1-Asynchronous Transfer Mode (ATM)

8/3/2019 1-Asynchronous Transfer Mode (ATM)

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Asynchronous Transfer Mode

(ATM)



By.

P. Victer Paul

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Agenda

Definition

Basic characteristics

Why asynchronous

How to access the network

Service Categories

Connections Protocol Architecture

pros & cons

Troubleshooting



ATM – definition

"A transfer mode in which information is

organized into cells; it is asynchronous in the

sense that the recurrence of cells containinginformation from an individual user is not

necessarily periodic".



ATM Characteristics

ATM uses packet switching with fixed length packetof 53 bytes – CELLs. Each cell has a 5-byte headerand 48-byte payload

ATM uses Virtual Circuits

ATM can run over any physical layer. Often runsover fiber optics using the SONET standard at speedsof 155.52 Mbps, 622 Mbps and higher



ATM Characteristics

A Cell network uses the cell as the basic unit of dataexchange. A cell is defined as a small, fixed-sizedblock of information

ATM uses asynchronous TDM – to multiplex cellscoming from different channels

Uses fixed slots (size of cells) Fills a slot with a cell from any input channel that

has a cell

– slot is empty if none of the channels has a cell

to send



Asynchronous Transfer Mode

(ATM)

M UX

Wasted bandwidth

4 3 2 1 4 3 2 1 4 3 2 1



ATM Access

ATM is a cell-switched network.

The user access devices, called the endpoints, are

connected through a user-to-network interface (UNI)to the switches inside the network.

The switches are connected through network-to-

network interfaces (NNIs).



STDUCTURE

X

X

X

X

X

X

X

X

X

PrivateUNI

PublicUNI

NNI

PrivateNNI

Private ATMnetwork

Public

UNI B-ICI

Public ATMnetwork A

Public ATMnetwork B



ATM Connections

two levels of ATM connections:

virtual path connections

virtual channel connections

indicated by two fields in the cell header:

virtual path identifier VPI

virtual channel identifier VCI



Physical Link

Virtual Paths

Virtual Channels



ATM Service Categories Real-time services

Constant bit rate – uncompressed audio/video info

Videoconferencing, TV, pay-per-view, VOD, etc.

rt-Variable bit rate

Non-real-time services

nrt-VBR – high end system QoS, critical response time

Bank transactions, airline reservations, etc.

Unspecified bit rate – best-effort service

e.g. text/image messaging, telecommuting

Available bit rate – bursty apps requiring reliable end-to-endconnection

e.g. LAN, router-to-router reliability



ATM Protocol Architecture

P l a n e m a n

a g e m e n t

Management plane

Control plane User plane

Physical layer

ATM layer

ATM adaptation layer

Higher layers Higher layers

L a y e r m a n a g e m e n t



adaptation layer: only at edge of ATM network

data segmentation/reassembly

roughly analogous to Internet transport layer ATM layer: “network” layer

cell switching, routing

physical layer

Physical layer

ATM layer

AAL user



Pros & cons higher transmission speeds

quality of service

bandwidth-on-demand

application-independent

Cost

Complexity Availability



Troubleshooting

Performing Basic Interface Checks

Determining Network Connectivity

Performing Loopback Tests Troubleshooting 155-Mbps and 622-Mbps Interfaces

Troubleshooting T1 and E1 Interfaces

Troubleshooting DS3 and E3 Interfaces

Troubleshooting CBR T1 and CBR E1 Interfaces Troubleshooting 25-Mbps Interfaces



References:

1. Asynchronous Transfer Mode (ATM) fundamentals, white paper from Internation

Engineering Consortium

2. ATM tutorial-fnc educational services

3. Higher Layer Protocols:TCP/IP and ATM- Eytan Modiano,Massachusetts

Institute of Technology

4. ATM Switch Troubleshooting Guide-Cisco

1-Asynchronous Transfer Mode (ATM)

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