Chapter 14, NEW TECHNOLOGY FAMILIARIZATION

Asynchronous Transfer Mode

Chapter 14

ATM(ASYNCHRONOUS TRANSFER MODE)

Contents Background information on ATM technology

Difference between STM & ATM

ATM protocol

Different switching

ATM interfaces and connections

ATM network architecture

ATM type of switches

ATM cell format, UNI/NNI format

ATM RM & layer functions

ATM benefits

ATM switch architecture

ATM services

Underlying transmission system for ATM

Objectives

After completion of this module you will be able to:

Understand the background information on ATM technology

Understand the difference between STM & ATM

Understand the ATM protocol

Understand the different switching

Understand the ATM interfaces and connections

Understand the ATM network architecture

Understand the ATM type of switches

Understand the ATM cell format, UNI/NNI format

Understand the ATM RM & layer functions

Understand ATM benefits

187 Prepared by RGM TTC, Chennai


Understand ATM switch architecture

Understand the ATM services

Understand the underlying transmission system for ATM



14.1 Introduction

14.1.1 Pre ISDN situation

1st generation switches are dedicated to specific purposes such as telephony, facsimile

and low speed data transfer used circuit switched telephone network. So high-speed data

transfer over this network is not possible due to lack of bandwidth, flexibility, quality of

transmission media and equipment. Then for the purpose of high-speed data transfer,

another network called packet switched network came into existence.

14.1.2 ISDN situation

ITU-T (the new avatar of CCITT) set new standards for public telecom network. In 1984,

ITU-T defined a new method called 2nd generation switch known as ISDN " a network

that provides end to end digital connectivity to support a wide range of services including

voice and non-voice service, to which users have access by a limited set of standard

multipurpose UNI". For this, 2 interfaces called BRI or BRA (192Kbps) and PRI or PRA

(2.048Mbps) are defined at the basic rate of 64Kbps. By this, maximum transmission is

restricted to 2Mbps only.

14.1.3 N-ISDN situation

With the basic bit rate of 64Kbps, the network can offer a maximum of 1.544Mbps

(called T1 link) or 2.048Mbps (called E1 link). So, such a type of working is called N-

ISDN. However with the concept of LAN, transmission of images with good resolution

may require higher bit rates. This leads the new conception and realization of 3 rd

generation switch, based on B-ISDN. ITU-T in 1993, defines B-ISDN as "a service or

system requires transmission channels capable of supporting rates greater than PRA or

PRI".



14.1.4 B-ISDN situation

So the concrete idea of B-ISDN was support to:

1. Add new high-speed channels to the existing channel spectrum.

2. Defines new broadband UNI (User Network Interface).

3. Rely on existing 64Kbps ISDN protocols and only modify or enhance them

when absolutely unavoidable.

So B-ISDN was perceived to replace the entire telephone system and all the

specialized networks with a single integrated network for all kind of information

transfer.

The services offered by B-ISDN include video-on-demand, full motion picture

from many sources, full motion multimedia electronic mail, CD quality music, LAN

interconnection, high speed data transport for industry and many other services that have

not yet even been thought of, all over the telephone line.

Hence B-ISDN is defined as "an ISDN system using transmission channels

capable of supporting rates that are greater than PRA".

14.2 ATM situation

The underlying technology that makes B-ISDN possible is ATM (Asynchronous Transfer

Mode).

Mode means specific method or way.

Transfer means transmission and switching aspects. Switching by means of Cell

Switching. Transmission by means of Primary rate of 155.52Mbps or above.

Asynchronous means information packets will be transferred based an irregular

or random occurrence pattern as they are filled according to the demand.

Hence "ATM is a method of transmission & switching of information in the form

of packets which may occur an irregular occurrence pattern as they are filled according to

the demand of the user".



14.3 STM

MUX

XY

AB

XY AB

Fig-1

In the above Fig-1, even though the Cell X and B are empty, they will also be

Multiplexed and sent on the output side. By this, the bandwidth is not used effectively.

