High Speed Networks lecture 5

7/29/2019 High Speed Networks lecture 5

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High Speed Networks

Lecture 5

Uday Prakash

Uday3prakash@ gmail.com


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Traditional Telephone Network VS

Integrated Digital Network

Traditional Telephone Networks

Separately designed and administrated transmission and switchingsystems

Demultiplexing and demodulating are necessary at each switchingcenter

A repeated process results in an accommodation of noise as well as cost

Integration of transmission and switching systems Achievable when both systems are digital

Using PCM modulation and TDM multiplexing

Switching without decoding along the way Separate multiplex/demultiplex channel banks are not required


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History of ISDN

Developed by CCITT (Comate Consultative International

Telephonique Telegraphs) to limitation of POTS (Plane old

Telephone system).

Original document was I.120 version in 1984.

Early 1990s produced NI-1version.

Every country has its own ISDN standards, called National

ISDN standards (NIs).

More recently NI-2 also manufactures worked with phonecompanies to simplify ordering.


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AnalogNetworks

DigitalNetworks

Low capacity copper cables---high capacity optical fibers. Electromechanical analog space division switching system-

Electronic digital time division switching

Channel associated signaling--common channel signaling.

Reduced network configuration More than one connection to the upper level of hierarchy


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Voice Communication over an

Analog Telephone Network


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Voice and Data Communication

over an Analog Telephone Network


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Analog and Digital Services

over the Telephone Network


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The Integrated Digital Network

Analog telephone network

Space-divisionswitch

Multiplex and modulate signalsDemultiplex and demodulate signals

PCM: pulse-code modulation


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Digital refers to its purely

digital transmission

Use of an analog telephone modem

for Internet access requires that

ISPs modem which converts thedigital content to analog signals

before sending it and the user's

modem then converts those signals

back to digital when receiving.

When connecting withISDN there is no digital to

analog conversion.


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Switching Network

Data links used for common channel signalling

between digital exchanges form a separate

signalling networks.

As signalling network uses transmission bearer

network channels, synchronizing network is

deserved to synchronize all PCM frames, to avoid

congestion.

Administrative network is to used to connect the

remote operations and management centers to the

nodes of the PSTN.

All these four networks uses the channels in the

basic transmission bearer network.


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ISDN


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Integrated Services Digital Network

Support a wide range of voice and non-voice

applications in the same network

Service integration for provision of a range of

services using a limited set of connection types

and multipurpose user-network interface

arrangements.

Support applications including Switched

(circuit switched, packet switched or their

concatenation) and non-switched connections.

Modem is not necessary, as it supports digitaltransmission of all types of data (including

voice). This also results in very short call setup

time between two ISDN subscribers.


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Evolution of ISDN I.120

Transition from existing network to a comprehensive ISDN may require a

period of time extending over one or more decades.

Interworking must be done during this period.

Based on concept developed for IDNs, involving progressively

incorporating additional functions and network features. In the evolution of ISDN, digital end to end connectivity will be obtained

via plant and equipment used in existing networks, such as digital

transmission, time-division multiplexing switching and/or space division

multiplex switching.


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NETE0510: Communication Media andData Communications 14

Principles of ISDN1. Support of voice and non-voice applications using a limited

set of standardized facilities Defines the purpose of ISDN and the means of achieving it

2. Support for switched and non-switched applications

Both circuit-switched and packet-switched connections

Support non-switched services in the form of dedicated lines

3. Reliance on 64-kbps connections

Fundamental block of ISDN

64 kbps were chosen because it was the standard rate for digitized

voice


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NETE0510: Communication Media andData Communications 15

Principles of ISDN (contd)4. Intelligence in the network

Sophisticated serviced beyond simple setup a circuit-switched call

Sophisticated network management and maintenance capabilities

Use of SS7 ( (common channel) signaling system number 7) and intelligentswitching nodes in the network

SS7 is a set of telephonysignaling protocols which are used to set up the vastmajority of the world's

public switched telephone network telephone calls.

