Ccn unit1 for 7th SEM EC by Prof. suresha V

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UNIT-1

Network Models

Suresha V. Professor, Dept. of E&C, KVG College Of Engineering. Sullia, D.K - 574 327

3Suresha V. Professor, Dept. of E&C, KVG College Of Engineering. Sullia, D.K - 574 327

INRODUCTION: A network is a combination of hardware and software that sends data from

one

location to another.

The hardware consists of the physical equipment that carries signals from one

point of the network to another.

The software consists of instruction sets that make possible the services that

we expect from a network.

Computer networks are very complex object, hence it is partitioned in to

vertical set of levels. each level called layer.


1.1. LAYERED TASKS:LAYERED TASKS:

We use the concept of layers in our daily life. As an example, let us consider two friends who We use the concept of layers in our daily life. As an example, let us consider two friends who

communicate through postal mail. The process of sending a letter to a friend would be complex communicate through postal mail. The process of sending a letter to a friend would be complex

if there were no services available from the post office.if there were no services available from the post office.

Figure shows the tasks involved in sending a letter


1.1. LAYERED TASKS:LAYERED TASKS:

Sender, Receiver and Carrier:

Hierarchy:

• Higher Layer • Middle Layer • Lower Layer

Services:

• The Each layer uses the services of the layer immediately below it.


2. THE OSI MODEL ***2. THE OSI MODEL ***

• Open Systems Interconnection model.

• It is a 7 layers model

• It was first introduced in the late 1970s

• OSI developed by International Standards Organization (ISO).

• It is a multinational body dedicated to worldwide agreement

on international standards.


The purpose of the OSI model:• To show how to facilitate communication between different systems

without requiring changes to the logic of the underlying hardware and

software.

• The OSI model is not a protocol; it is a model for understanding and

designing a network architecture that is flexible, robust, and

interoperable.

• The OSI model is a layered framework for the design of network systems

that allows communication between all types of computer systems.

ISO is the organization. OSI is the model.


2.1 Layered Architecture ***2.1 Layered Architecture ***

Fig: 2.1 Seven layers of the OSI model


2.1 Layered Architecture (cont’d….)2.1 Layered Architecture (cont’d….)

The OSI model is composed of seven layers:

• Physical (layer1), Data link (layer2), Network (layer3)

• Transport (layer4), Session (layer5), Presentation (layer6)

• Application (layer7)

Layer:

• Designer identified which networking functions had related uses and

collected those functions into discrete groups that became the layers.

• The OSI model allows complete interoperability between otherwise

incompatible systems.

• The Each layer uses the services of the layer immediately below it.


Peer-to-peer Processes:Peer-to-peer Processes:

Figure 2.2 The interaction between layers in the OSI model


Peer-to-peer Processes Peer-to-peer Processes (cont’d)(cont’d) ::

• Layer x on one machine communicates with layer x on another machine - called Peer to-Peer Processes.

Interfaces between Layers:

• Each interface defines what information and services a layer must provide for the layer above it.

• Well defined interfaces and layer functions provide modularity to a network

Organizations of the layers:

• Network support layers : Physical (layer1), Data link (layer2), Network (layer3)

• User support layers : Session (layer5), Presentation (layer6),Application (layer7) • Transport layer (Layer 4) : links the two above subgroups

• It allows interoperability among unrelated software systems


Peer-to-peer Processes Peer-to-peer Processes (cont’d)(cont’d) ::

• The data portion of a packet at level N-1 carries the whole packet from level N. – The concept is called encapsulation.

Figure 2.4 An exchange using the OSI model


3. LAYERS IN THE OSI MODEL:3. LAYERS IN THE OSI MODEL:

• In this section we briefly describe the functions of each layer in the OSI model.In this section we briefly describe the functions of each layer in the OSI model.

Topics to be discussed in this section:Topics to be discussed in this section:

• Physical Layer

• Data Link Layer

• Network Layer

• Transport Layer

• Session Layer

• Presentation Layer

• Application Layer


3.1 Physical Layer3.1 Physical Layer ::

Physical layer coordinates the functions required to transmit a bit stream over

a physical medium.

The physical layer is responsible for movements of individual bits from one

hop (node) to the next.

It deals with the mechanical and electrical specification of the primary connections:

cable, connector

Bits


3.1 Physical Layer3.1 Physical Layer (cont…..)

Physical layer is concerned with the following:

• Physical characteristics of interfaces and medium: Types of medium and interfaces

• Representation of bits: 1’s or 0’s Encoded in to Electrical or optical

• Data rate : transmission rate: speed in bps

• Synchronization of bits: Both Tx and Rx are in the same clock

• Line configuration : pt. to pt. or Multipoint transmission

• Physical topology: Way in which the n/w formed, ring bus, etc..