14.4 ATM

MUX

XY

AB

Fig-2

Y A

In the above Fig-2, the empty Cells X and B are not at all transferred towards

output side. By this, the output bandwidth is effectively used. This technique is used in

ATM switching

Packet switching technology is used.

Statistical multiplexing (another name of Asynchronous Time Division

Multiplexing) is used.

Cell Relay method is used.



Hence ATM is a standardized technology that enables the convergence of a

variety of services such as:

Low bandwidth and Very high bandwidth.

Synchronous and Asynchronous.

Voice, Video and Data.

Constant Bit Rate (CBR) and Variable Bit Rate (VBR).

Real-Time (RT) and Non-Real-Time (NRT).

Slotted and Pocketsize.

Switched and Non Switched.

In addition, ATM is an independent of Transmission medium, which means the

medium can be Wire (Twisted Pair/Copper Pair/Co-axial/ Fiber) or Wireless.

ATM technology allows a variety of bit rates to be transported, with which

sophisticated bandwidth management enables the network to be more efficient and at the

same time, maintain a QoS (Quality of Service) that is custom suited to each other.

14.5 ATM Protocol

ATM is the protocol designed by ATM Forum and adopted by the ITU-T. ATM

can be thought of as the “Highway” of the information Super highway.

So ATM can do every thing that N-ISDN can do but with better quality.

In ATM System, the packet size is fixed to 53 octets known as a CELL. Any type

of traffic viz Voice, Data, Video, Synchronous or Asynchronous, Short or Long packets

can be converted into ATM Cells by a process known as emulation.

So ATM can also be called as Cell relaying technology or Cell switching

technology.

Can be called as B-ISDN services switch.

Primary rate of transmission in ATM is 155.52Mbps.



14.6 Cell Switching

Switching means creating a temporary connection between two or more devices linked to

the switch, a Hardware and/or Software devices. Traditionally, 3 methods of switching

have been important called Circuit Switching, Packet Switching and Message Switching.

14.7 Circuit switching

Circuit switching create a direct physical connection between two devices such as phones

or computers. As in Fig-3, devices A & G are connected by the switches 1,2 and 4 via

path I and III. Circuit switching is mostly used at the physical layer of OSI Model

1 2

3

4

A

B

C

D

E

F

G

I

III

II

Fig-3

14.8 Packet Switching

For Data communication Packet switching technology was designed. User data are

packetized and sent packet by packet using the path in shared manner. Two different

approaches are available under packet switching. One is called Datagram approach and

second is called Virtual circuit approach. The latter is used in ATM.

The identifier that is actually used for data transfer in Virtual circuit approach is

called the Virtual circuit identifier. A VCI is a smaller number that only has switch scope.

It is used by a frame.

When a frame arrives at a switch, it has one VCI. When it leaves, it has another

VCI. Fig-4 shows how the VCI in a data frame changes from one switch to another



XData 21 Data 88

VCI VCI

Fig-4

Switch

14.9 ATM Interfaces

ATM has 2 interfaces namely

1. User to Network Interface (UNI)

1. Private UNI

2. Public UNI

2. Network to Network Interface (NNI)

UNI is used between user and network where as NNI is used between networks.

14.10 ATM Connections

ATM or B-ISDN offers 2 types of connections called PVC & SVC and ATM services are

connection oriented.

14.11 Permanent Virtual Connection (PVC)

A source and a destination may choose to have a dedicated virtual circuit. In this case, the

corresponding table entry is recorded for all switches by the system administrator. An

outgoing VCI is given to the source and an incoming VCI is given to the destination. The

source always uses this VCI to send frames to that particular destination. The source

always uses this VCI to send frames to that particular destination. The destination knows

that the frame is coming from that particular source if the frame carries the corresponding



incoming VCI. In a simple word, PVC is like a Hotline/P Wire/ Point to Point/ Leased line

and the nature is static. Fig-5 shows the PVC setup.

