LES (LANE server) Control and maintenance of an E-LAN (emulated LAN)
Registration of LECs
Mapping of MAC to ATM addresses
BUS (broadcast and unknown server)
Delivery of broadcast, multicast and unknown packets received from anyLANE client
All packets with a broadcast or multicast address
Packets which cannot be delivered directly, e.g. because thecorresponding ATM address cannot be resolved
Sequential processing of the single messages (AAL5 does not allow thechange of the order of PDUs)
LANE III
7/29/2019 ATM Overview Shorthand
http://slidepdf.com/reader/full/atm-overview-shorthand 52/53
Advanced Internet Technologies, SS 2005 2.52
LECS (LANE configuration server) Management of the different emulated LANs and the associated LANE
servers
Configuration database allowing a LANE client to find the appropriate
LANE server for a specific emulated LAN LECS address
Statically configured in LES and LEC
Well known address
via ILMI
LANE IV
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