5. Layered protocol architecture

User access to ISDN protocol is a layered architecture that can be mappedto OSI model

Standards can be developed independently for various layers andfunctions

6. Variety of configurations More than one physical configuration is possible for implementing ISDN


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ISDN Services


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Broad aspects of ISDN in I.121


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ISDN protocols

E-series protocols Telephone networkstandards for ISDN.

I-series protocols Specify ISDN concepts

and interfaces. Q-series protocols Standards for ISDN

switching and signaling.

Operate at the physical, data link, and networklayers of the OSI reference model


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Integrated Services Digital Network Standard interfaces between the user an

d the network include functional units,as:

1. Exchange Termination(ET) End userconnectivity.

2. Line Termination (LT)---BRI or PRI accessprovisioning.

3. Network Termination(NT1)-terminatesaccess line at customers end.

4. Network Termination(NT2)---enablesswitching functions to be performed.

5. Terminal Equipment (TE1)provisioning offunction required to handle layer 1, 2 & 3protocols.

6. Terminal Equipment(TE2)

providesfunctions corresponding to capabilities ofexisting equipments which do not conformto ITU-T standards.

7. Terminal Adapter (TA)converts layer1,2&3 protocols of TE2 into those of TE1,to enable equipment on TE2 to operateover the ISDN.


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ISDN Reference Points-interfaces

U - Two wire cable that connects thecustomers equipment to thetelecommunications provider

R - Point between non-ISDN equipment (TE2)and the TA

S - Four-wire cable from TE1 or TA to theNT1 or NT2

T - Point between NT1 and NT2


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Analogy

NT-1 (Network Terminator-1)An NT-1 is an interface box that converts ISDNdata into something a PC can understand (andvice versa). It works a little like a cable TVdescrambler for ISDN signals, and is oftenbuilt into ISDN adapters.

TA (Terminal Adapter)

This chunk of hardware converts the data itreceives over ISDN to a form your computercan understand. Sometimes mistakenly calledan ISDN modem or a digital modem, aterminal adapter handles data digitally anddoes not need to modulate or demodulate an

analog signal. Terminal adapters can be aninternal board or an external board thatconnects to the computer through the serialport.


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The User Interface


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The User Interface (contd) User has access to ISDN via a local interface to a digital pipe.

Pipes of various sizes are available to satisfy different needs

Pipe to the users promises has a fixed capacity but the traffic on the pipemay be a variable mix up to the capacity limit

ISDN requires control signals to instruct how to sort out the time-

multiplexed data and provide the required services Control signals are multiplexed onto the same digital pipe.

Recommendation from I.410: more than one size of pipe is needed

A single terminal (e.g. a residential telephone)

Multiple terminals (e.g. a residential telephone, PC, and alarm system)

A network of devices attached to a LAN or PBX (ISDN gateway)


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The User Interface (contd)


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ISDN Protocols at the user-network interface


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ISDN Architecture


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ISDN Architecture (contd) Physical interface provides a standardized means of attaching

to the network

The interface supports a basic service consisting of three time-multiplexed channels, two at 64 kbps and one at 16 kbps

In addition, there is a primary service that provide multiple64-kbps channels

An interface is defined between the customers terminalequipment (TE) and a device on the customers premises,known as a network termination (NT)

The subscriber loop is the physical path from the subscribersNT to the ISDN central office Must support full-duplex digital transmission for both basic and

primary data rates


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ISDN Protocol Operating OSI Layers 1 Through3

Physical layer ISDN protocols BRI (ITU-T I.430) / PRI (ITU-T I.431)

Defines two ISDN physical layer frame formats

Inbound (local exchange to ISDN customer)

Outbound (ISDN customer to local exchange )

Data link layer ISDN protocols

LAPD signaling protocol (ITU-T Q.920 for BRI and Q.921 for PRI) for transmitting

control and signaling information over the D channel

LAPD frame format similar to ISO HDLC frame format

Network layer ISDN protocols

ITU-T I.930 and ITU-T Q.931 defines switching and signaling methods using the D

channel.