A Bx x

xData 14

11

31

Data 34 Data 44

Data 54

41 51

21 22

Incoming OutgoingPort VCI Port VCI21 34 22 44

Incoming OutgoingPort VCI VCI11 14 31 34

PortIncoming OutgoingPort VCI VCI41 44 51 54

Port

Fig-5

14.12 Switched Virtual Circuit (SVC)

If a source needs connection with several destinations or any other destination, it needs a

PVC for each destination which is costly. An alternative approach is the SVC. So SVC

creates a temporary, short duration connection which exists only whenever data are being

transferred by the end users. In other words, this is dynamic in nature. This approach

requires a series of action called connection setup, setup acknowledgement, data transfer

and tear down phases. ATM supports both types of connections

14.13 ATM network architecture

ATM network consists of access devices called the end points, available at user end, are

connected through a interface called UNI to the ATM switch. Another ATM switch of the

network is connected through an interface called NNI. The architecture is shown in the

Fig-6.



1 2 3

A

B

C

D

E

F

EndPoints

UNI UNI

EndPoints

NNI NNI

Switch Switch Switch

NetworkATM

Fig-6

14.14 Virtual Path/Virtual Connection or channel or circuit/Transmission Path

Connection between two end points is accomplished through transmission path (TP),

virtual path (VP) and virtual circuit (VC).

A transmission path (TP) is the physical connection (wire/wireless) between an

end point and a switch or between two switches.

A TP is divided into several virtual paths (VPs). A virtual path provides a

connection or set of connections between two switches.

Within a VP, many circuits called virtual circuits (VCs) will be available which is

used for connection.

Cell networks are based on virtual circuits. All cells belonging to single message

follow the same VC and remain in their original order until they reach their destination.

TP, VP and VC are shown in Fig-7.



Transmission pathVP inside Trans Path

VC inside VP Which is inside Trans Path

Fig-7

14.15 VPI/VCI

In a virtual circuit network, to route data from one end point to another, the virtual

connection need to be identified. For this purpose, the designer of ATM, created a

hierarchical identifier with 2 levels called virtual path identifier (VPI) and virtual circuit or

channel identifier (VCI). The VPI defines the specific VP and the VCI defines a particular

VC inside the VP. Both the connection identifier are shown in Fig-8.

Transmission pathVPI inside Trans Path

VCI inside VPI Which is inside Trans Path

Fig-8

VP1

VP2

VP3

VC1VC2VC3

14.16 VP Switch/VC Switch

Most of the switches (Core switch) within typical ATM network are routed using VPI

(VP switch). (i.e) The switching can be taken place by changing the VPI but keeping VCI

within VPI intact. Such switches are called VP switch. If switching can be taken place by

changing both the VPI and VCI, then such switches are called VC switch. The switches at



end points (Edge switch) of the ATM network use both VPIs and VCIs (VC switch). Both

switches are shown in Fig-9.

VP and VC Switching

VCI 1 VCI 2 VCI 3 VCI 4

VPI 2VPI 3VPI 1

VPI 2

VPI 3

VPI 5

VPI 1

VPI 4

Port 1

Port 2

Port 3

VCI 1VCI 2

VCI 1VCI 2

VP Switch

VC Switch

VCI 3

VCI 4

VCI 1

VCI 2

VC Switch

Fig-9

14.17 ATM Transmission Rates

At present, rate of transmission is 155Mbps called primary rate. Higher order is also

possible in multiple of 4 times.

14.18 ATM Cell Format

ATM Cell consists of 2 fields called Header Field and Information Field as in Fig-10.

Fig-10


HEADER FIELD INFORMATION FIELD 5 OCTETS 48 OCTETS


14.18.1 Header Field

Header field is different for UNI and NNI in the ATM network

14.18.1.1 GFC ( Generic Flow Control - 4 bits)FC ( Generic Flow Control - 4 bits)

It is used to assist the customer network in the cell flow control, but not carriedIt is used to assist the customer network in the cell flow control, but not carried

through the network. through the network.

