This document provides an overview of ATM (Asynchronous Transfer Mode) technology. It discusses the basic concepts of circuit switching, packet switching, and virtual circuit approaches. It then describes ATM including that it is connection-oriented, uses fixed size 53 byte cells, and operates at speeds of 155Mbps or 622Mbps. It outlines the ATM layers including the physical layer, ATM layer, ATM adaptation layer, and upper layers. It also discusses AAL types and the advantages of ATM in supporting different traffic types and efficient bandwidth usage.

1. Module 2
WAN Technology
Ms. Pradnya Saval

2. Contents
• Introducing ATM Technology
• Need and Benefit
• Concept of ATM
• Faces of ATM
• Why ATM?
• BISDN Reference Model
• ATM Layer
• ATM Adaptation Layer

3. Basic Concepts
• Types of Switching:
• Circuit switching
• Packet switching
• Virtual circuit approach
• Datagram approach
• Message switching

4. Introduction to ATM
• Asynchronous Transfer Mode (ATM) is an ITU-Telecommunication Standard.
• It is connection oriented network.
• It can transmit all types of data. E.g.: text, audio, video
• Data is transmitted into fixed size packets called as cell which is 53 bytes long 5
bytes as header and 48 bytes of data).
• ATM uses virtual circuit approach and the packets are always delivered in order in
which it is send.
• It operates on 155Mbps or 622Mbps speed.

5. Concept of ATM
• Cells (data transfer units – 53 bytes)
• ATM Layers
• Class of Services
• Asynchronous Data Transfer
• Connection Type (connection oriented)
• Transmission Medium (CAT6 cable, a fiber cable, a WAN and even packaged
inside payload of other carrier systems.)

6. ATM Layers

7. ATM/BISDN Reference Model

8. Physical Layer
• ATM cells can be carried by any physical layer carrier.
• Physical Medium Dependent (PMD)
• It interfaces to the actual cables used.
• Manage the bit ate, data rate and bandwidth of the transmission
• Transmission Conversion (TC)
• Convert the bit stream into cell stream of 53 bytes and send to the upper ATM layer.

9. ATM Layer
• Functions:
• Cell Management
• Virtual circuit and path management
• Connection orientation
• Congestion Control

10. ATM Layer

11. ATM Header

12. ATM Adaptation Layer
• Sublayers:
• Segmentation and Reassembly (SAR)
• Breaks up packets into cells on transmission and puts them back together in
the destination side.
• Convergence Sublayer (CS)
• Provide an interface to perform various error handling and timing
mechanisms for different types of data to be transferred.

13. Upper Layers
• User Plane:
• Data Transport
• Error Control
• Flow Control
• Control Plane:
• Connection Management for users

14. AAL Types

15. AAL1

16. AAL2

17. AAL3/4

18. AAL5

19. Advantages of ATM
• It is optimized to transport voice, data and video i.e. single network for everything.
It is used for mixed traffic, real-time and non real time traffic types.
• It provides the dynamic bandwidth that is particularly suited for bursty traffic.
• Uniform packet size ensures that mixed traffic is handled efficiently.
• Small sized header reduces packet overload, thus ensuring effective bandwidth
usage.
• It enables efficient use of network resources using bandwidth on demand concept.
• It uses simplified network infrastructure.