Note: With Q.921/Q.931 the second digit indicates the OSI layer.


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ISDN Physical Layer

ISDN physical-layer frame formats are 48 bits long, of which 36 bits represent data


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ISDN Data Link Layer

Frame format is very similar to that of HDLC


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ISDN Network Layer

Two Layer 3 specifications are used for ISDN signaling: ITU-T I.450 (also known as ITU-T Q.930) ITU-T I.451 (also known as ITU-T Q.931)

Together, these protocols support: User-to-user circuit-switched connections

User-to-user packet-switched connections

A variety of standards for: Call establishment

Call termination


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Call Reference Field

Information Elements


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Information Element Types


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Addressing in ISDN


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ISDN Encapsulation

The two most common encapsulations: PPP

HDLC

ISDN defaults to HDLC.

PPP is much more robust. Open standard specified by RFC 1661

Supported by most vendors


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Channels of ISDN

B (Barrier or Bearer) Channel carries voice, data, video etc. This Channel functions at a constant 64 kbps. This channel can be usedfor packet and circuit switching applications.

64k bps per channel

The two B channels can be inverse multiplexed or boded together Achieve a maximum aggregate communication speed of 128 Kbps

D (Denial or Delta) channel is used to convey user signaling messages. This type channel used out of band signaling . This meansthat network related signals are carried on a separate channel than used data.

16 Kbps Entire bandwidth is not used for signaling purpose

Excess of 9.6 Kbps is available for packet switched data transmission applications

Excess bandwidth usage Climate control, security alarm system etc.

D Channel is packet switched Excess capacity can be utilized for packet switched applications

H channels have a considerably higher transfer rate than B channels. These channels effectively meet the needs of real time videoconferencing, digital quality audio and other services requiring a much higher bandwidth. H channel sustains rates of approximately1920 mbps.


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Integrated Services Digital Network

Something more(Supplementary

services) than the services carried by

PSTN.

In PRI, less than 30 or 23 channels

can be provided to obtain channels

with greater digit rates for broad

applications, as:

H0 channel at 384 kbps.

H11 channel at 1536 kbps(for 1.544

Mbps access.

H12 channel at 1920 kbps(for 2.048

Mbps access).

BRI standardized as ITU-T I.420

PRI standardized as ITU-T I.421


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Basic Rate Interface Basic Rate Interface (BRI)

Two 64 Kbps B channels, one 16 Kbps D channel, and 48 Kbps worth of framing andsynchronization.

Available data bandwidth: 128 Kbps (2 x 64 Kbps)

User bandwidth: 144 Kbps (128 Kbps + a 16 Kbps D channel)

Total line capacity: 192 Kbps (144 Kbps + 48 Kbps framing)

Each B channel can be used for separate applications Such as Internet and Voice

Allows individual B channels to be aggregated together into aMultilink channel


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Inverse Multiplexing of B Channels

B (64 Kbps)

B (64 Kbps)

128 Kbps 128 Kbps

Inverse Multiplexers


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BRI Frame


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Primary Rate Interface

Primary Rate Interface (PRI) A PRI connection can assign various 64 Kbps channels to both ISDN and analog modem connections

B channels can be combined together to increase the aggregate communication speed

North America and JapanPRI service has 23 64 Kbps B channels, one 64 Kbps D channel, and 8Kbps of synchronization and framing for a total bit rate of up to 1.544 Mbps (same as T1)

Europe, Australia, and other parts of the worldPRI service has 30 64 Kbps B channels, one 64 Kbps Dchannel, and 64 Kbps of framing and synchronization for a total bit rate of up to 2.048 Mbps (same asE1)