14.18.1.2 VPI/VCI (Virtual Path Identifier-8 bits/Virtual Channel Identifier-16 bits)

This label identifies a particular virtual path and virtual channel or circuit on a

transmission link. The switching nodes use this information and along with the routing

information established at connecting setup, routes the cells to the appropriate output

ports. The switching nodes changes the input value of VPI/VCI fields to new output

values. Since VPI field is 8 bits (at UNI) and VCI has 16 bits field, a host can have

theoretically 256 bundles, each containing up to 65,536 circuits.

8 VPI bits provide 28 = 256 bundles

16 VCI bits provide 216 = 65,536 circuits



14.18.1.3 CLP (Cell Loss Priority-1 bit)

Having one of the two values ‘0’ or ‘1’, the CLP indicates priority of a cell when

the network element has to make the decision to drop the cell when its throughput

bandwidth exceeds its transfer rate.

In congestion situations, cells with CLP =1 may be dropped and not transferred at

all.

14.18.1.4



PTI (Payload Type Identifier-3 bits)

It identifies the payload type i.e. whether the cell payload contains user data or

network information and also provides congestion identification.

14.18.1.5 HEC (Header Error Control-8 bits)

HEC code detects and corrects a single bit error or detects multi bit errors in the

header field. It is based on CRC-8 with the devisor polynomial as X8+X2+X+1.



14.18.2 Information Field (48 Octets)

CSI => Convergence Sub layer Indicator (1bit)

SN => Sequence Number (3bits)

SNP => Sequence Number Protection (3 bits)

The Information Field does not contain all the 48 octets of user data. One or two

octets are dedicated for administration and call sequence purpose.

The first octet (after the overhead bits or Header octets) consists of three sub

fields.

The first bit is known as the convergence sub layer indicator (CSI). It is used to

indicate whether the pointer is used or not.

The next three bits are sequential number (SN) from 000 to 111 used to detect the

type of cells.

The next three bits are the Sequence Number Protection (SNP). It performs error

detection on the CSI and SN sub fields.

One bit is not used at present.

The second octet is optional and is used as a pointer to mark the start of long

encapsulated messages.

48-octet information field is only scrambled.



14.19 Format

14.20 ATM Reference Model:

ATM functionality is organized in a stack of layers; each layer assigned a specific

function. It consists of three planes called

1) User Plane 2) Control Plane 3) Management Plane



Management Plane:

All the management functions that relate to whole system are located in the

management plane, which is responsible for providing coordination between all planes.

Two types of functions i) Layer Management ii) Plane Management.

Layer Management:

1.Management functions relating to resources and parameters residing in its

protocol entities.

2.Handles specific OAM information flow for each layer.

Plane Management

Management of all the planes for its proper functions.

Control Plane

Responsible for the call control and connection control functions.

These are all signaling functions for setup, supervise and release a call or

connection.



User Plane

Deals with transport of user information, flow control and recovery from errors.

14.21 ATM Protocol Layers

ATM standard defined 3 layers. They are from top to bottom, the AAL (ATM Adaptation

or Application Layer), the ATM Layer and the Physical Layer as in Fig-11

AAL

ATM

PHYSICAL Layer-1

Layer-2

Layer-3

Fig-11

Normally the end switches use all the 3 layers while the intermediate switches use

only the bottom 2 layers as in Fig-12

X XSwitch SwitchEnd

PointEnd

Point

AAL

ATM

PHYSICAL

AAL

ATM

PHYSICAL

ATM

PHYSICAL

ATM

PHYSICAL

ATM N/W

Fig-12



14.22 Functions Of Each Layer

14.22.1 Physical Layer

This Layer deals with issues related to physical connectivity of the transmission

medium and transmission of ATM Cells.