• Transmission mode: simplex, half or full duplex


3.2 Data Link Layer3.2 Data Link Layer

The data link layer is responsible for moving frames from one hop (node) to the next.

Major duties of Data Link Layer:Data Link Layer:• Framing• Physical addressing• Flow control• Error control• Access control


3.2 Data Link Layer(con’t..):3.2 Data Link Layer(con’t..):

• Hop-to-hop (node-to-node) delivery


3.3 Network Layer3.3 Network Layer

The network layer is responsible for the delivery of individual packets from the source

host to the destination host.

Other responsibilities of network layer includes

• Logical addressing

• Routing


3.3 Network Layer(con’t…)3.3 Network Layer(con’t…)

• Fig 3.3 illustrates end-to-end delivery by the network layerFig 3.3 illustrates end-to-end delivery by the network layer

Figure 3.3: Source-to-destination deliveryFigure 3.3: Source-to-destination delivery


3.4 Transport Layer3.4 Transport Layer

The transport layer is responsible for the delivery of a message from one process to another.


3.4 Transport Layer(con’t…)3.4 Transport Layer(con’t…)

Other responsibilities of the transport layer includes the following:

(1) Service-point addressing.(2) Segmentation and reassembly.

(3) Connection control. (4) Flow control. (5) Error control.


3.5 Session Layer3.5 Session Layer

The session layer is responsible for dialog control and synchronization.

Specific responsibilities of the session layer

• Dialog control.

• Synchronization.


3.6 Presentation Layer3.6 Presentation Layer

The presentation layer is responsible for translation, compression, and encryption

Specific responsibilities of the presentation layer are

Translation

Encryption

Compression


3.7 Application Layer3.7 Application Layer

The application layer is responsible for providing services to the user.

The major duties of the application

Network virtual terminal

File transfer, access, and management

Mail services

Directory services


o Summary of LayersSummary of Layers


4.TCP / IP PROTOCOL SUITE (4.TCP / IP PROTOCOL SUITE (Transmission Control Protocol / Internet Protocol)Transmission Control Protocol / Internet Protocol)

• TCP/IP is a hierarchical protocol made up of interactive modules, each of which provides a specific functionality.• The layers of the TCP/IP protocol suite contain relatively independent protocols that can be mixed and matched depending on the needs of the system. • The term hierarchical means that each upper-level protocol is supported by one or more lower-level protocols.

The original TCP/IP protocol suite was defined as having four layers.The original TCP/IP protocol suite was defined as having four layers.

Host-to-networkHost-to-network

Internet.Internet.

Transport.Transport.

Application. Application.

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4.TCP / IP PROTOCOL SUITE (4.TCP / IP PROTOCOL SUITE (Transmission Control Protocol / Transmission Control Protocol / Internet Protocol)Internet Protocol) Figure :TCP/IP and OSI model


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4.TCP / IP PROTOCOL layers description 4.TCP / IP PROTOCOL layers description

1.1. Physical and Data Link Layers(Host-to-network)Physical and Data Link Layers(Host-to-network)

At the physical and data link layers, TCP/IP does not define any specific protocol.

It supports all the standard and proprietary protocols.

A network in a TCP/IP internetwork can be a local-area network or a wide-area network.

2. Network Layer (IP layer)2. Network Layer (IP layer) TCP/IP supports the Internetworking Protocol.

IP uses four supporting protocols : ARP, RARP, ICMP, and IGMP.

IP (Internetworking Protocol)

ARP (Address Resolution Protocol)

RARP (Reverse Address Resolution Protocol)

ICMP (Internet Control Message Protocol)

IGMP (Internet Group Message Protocol) Suresha V. Professor, Dept. of E&C, KVG College Of Engineering. Sullia, D.K - 574 327


4.TCP / IP PROTOCOL layers description(con’t…)4.TCP / IP PROTOCOL layers description(con’t…)

3. 3. Transport LayerTransport Layer

The transport layer was represented in TCP/IP by two protocols : TCP and UDP.

IP is a host-to-host protocol

TCP and UDP are transport level protocols responsible for delivery

of a message from a process to another process.

UDP (User Datagram Protocol)

TCP (Transmission Control Protocol)

SCTP (Stream Control Transmission Protocol)


4.TCP / IP PROTOCOL layers description(con’t…)4.TCP / IP PROTOCOL layers description(con’t…)

4. Application Layer4. Application Layer

The application layer in TCP/IP is equivalent to the combined session,

presentation, and application layers in the OSI model.

Many protocols are defined at this layer they are as follows:

SMTP,FTP,HTTP,DNS,SNMP,TELNET….