Aggregate speed of PRI from all 23 B channels and the single D Channel is computed as follows: 23 * 64 + 64 + xx = 1.544 Mbps

Each B channel to be used for separate applications including voice, data andInternet

Multiple B channels can be Multilinked together


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Bonding of B Channels or BOD

(Bandwidth on Demand)

B (64 Kbps)

B (64 Kbps)

64- 128 Kbps 64- 128 Kbps

Inverse Multiplexers with Dynamic Bonding

Channel Bonded on Demand


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PRI Frame


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Benefits of ISDN The principle benefits of ISDN to the customer can be

expressed in terms ofcost savings and flexibility

Integrated voice and data means that the user does not haveto buy multiple services to meet multiple needs

Access charges to a single line only

Purchasing services based on actual needs

Product diversity, low price, and wide availability ofequipment.


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Bit Rates for Different Applications


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Conversational (or Interactive) Services Real time end to end information transfer

Can be bidirectional or Unidirectional.

Telephone, Tele-education, video conferencing etc.

Messaging Services Communication via storage units (mailbox etc)

Emails, Video Mails Retrieval Services

Provide users with capability to retrieve information stored elsewhere

High Resolution Image Retrieval, Document Retrieval Services.

Distributed Services Video and Audio transmission services.

Electronic Newspaper

Video Services: TV Program Distribution

Digital Video Library

B-ISDN Services


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B-ISDN Access Schemes

R i f Vi l


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Requirements of Virtual

Circuit Technology for B-ISDN

Performance Requirements

Support for flexible bandwidth (Variable Access Rate)

Limited Error Rate

Bit Error Rate < 10-7 to 10-10

Packet Loss Rate < 10-5 to 10-7

Limited Delay and Delay Variation (Jitter)

delay < 25 ms for telephony limited delay for real-time applications

limited delay-variation for voice communication


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ATM : Solution for B-ISDN

Suitable for both real-time and non real-time

applications

Suitable for both loss-sensitive and loss-insensitive

applications Seamless networking

LAN to MAN to WAN

to carry Voice, Telephony, Multimedia, Data traffic


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ATM Concepts

ATM is based on Virtual Circuit Technology

Virtual Circuits have many advantages over

Datagram and Circuit Switching

Similar to Circuit Switching, ATM uses signalingprotocol to establish Circuit before data

communication commences.

Unlike Circuit Switching, ATM is based on

Statistical Multiplexing (Similar to Packet

Switching)


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ATM Concepts

In order delivery of Cells due to Virtual circuits No error protection or flow control on a link by link basis

Links are assumed to be high quality with low bit error rate

Preventive actions: Proper resource allocation and queue

dimensioning to reduce packet loss End-to-End error protection and recovery.

Flow control by input rate control and capacityreservation

Congestion control : Avoid congestion Drop cells when congestion occurs

Fixed size packets called Cells size 53 bytes = 48 bytes payload + 5 bytes header


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Cell Size

Based on :

Transmission efficiency

End-to-end delay

Packetization delay

Transmission delay

Switching delay


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Why Small Cells ?

Overhead Delay

%Ove

rhead

Delay(m

s)

Payload (bytes)

0 20 60 80


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Cell Size: 32 bytes or 64 bytes?

Cell size of 32 and 64 bytes:

64 bytes cells have better transmission efficiency

32 bytes cells have small delay

both sizes are integer power of 2 Europe wanted 32 bytes size, US and Japan wanted

64 bytes size

Compromise: 48 bytes


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ATM Cell Format

Header :5 bytes Payload (Information) 48 bytes

GFC VPI VCI PT HEC

VPI VCI PT HEC

12 16 3 1 8 bits

CL

P

CLP

4 8 16 3 1 8 bits

at

UNI

atNNI

GFC : Generic Flow Control VPI : Virtual Path IdentifierVCI : Virtual Circuit Identifier PT : Payload TypeCLP : Cell Loss Priority HEC : Header error CheckUNI : User Network Interface NNI : Network-Network Interface