This layer is divided into 2 sub layers called

1.Physical Medium Dependent (PMD)

2.Transmission Convergence (TC)

Functions Of Physical Medium

It is the lowest sub layer and includes 2 functions namely

1.The PMD functions.

2.Bit timing functions.

PMD functions provide the bit transmission capability, including bit alignment.

Line coding and if necessary, electrical/optical conversions is performed by this layer. In

many cases PM will be an OFC. Other media such as coaxial and twisted pair cables are

also possible. The transmission functions are medium specific.

Bit timing functions are the generation and reception of waveforms suitable for

the medium, insertion and extraction of timing information, and line coding if required.

The TC sub layer performs 5 functions namely

1.Transmission frame generation & recovery.

2.Transmission frame adaptation is responsible for all actions to adapt the Cell

flow according to the payload structure of the transmission system (interface). Two

interfaces are defined namely (1) SDH based interface or Byte structured interface and

(2) Cell based interface.

Under SDH based interface, 155.520Mbps (STM-1) & 622.080Mbps (STM-4)

rates are recommended for UNI.

3. Cell delineation is the process, which allows identification of the Cell

boundaries.



4. HEC sequence generation/verification. This is the value for the 1st 4 octets of

the Cell header and inserts the result in the 5 th octet HEC field. This is capable of

detecting and correcting single bit error & detecting certain multiple-bit errors.

5.Cell rate decoupling. The insertion & discarding of idle Cells is called Cell rate

decoupling.

14.22.2 ATM Layer

It deals with flow issue of ATM Cells, Cell header related and path related issues.

Functions of ATM Layer

This layer is above the Physical Layer

This layer has got four functions:

1.Cell multiplex/demultiplex. VC and VP are multiplexed and demultiplexed.

2.VPI and VCI translation.

3.Cell header generation/extraction.

4.Generic Flow Control.

14.22.3 ATM Adaptation Layer (AAL)

This layer lies between ATM Layer and Higher Layer. It has two functions.

1. Segmentation And Reassembly (SAR)

2. Convergence Sub layer (CS)

1) Service Specific Convergence Sub layer (SSCS)

2) Common Part Convergence Sub layer (CPCS)

AAL can be classified by four methods namely

1. Based on Timing. Timing between source and destination required or not

required. Real time services like voice & video required timing syn where as non-real

time services like data transfer not required syn.

2. Based on Bit rate. Bit rate constant or variable. Switched speech has CBR

where as packet transfer has VBR.

3. Based on Connection. Connection oriented or not.

4. Based on Services offered. 5 layers called AAL1 to AAL5.



AAL Layer Support Acceptable

data from

Higher

Layer

CS Level Addition at

SAR Level

Output in

Bytes

AAL1 64Kbps

Voice/Video in

CBR

Bits stream Packet size

as 47

Bytes w/o

Header

One Byte

as Header

48

AAL2 No CBR, but low

bit rate & short

frame traffic like

mobile services

Short in

packets

44 Bytes

data and 3

bytes

Header

One Byte

as Header

48

AAL3/4 Connection

oriented/Connection

less

In packets

up to 64KB

44 Bytes

per packet

after

adding 4

Bytes each

as Header

and Trailer

Two Bytes

as Header

and two

Bytes as

Trailer

48

AAL5

(SEAL)

All types of traffic In packets

up to 64KB

- - 48

14.23 ATM Switch Type

Knockout switch, cross bar switch or single stage switch, shared memory switch, shared

medium switch, fully interconnected switch, space division switch, banyan switch or

multi stage switch, batcher-banyan switch and sunshine switch are the different type of

ATM switches. Batcher-Banyan switch is widely used



14.24 Benefit Of ATM2 Main benefits are 1) Traffic management 2) QoS

Traffic Management

Protects the network and the end system from congestion in order to achieve

network performance objectives

Promotes the efficient use of network resources

Mechanisms are both preventive and reactive

Fairness by identification and isolation of misbehaving traffic and per flow

processing

Parameters for traffic management

1) Connection Admission Control (CAC)