5. ADDRESSING ****5. ADDRESSING ****

Four levels of addresses are used in an internet employing the TCP/IP protocols: Four levels of addresses are used in an internet employing the TCP/IP protocols:

physical, logical, port, and specific.physical, logical, port, and specific.

Figure 2.17 figure 5.1 Addresses in TCP/IP


5.ADDRESSING5.ADDRESSING

11. Physical Addresses. Physical Addresses

The physical address, also known as the link address, is the address of a node as defined by its LAN or WAN.

It is included in the frame used by the data link layer.

• The physical addresses have authority over the network (LAN or WAN).

• The size and format of these addresses vary depending on the network.


5. ADDRESSING5. ADDRESSING

1. Physical Addresses (cont..)1. Physical Addresses (cont..)

Example 2.1

In below Figure a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver.

Figure 1. Physical addresses


1. 1. Physical Addresses (cont…)Physical Addresses (cont…)

Example 2.2

Most local-area networks use a 48-bit (6-byte) physical address written as 12

hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon,

as shown below:

07:01:02:01:2C:4B

A 6-byte (12 hexadecimal digits) physical address.


2. 2. Logical AddressesLogical Addresses

Logical addresses are necessary for universal communications that are independent of underlying physical networks.

Physical addresses are not adequate in an internetwork environment where different networks can have different address formats.

A universal addressing system is needed in which host can be identified uniquely, regardless of the underlying physical network.

Example 3

Figure 3 shows a part of an internet with two routers connecting three LANs. Each device

(computer or router) has a pair of addresses (logical and physical) for each connection. In this

case, each computer is connected to only one link and therefore has only one pair of addresses.

Each router, however, is connected to three networks (only two are shown in the figure). So each

router has three pairs of addresses, one for each connection.


2. 2. Logical Addresses( cont..)Logical Addresses( cont..)

Example 3

The physical addresses will change from hop to hop, but the logical addresses usually remain the same.


3. 3. Port AddressesPort Addresses

The IP and the physical address are necessary for a quantity of data to travel from a source to the destination host.

The end object of Internet communication is a process communicating with another process.

For these processes to receive data simultaneously, we need a method to label assigned to a process is called a port address.

A port address in TCP/IP is 16 bits in length.

Example 4

Figure 4. shows two computers communicating via the Internet. The sending computer is running three processes at this time with port addresses a, b, and c. The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination.


33. . Port Addresses (cont’d…)Port Addresses (cont’d…)

Figure 4. Port addresses

The physical addresses will change from hop to hop, but the logical and port addresses usually remain the same.


33. . Port Addresses (cont’d…)Port Addresses (cont’d…)

Example.5

A port address is a 16-bit address represented by one decimal number as shown

4. Specific Addresses4. Specific Addresses

Some applications have user-friendly addresses that are designed for that specific address.

E-mail address

URL (Universal Resource Locator)

753 A 16-bit port address represented as one single number.

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UNIT-1

Using Telephone and Cable Networks for Data Transmission


41 Suresha V. Professor, Dept. of E&C, KVG College Of Engineering. Sullia, D.K - 574 327

1.TELEPHONE NETWORK1.TELEPHONE NETWORK

IntroductionIntroduction

• Beginnings in the late 1800s.Beginnings in the late 1800s.

• Originally an analog system using analog signals to transmit voice.Originally an analog system using analog signals to transmit voice.

• The entire network, which is referred to as the The entire network, which is referred to as the plain old telephone system plain old telephone system (POTS)(POTS)

• Telephone networks use circuit switching.Telephone networks use circuit switching.

Figure 1. A telephone system

Endoffices

Local loop

Trunk

Tandemoffices Regional offices

Trunk

• • •


1.TELEPHONE NETWORK (contd..)1.TELEPHONE NETWORK (contd..)

Major Components of telephone system:

Local Loops: 1). A twisted-pair cable that connects the subscriber telephone to the

nearest end office or local central office

2) . Its B.W is 4000hz for voice communication.

3) . The first three digits of a local telephone number define the office, and

the next four digits define the local loop number

Trunks : 1) Trunks are transmission media that handle the communication between

offices.

2) A trunk normally handles hundreds or thousands of connections through

multiplexing.

3) Transmission is usually through optical fibers or satellite links.


Major Components of telephone system( cont…):

Switching Offices : 1). To avoid having a permanent physical link between any two

subscribers, the telephone company has switches located in a

switching office.

2). Switch connects several local loops or trunks and allows a

connection between different subscribers.


Local-Access Transport Areas (LATAs)

A LATA can be a small or large metropolitan area.

A small state may have one single LATA; a large state may have several

LATAs.

A LATA boundary may overlap the boundary of a state; part of a LATA

can

be in one state, part in another state.