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ATM Concepts

Reduced header functionality

Provision for multiplexing, head-error detection /

correction and limited control and maintenance

function

No sequence number

No destination and source address

Header Payload

5 bytes 48 bytes

h


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Asynchronous

Multiplexing of Cells

Data

Video

Cells

Multiplexer

Packetizer

Digital Pipe

Voice


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Features of ATM

Simple queue management and Cell processing

due to the fixed size cells

Suitability for

delay sensitive and loss insensitive traffic delay insensitive and loss sensitive traffic

Quality of Service (QoS) class support

Switched Access Multiple Access Speeds (25 Mbps - 155 Mbps)

Easily Scalable


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ATM

Physical Layer


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ATM Physical Layer : Introduction

Physical medium to carry ATM cells

Two sub layers

Transmission convergence (TC) sub layer Physical Medium Dependent (PMD) sub layer


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PMD Sublayer

Physical Medium Dependent Sublayer

Fiber, Twisted pair, Coax, SONET, DS3

Functions

Bit timing Line coding


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Cell-Stream Physical Layer

cells are transmitted as a stream without any

regular framing

OAM cells are identified by VPI:0, VCI:9

Synchronization is achieved by TransmissionConvergence Sub-layer

Cell


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Physical Medium Choices

Plesiochronous Digital Hierarchy (PDH) based

Interfaces

uses existing transmission network infrastructure DS1(1.544Mbps), E1 (2.048 Mbps), E3 (34.368

Mbps) , DS3 (44.736 Mbps), E4 speeds

Cell Delineation and Synchronization with HEC

25.6 Mbps UTP


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SONET / SDH Based

Physical LayerSynchronous Optical Network: (SONET)

Synchronous Digital Hierarchy (SDH)

Lower speed ATM streams can be multiplexed overhigher speed SONET streams

SONET supports a hierarchy of digital signals with abasic rate of 51.84 Mbps

Based on Time Division Multiplexing

H4 octet in the path header indicates offset to theboundary of the first cell following H4

Parts of a cell may be carried over two successiveSONET frames


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SDH Physical Layer

for ATM The most common physical layer to transport

ATM cells in public networks

Standards are defined for encapsulation of ATMcells in SDH (SONET) frames


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SDH Physical Layer

for ATM

Total : 9 Rows * 270 Columns

STM-1/STS-3c : 9*260*8/125 sec=145.76 Mbpspayload

Path

Overhead


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Cell Delineation

Identifies cell boundaries in a cell stream

Physical layers may use their own mechanisms

SONET uses H4 pointer

CCITT Recommended HEC-based Algorithm Generic

Can be used with cell-stream when there is no framing

structure

Contrast with Marker based framing

C ll D li ti b


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Cell Delineation by

HEC Field

HUNT PRESYNC

SYNC

Incorrect HEC

correct HEC

bit-by-bitcheck

cell-by-cellcheck

consecutiveincorrect HEC

consecutivecorrect HEC

Initially HUNT state

Bit-by-bit check to match

computed HEC with thereceived HECCCITT recommendation < 7 < 6


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Cell Payload Scrambling

At source, scramble the cell payload

At receiver, descramble the cell payload

To increase the security and robustness

To protect against malicious users or unintendedsimulation of a correct HEC in the information field


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Summary

Wide range of Physical Interfaces are available :

DS1 to STS-12

ATM Cells can also be carried over (standards are

being defined) Satellite

Wireless

Two Sublayers : Convergence Sublayer andPhysical Medium Dependent sublayer

R f


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References

ITU-T ISDN standards, http://www.itu.int/rec/T-REC-I/en.

Sumit Kasera, ATM Networks-concepts and Protocols, 2e,

Tata McGraw Hill publications, ISBN-10: 0-07-058353-6.

Harry Perros, ATM Networks.

High Speed Networks lecture 5

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