2) Usage Parameter Control (UPC)

3) Network Parameter Control (NPC)

4) Cell Loss Priority (CLP)

5) Traffic Shapping

6) Frame Discard

7) Feed Back Control

8) Network Resource Management

QoS contracts parameter negotiations are defined in UNI Ver 3.0, UNI Ver 3.1

and UNI Ver 4.0 (Ver 4.0 is the latest one) and PNNI Ver 1.0 signalling for native

ATM environment and LANE Ver 2.0 (Latest one) for non-native ATM

environment.

ATM QoS Parameters

Six parameters are defined for ATM QoS. They are 1) Negotiated parameter

(Dynamic nature-Sl.No 1,2 & 3) and 2) Non-Negotiated parameter (Static nature-Sl.No 4,

5 and 6)

Sl.No Parameter Abbreviation Meaning

1 Cell Delay Variation CDV Difference between a single

observation of Cell transfer

delay and the mean Cell transfer



delay on the same connection.

2 Cell Error Ratio CER Ratio of errored Cells to the

number of delivered Cells.

3 Cell Loss Ratio CLR Ratio of lost Cells to transmitted

Cells.

4 Cell Misinsertion Ratio CMR Number of misinserted Cells

per connection/second

5 Cell Transfer Delay CTD Arithmetic average of specified

number of Cell transfer delays.

6 Severely Errored Cell

Block Ratio

SECBR Ratio of number of Severely

errored Cellblocks to total

number of Cellblocks.

15.25 ATM QoS service classes

3 metrics were devised to give 3 different service classes such as Fastest traffic,

average traffic and best effort traffic under traffic contract scheme

Sl.No Metric Abbreviations Meaning

1 Peak cell Rate PCR The highest rate at

which traffic will

run for any length of

time (defined in

cells/sec)

2 Sustainable cell Rate SCR The mean rate at

which traffic ideally

will travel (defined

in cells/sec)

3 Maximum burst Size MBS The largest cell

burst that will be

tolerated by traffic

contract (defined in



cells/sec)

14.26 ATM Signalling concepts

VPI=0 and VCI=5 is used for default signalling channel

VPI=X and VCI=Y is used for data transfer

Any VPI and VCI=5 can also be used for signalling

Switching is done according to the called number within signalling message

Signalling purpose to establish, release and maintain the user communication

channel or path

14.27 ATM Switch Architecture

The basic function of the ATM switching system is to route the cells from the input port

to the appropriate output port of the switch. The ATM switching system must contain the

function defined by the U-Plane, C-Plane and M-Plane of the B-ISDN PRM in addition

to relaying of cells. Also the ATM system should support & implement the traffic control

function based on ITU-T & ATM-F recommendations.

All these functions are distributed within the ATM system switch architecture as

in the Fig-13 with the following functional parts:

1) Input Modules (IMs)

2) Cell Switch Fabric (CSF)

3) Output Modules (OMs)

4) Connection Admission Control (CAC)

5) System Management (SM)

6) Muliplexer/Demultiplexer (Optional)



Generic ATM Switch Architecture

IM

IM

IM

IM

SwitchingNetwork

(CSF)

OM

OM

Control

MUX

OM

CAC SM

NativeATM

NonNativeATM

Fig-13

Input Module (IM)

1) Handle i/c traffic

2) Conversion of optical to electrical signal

3) Extracting the digital bit stream

4) Identifying the cell boundaries

5) Extracting the ATM cells

6) Discarding the empty cells

7) Error checking the cell header

8) Traffic shapping

9) UPC/NPC verification from database & notification to SM

Cell Switch Fabric (CSF)

This is primarily responsible for transferring data cells between the IM & OM

after processing the signalling cells with the help of CAC & operation and maintenance

cells with the help of SM

It includes cell buffering, VPI and VCI translation, multicasting, broadcasting,

cell scheduling based on user priorities and congestion monitoring.