Two types of LATAs Services

1. Intra-LATA Services

2. Inter-LATA Services


Types of LATAs Services (cont…)

1. Intra-LATA Services:

The services offered by the common carriers (telephone companies) inside a LATA

are called intra-LATA services.

The carrier that handles these services is called a local exchange carrier (LEC).

Before the Telecommunications Act of 1996 intra-LATA services were granted to

one single carrier. This was a monopoly.

After 1996,more than one carrier could provide services inside a LATA. The carrier

that provided services

The carrier that provided services before 1996 owns the cabling system (local loops)

and is called the Incumbent Local Exchange Carrier (ILEC).


Intra-LATA Services (cont’d…):

The new carriers that can provide services are called Competitive Local

Exchange Carriers (CLECs).

CLECs would provide other services such as mobile telephone service, toll

calls inside a LATA, and so on.

Figure below shows a LATA and switching offices.


2. Inter-LATA Services

The services between LATAs called Inter-LATA Services

These services handled by Interexchange Carriers (IXCs).

IXCs sometimes called long-distance companies, provide communication services

between two customers in different LATAs.

Major companies providing inter-LATA services include AT&T,MCI, WorldCom,

Sprint, Verizon etc..

The IXCs are long-distance carriers that provide general data communications

services including telephone service.

A telephone call going through an IXC is normally digitized, with the carriers using

several types of networks to provide service.


Points Of Presence (POP) Point of presence (POP) connect several LECs and IXCs.

Each IXC that wants to provide interLATA services in a LATA must have a POP in that

LATA.

The LECs that provide services inside the LATA must provide connections so that every

subscriber can have access to all POPs.

Figure : Point of presences (POPs)


3.Signaling The use of signals for controlling communications.

The sending of a signal from the transmitting end of a telecommunication circuit to

inform a user at the receiving end that a message is to be sent.

The information exchange concerning the establishment and control of a

telecommunication circuit and the management of the network, in contrast to user

information transfer

The signaling system was required to perform other tasks such as

• Providing dial tone, ring tone, and busy tone

• Transferring telephone numbers between offices

• Maintaining and monitoring the call

• Keeping billing information

• Maintaining and monitoring the status of the telephone network equipment

• Providing other functions such as caller ID, voice mail, and so on


• Two types of signaling are used

in-band signaling

out-of-band signaling

NOTE : In modern telephone networks the tasks of data transfer and signaling are separated :

data transfer is done by one network, signaling by another.

Figure : Data transfer and signaling networks


Signaling System Seven (SS7) *** SS7 is a global standard for telecommunications defined by the ITU.

The protocol that is used in the signaling network is called Signaling System Seven (SS7).

The standard defines the procedures and protocol by which network elements in PSTN

exchange information over a digital signaling network to effect wireless (cellular) and

wireline call setup, routing and control.

The SS7 network and protocol are used for:

• Basic call setup, management and tear down.

• Wireless services such as personal communications services (PCS), wireless roaming,

and mobile subscriber authentication.

• Local Number Portability (LNP).

• Toll-free (800/888) and toll (900) wireline services.

• Enhanced call features such as call forwarding, calling party name/number display,

and three-way calling.

• Efficient and secure worldwide telecommunications.


Signaling System Seven (SS7) cont…*** It is very similar to the five-layer Internet model, but the layers have different names

as shown below

Figure : Layers in SS7


Signaling System Seven (SS7) cont’d..

MTP Level 1: The physical layer in SS7 called message transport part (MTP) level I uses several

physical layer specifications such as T-l (1.544 Mbps) and Digital Carrier (64 kbps).

MTP Level 2 : The MTP level 2 layer provides typical data link layer services such as packetizing,

using source and destination address in the packet header, and CRC for error

checking.

MTP Level 3: The MTP level 3 layer provides end-to-end connectivity by using the datagram

approach to switching. Routers and switches route the signal packets from the

source to the destination.

Transport Layer : The signaling connection control point (SCCP) is used for special services such

as 800-call processing.


Signaling System Seven (SS7) cont’d..

Upper Layers: There are three protocols at the upper layers.

1). TUP : Telephone user port (TUP) is responsible for setting up voice calls.

It receives the dialed digits and routes the calls.

2). TCAP : Transaction capabilities application port (TCAP) provides remote calls that let an

application program on a computer invoke a procedure on another computer.

Its primary purpose is to facilitate multiple concurrent dialogs between the same

sub- systems on the same machines, using Transaction IDs to differentiate these.

3). ISUP : ISDN user port (ISUP) can replace TUP to provide services similar to those of an

ISDN network.


Services Provided by Telephone Networks ***

Telephone companies provide two types of services: Analog and Digital.

Analog Services:

1. Analog Switched Services

2. 800 service

3. wide-area telephone service (WATS).

4. 900 services

5. Analog Leased Service

Digital Services:

1. switched/56 service .

2. digital data service(DDS).


4. DIAL- UP MODEMS

Traditional telephone lines can carry frequencies between 300 and 3300 Hz of BW 3000 Hz.

This range is used for transmitting voice

The effective bandwidth of a telephone line being used for data transmission is 2400 Hz,

covering the range from 600 to 3000 Hz.

Figure : Telephone line bandwidth


MODEM is a the device: a signal modulator and a signal demodulator.

A modulator creates a bandpass analog signal from binary data. A demodulator recovers

the binary data from the modulated signal.

.

Figure: Modulation/demodulation

4. DIAL- UP MODEMS(cont..)


Modem Standards ** Most popular modems available are based on the V-series standards published by the ITU-T

V.32 modem:

It uses a combined modulation and encoding technique called trelliscoded modulation.

The V.32 calls for 32-QAM with a baud rate of 2400.

Because only 4 bits of each symbol represent data, the resulting data total data rate is 4 x 2400 =

9600 bps.

V.32bis Modem:

It was the first of the ITU-T standards to support 14,400-bps transmission.

The V.32bis uses 128-QAM transmission (7 bits/baud with I bit for error control) at a rate of 2400

baud (2400 x 6 = 14,400 bps).


Modem Standards (cont’d…) V.34bis Modem

The V.34bis modem provides a bit rate of 28,800 with a 960-point constellation

Bit rate of 33,600 bps with a 1664-point constellation

V.90 Modem

V.90 modems with a bit rate of 56,000 bps. Also called 56K modems.

These modems may be used only if one party is using digital signaling (such as through ISP).

They are asymmetric in that the downloading rate is a maximum of 56 kbps, while the uploading

rate

can be a maximum of 33.6 kbps.

V.92 Modem

The standard above V90 is called V.92.

These modems can adjust their speed, and if the noise allows, they can upload data at the rate of

48 kbps. The downloading rate is still 56 kbps.

The modem has additional features. For example, the modem can interrupt the Internet connection

when there is an incoming call if the line has call-waiting service.


Modem Standards (cont’d…) Why downloading data rate is high and uploading rate low?

Fig: Uploading and downloading in 56K modems


5.DIGITAL SUBSCRIBER LINE (DSL) ***

Digital subscriber line (DSL) technology is one of the most promising for Digital subscriber line (DSL) technology is one of the most promising for

supporting high- speed digital communication supporting high- speed digital communication over the existing over the existing local loopslocal loops..

After traditional modems reached their After traditional modems reached their peak data ratepeak data rate, telephone companies, telephone companies

developed another technology, DSL, to provide developed another technology, DSL, to provide higher-speed access higher-speed access to the to the

Internet. Internet.

DSL technology is a set of technologies,i.e

o Asymmetric Digital Subscriber Line (ADSL)

o Very High-bit-rate Digital Subscriber Line (VDSL)

o High-bit-rate Digital Subscriber Line (HDSL)

o Symmetric Digital Subscriber Line (SDSL).

NOTE: The set is often referred to as xDSL, where x can be replaced by A, V, H, or S.


5.DIGITAL SUBSCRIBER LINE (DSL) cont..

ADSL ( Asymmetric Digital Subscriber Line)

ADSL, like a 56K modem, provides higher speed in the downstream direction than in

the upstream direction. That is the reason it is called ‘asymmetric’.

Unlike the asymmetry in 56K modems, the designers of ADSL specifically divided the

available bandwidth of the local loop unevenly for the residential customer.

The service is not suitable for business customers who need a large bandwidth in both

directions.

But how does ADSL reach a data rate that was never achieved with traditional

modems?

• The existing local loops can handle bandwidths up to 1.1 MHz. the entire 1.1 MHz

is available for data and voice communications. ADSL is an adaptive technology. The system uses a data rate based on the condition of the local loop line.

NOTE: ADSL is an asymmetric communication technology designed for residential users, it is

not suitable for businesses.


ADSL (cont’d…) Discrete Multitone Technique (DMT)

The modulation technique that has become standard for ADSL is called the Discrete Multitone Technique (DMT) which combines QAM and FDM.

Figure 10 : Discrete multitone technique


Discrete Multitone Technique (cont’d…)

There is no set way that the bandwidth of a system is divided. Each system can decide

on its bandwidth division. Figure 11: Bandwidth division in ADSL

Typically, an available bandwidth of 1.104 MHz is divided into 256 channels.