Output Module (OM)

1) It is the counter part of IM

2) Handles the outgoing traffic

3) Insertion of signalling/management cells received from CAC & SM into o/g

cell

4) New VPI/VCI allocation from database



5) Mapping of ATM cells

6) Filling up of empty cells

7) Line coding

8) Electrical to optical conversion

CAC

The signalling/control information is routed to CAC through CSF or from IM

directly. It performs the connection admission discussion and resource allocation for all

connections in the switch

SM

It is responsible for managing the entire switching system. It includes fault

management, performance management, configuration management, security

management, accounting management and traffic management by means of congestion

control. Also responsible to support Interim Local Management Interface for each UNI.

Mux/Demux

It is an optional item. It will be available only if non-native ATM devices are to

be interconnected with ATM switch.

Numbering Convention

It is defined as per ITU-T recommendation I-361 which says that:

Octets are sent in increasing order starting with octet 1. Therefore the header field

will be sent 1st followed by the information filed.

Bits within an octet are sent in decreasing order starting with bit 8.

So, for all fields, the 1st bit is the MSB.

CELL

A Cell is a block of fixed length. It is identified by a label at the ATM layer of the

B-ISDN PRM.

14.28 Types of Cell7 types of Cells are there namely

i) Idle Cell

ii) Valid Cell

iii) Invalid Cell



iv) Assigned Cell

v) Unassigned Cell

vi) Meta signalling Cell

vii) OAM Cell

Idle Cell

This is inserted or extracted by the physical layer in order to adapt the Cell flow

rate to the available rate of the transmission system.

Valid Cell

This is a Cell with no header error or with a corrected error.

Invalid Cell

This is a Cell with a non-correctable header error.

Assigned Cell

This is a valid Cell that provides a service to an application using the ATM layer

service.

Unassigned Cell

This is an ATM Layer Cell, which is not an assigned Cell.

Meta Signalling Cell

This is used for establishing or releasing a switched virtual connection,

Administration and Maintenance of ATM node and the network channel connection.

Permanent Virtual Channel connection needs no Meta signalling.

OAM Cell

This is used for Operation & Maintenance.

14.29 ATM Services

ATM services are classified into 4 categories.

Sl.no Name of services Uses Application

1 Conversational services

1.Bi-directional

Provides the interacting,

real-time end to end.

Voice services



2.Uni-directional Video telephony,

Videoconference.

2 Retrieval services

1. Selective

Data library services

stored in a central

places

Film, high resolution

images, audio and video

retrieval.2.All

3 Messaging services Not real time services.

Data may get stored in

nodes and forwarded

from location to

location

Message handling

services, mail services

4 Distribution services

a) W/o user-individual

presentation control

Cable TV transmission.

User has no control over

time or order of

presentation.

Stock market information,

weather broadcast,

newspaper services and

TV programs

b) With user- individual

presentation control

Information is

transmitted as a

sequence of frames with

cyclic repetition. User

has control over time or

order of presentation.

Inter active electronic

news paper

14.30 Underlying Transmission System For ATM Switch

SDH- Asper ITU-T recommendation, follows all countries except NORTH

AMERICA and JAPAN.

SONET-Asper ANSI recommendation, follows NORTH AMERICA and JAPAN.

BSNL implemented with SDH as in the Fig-14



ATMNode

ATMNode

ATMNodeATM

NodeSDHRING

ATM Switch With SDH Transmission Ring

Fig-14

14.31 ConclusionThe key to efficient utilization of the ATM networks is the integration of multiple

services over a common infrastructure. Traffic management with QoS plays a significant

role. ATM is going in a big way to play in different flavor like BB etc. To support this,

various native ATM & as well as non native ATM protocols are defined.


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Chapter 14, NEW TECHNOLOGY FAMILIARIZATION