Each channel uses a bandwidth of 4.312 kHz

The figure 10 & 11 shows how bandwidth can be divided into the following:

Voice: Channel 0 is reserved for voice communication.

Idle: Channels 1 to 5 are not used and provide a gap between voice and data communication.


Upstream data and control

• Channels 6 to 30 (25 channels) are used for upstream data transfer (24 channels)

and control (One channel).

• If there are 24 channels, each using 4 kHz (out of 4.312 kHz available) with QAM

modulation.

• we have 24 x 4000 x 15, or a 1.44-Mbps bandwidth, in the upstream direction.

• However, the data rate is normally below 500 kbps because some of the carriers

are deleted at frequencies where the noise level is large.

Downstream data and control

• Channels 31 to 255 (225 channels) are used for downstream data transfer and

control.

• One channel is for control, and 224 channels are for data.

• If there are 224 channels, we can achieve up to 224 x 4000 x 15, or13.4 Mbps.

• However, the data rate is normally below 8 Mbps, because some of the carriers

are deleted at frequencies where the noise level is large.


ADSL Implementation

Customer Site: ADSL Modem (down link)

Figure : ADSL modem

ADSL modem installed at a customer's site. The local loop connects to a splitter which

separates voice and data communications.

The ADSL modem modulates and demodulates the data, using DMT, and creates

downstream and upstream channels


ADSL Loop Architecture(not in the syllabus)

Subscriber premisesCentral Office

ISP

Voice Switch

DSL


ADSL (cont’d…)

Telephone Company Site: DSLAM (uplink) At the telephone company site, Instead of an ADSL modem, a device called a digital

subscriber line access multiplexer (DSLAM) is installed, it packetizes the data to be sent

to the Internet (ISP server).

Figure : DSLAM


ADSL Lite The installation of splitters at the border of the premises and the new wiring for the data

line can be expensive and impractical enough to dissuade most subscribers.

A new version of ADSL technology called ADSL Lite (or Universal ADSL or splitterless ADSL) is

available for these subscribers.

This technology allows an ASDL Lite modem to be plugged directly into a telephone jack

and connected to the computer.

The splitting is done at the telephone company.

ADSL Lite uses 256 DMT carriers with 8-bit modulation

It can provide a maximum downstream data rate of 1.5 Mbps and an upstream data rate of

512 kbps.


HDSL The high-bit-rate digital subscriber line (HDSL) was designed as an alternative to the T-1 line (1.544 Mbps). The T-1line uses alternate mark inversion (AMI) encoding, which is very susceptible to attenuation at high frequencies. This limits the length of a T-l line to 3200 ft (1 km). For longer distances, a repeater is necessary, which means increased costs. HDSL uses 2B1Q encoding which is less susceptible to attenuation. A data rate of 1.544 Mbps (sometimes up to 2 Mbps) can be achieved without repeaters up to a distance of 12,000 ft (3.86 km). HDSL uses two twisted pairs (one pair for each direction) to achieve full-duplex transmission.

SDSL The symmetric digital subscriber line (SDSL) is a one twisted-pair version of HDSL. It provides full-duplex symmetric communication supporting up to 768 kbps in each direction. SDSL, which provides symmetric communication, can be considered an alternative to ADSL. Although this feature meets the needs of most residential subscribers, it is not suitable for residential subscribers that send and receive data in large volumes in both directions.


VDSL The very high-bit-rate digital subscriber line (VDSL), an alternative approach that is

similar to ADSL, uses coaxial, fiber-optic, or twisted-pair cable for short distances.

The modulating technique is DMT.

It provides a range of bit rates (25 to 55 Mbps) for upstream communication at

distances of 3000 to 10,000 ft. The downstream rate is normally 3.2 Mbps.

Table below shows a summary of DSL technologies.

Note: Two-binary, one-quaternary (2B1Q)


5. CABLE TV NETWORKS5. CABLE TV NETWORKS The The cable TV networkcable TV network started as a video service provider, but it has moved to the started as a video service provider, but it has moved to the

business of Internet accessbusiness of Internet access. .

Topics to be discussed in this section :Topics to be discussed in this section :

Traditional Cable Networks

Hybride Fiber-Coaxial (HFC) Network


5. CABLE TV NETWORKS5. CABLE TV NETWORKS

Traditional Cable Networks was called community antenna TV (CATV)

Figure : Traditional cable TV network

NOTE: Communication in the traditional cable TV network is unidirectional.


5. CABLE TV NETWORKS5. CABLE TV NETWORKS (Contd..)

Hybride Fiber-Coaxial (HFC) Network

NOTE: Communication in an HFC cable TV network can be bidirectional


5. CABLE TV NETWORKS5. CABLE TV NETWORKS (Contd..)

CABLE TV FOR DATA TRANSFER

Cable companies are now competing with telephone companies for the residential Cable companies are now competing with telephone companies for the residential

Customer who wants high-speed data transfer. In this section, we briefly discuss this Customer who wants high-speed data transfer. In this section, we briefly discuss this

technologytechnology

1. Bandwidth

2. Sharing.

3. CM and CMTS

4. Data Transmission Schèmes: Data Over Cable System Interface Specification

(DOCSIS).


CABLE TV FOR DATA TRANSFER

(1) Bandwidth:

In an HFC system, the last part of the network, from the fiber node to the subscriber premises, is still a coaxial cable.

This coaxial cable has a bandwidth that ranges from 5 to750 MHz(approx)

To provide Internet access, the cable company has divided this bandwidth into three bands: (1). Video (2) .Downstream data (3).Upstream data bands.

Figure : Division of coaxial cable band by CATV


CABLE TV FOR DATA TRANSFER(cont’d…)

Downstream Video Band:

It occupies frequencies from 54 to 550 MHz.

Since each TV channel occupies 6 MHz, this can accommodate more than

80

channels.

Downstream Data Band

It occupies the upper band, from 550 to 750 MHz.

This band is also divided into 6-MHz channels.

Modulation Downstream data band uses the 64-QAM (or possibly 256-

QAM) modulation technique.

The theoretical downstream data rate is 30 Mbps.



Upstream Data Band:

It occupies the lower band, from 5 to 42 MHz.

This band is also divided into 6-MHz channels.

The upstream data band uses lower frequencies that are more susceptible

to noise and interference. For this reason, the QAM technique is not

suitable for this band. A better solution is QPSK.

Upstream data are modulated using the QPSK modulation technique.

Data Rate There are 2 bits baud in QPSK. The standard specifies 1 Hz/baud;

theoretically, upstream data can be sent at 12 Mbps (2 bits/Hz x 6 MHz).

However, practically the data rate is usually less than 12 Mbps.

The theoretical upstream data rate is 12 Mbps.



(2) Sharing Both upstream and downstream bands are shared by the subscribers.

Upstream Sharing

The upstream data bandwidth is 37 MHz. This means that there are only six 6-MHz

channels available in the upstream direction.

A subscriber needs to use one channel to send data in the upstream direction.

The question is, "How can six channels be shared in an area with 1000,2000, or even

100,000 subscribers?" The solution is timesharing.

Downstream Sharing

The downstream band has 33 channels of 6 MHz. A cable provider probably has

more than 33 subscribers; therefore, each channel must be shared between a

group of subscribers



(3) CM and CMTS To use a cable network for data transmission, need two key devices:

Cable Modem(CM)

Cable Modem Transmission System (CMTS).

1.The cable modem (CM): It is installed on the subscriber premises.

It is similar to an ADSL modem.

Fig: Cable modem(CM)



2. Cable Modem Transmission System(CMTS) The cable modem transmission system (CMTS) is installed inside the distribution hub by the

cable company.

It receives data from the Internet and passes them to the combiner, which sends them to the

subscriber.

The CMTS also receives data from the subscriber and passes them to the Internet.

Figure below shows the location of the CMTS.



4. Data Transmission Schemes: DOCSIS

Multimedia Cable Network Systems (MCNS) designed to create a standard for data

transmission over an HFC network called “Data Over Cable System Interface

Specification “(DOCSIS).

DOCSIS defines all the protocols necessary to transport data from a CMTS to a CM.

Upstream Communication

The following is a very simplified version of the protocol defined by DOCSIS

for upstream communication. It describes the steps that must be followed

by a CM: The CM checks the downstream channels for a specific packet periodically

sent by the CMTS. The packet asks any new CM to announce itself on a

specific upstream channel.

The CMTS sends a packet to the CM, defining its allocated downstream and

upstream channels.


Data Transmission Schemes: DOCSIS (cont..)

Upstream Communication (cont..)

3. The CM then starts a process, called ranging, which determines the distance between the CM and

CMTS. This process is required for synchronization between all CMs and CMTSs for the minislots

used for timesharing of the upstream channels.

4. The CM sends a packet to the ISP, asking for the Internet address.

5. The CM and CMTS then exchange some packets to establish security parameters, which are needed

for a public network such as cable TV.

6. The CM sends its unique identifier to the CMTS.

7. Upstream communication can start in the allocated upstream channel; the CM can contend for the

minislots to send data.

Downstream Communication

1. In the downstream direction, the communication is much simpler. There is no

contention because there is only one sender.

2.The CMTS sends the packet with the address of the receiving CM, using the allocated

downstream channel.


The International Standards Organization created a model

called the Open Systems

Interconnection, which allows diverse systems to

communicate.

The seven-layer OSI model provides guidelines for the development of universally compatible networking protocols.

The physical, data link, and network layers are the network support layers.

The session, presentation, and application layers are the user support layers.

The transport layer links the network support layers and the user support layers.

The physical layer coordinates the functions required to transmit a bit stream over a physical medium.

The data link layer is responsible for delivering data units from one station to the next without errors.

The network layer is responsible for the source-to-destination delivery of a packet across multiple network links.

SUMMARY OF UNIT ONE: NETWORK

MODELS

SUMMARY OF UNIT ONE : NETWORK

MODELS (1/6)


The transport layer is responsible for the process-to-process

delivery of the entire

message.

The session layer establishes, maintains, and synchronizes the interactions between communicating devices.

The presentation layer ensures interoperability between communicating devices through transformation of data into a mutually agreed upon format.

The application layer enables the users to access the network. TCP/IP is a five-layer hierarchical protocol suite developed before the OSI model. The TCP/IP application layer is equivalent to the combined session, presentation, and application layers of the OSI model. Four levels of addresses are used in an internet following the TCP/IP protocols: physical (link) addresses, logical (IP) addresses, port addresses, and specific addresses.


MODELS


MODELS (2/6)


The physical address, also known as the link address, is the

address of a node as defined by its LAN or WAN.

The IP address uniquely defines a host on the Internet.

The port address identifies a process on a host.

specific address is a user-friendly address.

SECOND PART SUMMARY

The telephone, which is referred to as the plain old telephone system (POTS), was originally an analog system. During the last decade, the telephone network has undergone many technical changes. The network is now digital as well as analog.

The telephone network is made of three major components: local loops, trunks, and switching offices. It has several levels of switching offices such as end offices, tandem offices, and regional offices.


MODELS


MODELS (3/6)


The United States is divided into many local access transport

areas (LATAs). The

services offered inside a LATA are called intra-LATA services.

The carrier that

handles these services is called a local exchange carrier (LEC).

The services between LATAs are handled by interexchange carriers (lXCs).

In in-band signaling, the same circuit is used for both signaling and data. In out-of- band signaling, a portion of the bandwidth is used for signaling and another portion for data.

The protocol that is used for signaling in the telephone network is called Signaling System Seven (SS7).

Telephone companies provide two types of services: analog and digital. We can categorize analog services as either analog switched services or analog leased services.

The two most common digital services are switched/56 service and digital data service (DDS).


MODELS


MODELS (4/6)


SUMMARY OF UNIT ONE: NETWORK MODEL

Data transfer using the telephone local loop was traditionally done using a dial-up modem.

The term modem is a composite word that refers to the two functional entities that make up the device: a signal modulator and a signal demodulator.

Most popular modems available are based on the V-series standards. The V.32 modem has a data rate of 9600 bps. The V32bis modem supports 14,400-bps transmission.

V90 modems, called 56K modems, with a downloading rate of 56 kbps and uploading rate of 33.6 kbps are very common. The standard above V90 is called V92.

These modems can adjust their speed, and if the noise allows, they can upload data at the rate of 48 kbps.

Telephone companies developed another technology, digital subscriber line (DSL), to provide higher-speed access to the Internet. DSL technology is a set of technologies, each differing in the first letter (ADSL, VDSL, HDSL, and SDSL. ADSL provides higher speed in the downstream direction than in the upstream direction.


MODELS


MODELS (5/6)


The high-bit rate digital subscriber line (HDSL) was designed

as an alternative to the T-l line (1.544 Mbps). The symmetric digital subscriber line (SDSL) is a one twisted- pair version of HDSL.

The very high-bit-rate digital subscriber line (VDSL) is an alternative approach that is similar to ADSL.

Community antenna TV (CATV) was originally designed to provide video services for the community. The traditional cable TV system used coaxial cable end to end.

The second generation of cable networks is called a hybrid fiber-coaxial (HFC) network. The network uses a combination of fiber-optic and coaxial cable.

Cable companies are now competing with telephone companies for the residential customer who wants high-speed access to the Internet.

To use a cable network for data transmission, we need two key devices: a cable modem (CM) and a cable modem transmission system (CMTS).


MODELS (6/6)


THE END OF UNIT- 1

NETWORK MODELS


Acknowledgement :

My Sincere Thanks To The Author Prof.BEHROUZ A FOROUZAN.

Because The Above Presentation Materials Are Heavily

Borrowed From His Textbook “Data Communication &

Networking” 4th Edition, publisher Tata McGraw Hill

By

Prof.Suresha V

92

Thank you


reach me at : [email protected]


Keep going…..

Ccn unit1 for 7th SEM EC by Prof. suresha V

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