This document provides an overview of Asynchronous Transfer Mode (ATM). It discusses how ATM was developed to allow telephone networks to carry different types of traffic beyond just voice calls. The key aspects of ATM covered include its cell-based format and connection-oriented design. Quality of service is handled through permanent and switched virtual connections. While ATM provided capabilities for multimedia networking, its complexity and costs prevented it from widespread adoption compared to other technologies.

1. Data Communication and Networking II
Asynchronous Transfer
Mode (ATM)
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)

2. Objectives Overview
Brief Intro to ATM
Issues driving LAN
changes to high
capacity
Transmissions
ATM LAN
Configuration
ATM Basic Cell
Format
ATM Protocol
Architecture
Conceptual
Model/Network in
ATM
ATM QoS and
Challenges
Data Communication and Networking II: Asynchronous Transfer
Mode (ATM)
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3. Asynchronous Transfer Mode
Brief Introduction to ATM
• By the mid 1980s, three types of communication networks
had evolved.
• The telephone network carries voice calls, television
network carries video transmissions, and newly emerging
computer network carries data.
• Telephone companies realized that voice communication
was becoming a commodity service and that the profit
margin would decrease over time.
• They realized that data communication was increasing.
• The telecommunication industry decided to expand its
business by developing networks to carry traffic other than
voice.
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Data Communication and Networking II: Asynchronous Transfer Mode
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4. Asynchronous Transfer Mode
• Wide Area Network Technologies
– Dialups
– X.25
– Frame Relay
– Asynchronous Transfer Mode (ATM)
– Synchronous Optical Network (SONET)
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Data Communication and Networking II: Asynchronous Transfer Mode
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5. Asynchronous Transfer Mode
• Telephone Network Transmission WAN links
– Asynchronous Transfer Mode (ATM)
• Switching transmission technology
– Synchronous Optical Network (SONET)
• Transmission technology
• Synchronous Transfer Mode (STM)
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Data Communication and Networking II: Asynchronous Transfer Mode
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6. Asynchronous Transfer Mode
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
• Wide Area Network Technologies Bandwidths
- Dialups to ATMs

7. Asynchronous Transfer Mode
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
• Wide Area Network Technologies Bandwidths
- SONET (STM)

8. Asynchronous Transfer Mode
Brief Introduction to ATM - Goals
• Universal Service
• Support for all users
• Single, unified infrastructure
• Service guarantees
• Support for low-cost Devices
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)

9. Asynchronous Transfer Mode
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
Issues Driving LAN changes
• Traffic Integration
– Voice, video and data traffic
– Multimedia demand
• One-way batch (web traffic)
• Two-way batch (voice messages)
• One-way interactive (internet multicast backbone – Mbone)
• Two-way interactive (video conferencing)
• Quality of Service guarantees (ex. Limited jitters, non-
blocking streams or buffering)
• LAN Interoperability (compatibility with any device make)
• Mobile and Wireless nodes

10. ATM LAN Configuration
Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
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11. ATM Basic Cell Format
• ATM technology is a form of Virtual Packet Switching
that divides all data into small, fixed-size packets
called Cells
• Connection-Oriented Service
• Each ATM Cell contains 53 octets
• 5 octets for header messages
• 48 octets for actual transmitted data
Data Communication and Networking II: Asynchronous Transfer
Mode (ATM)
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12. ATM Conceptual Model
Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
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• ATM Network is organized as a hierarchy
– User’s equipment connects to networks via a UNI (User-
Network Interface)
• Creating Permanent Virtual Channel (PVC) for communication
– Connections between provided networks are made
through NNI (Network-Network Interface) – ATM switch
• Creating Switched Virtual Channel (SVC) for communication
• This establish the connection-oriented channel
before any cells are sent

13. ATM Network
Data Communication and Networking II: Asynchronous Transfer
Mode (ATM)
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14. ATM Connections
Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
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• Two level of ATM connections:
– Virtual path connections
– Virtual channel connections
• Indicated by two fields in the cell header:
– Virtual path identifier (VPI) – 8 bits
– Virtual channel identifier (VCI) – 16 bits

15. ATM Virtual Connections
Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
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• Vast majority of ATM networks will run on optical fiber networks with
extremely low error rates.
• ATM must support low cost attachments

16. ATM Virtual Connections
Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
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17. ATM Virtual Connections
Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
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18. ATM Virtual Connections
Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
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19. ATM Virtual Connections (UNI Cell Format)
Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
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ATM Cell Headers
GFC (Generic Flow Control)
VPI (Virtual Path Identifier)
VCI (Virtual Channel Identifier)
PT (Payload Type)
CLP (Cell Loss Priority)

20. ATM Protocol Architecture
Protocol Layers
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)

21. ATM Protocol Architecture
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
• Physical Layer
– The lowest layer in the ATM protocol
– It describes the physical transmission media
– We can use shielded and unshielded twisted pair, coaxial cable, and fiber-
optic cable.
• ATM Layer
– It performs all functions relating to the routing and multiplexing of cells over
VCs.
– It generates and remove header contents destine to the Adaptation Layer
– Maintains a table which contains a list of VCIs.

22. ATM Protocol Architecture
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
• ATM Adaptation Layer (AAL)
– Top layer in the ATM protocol Model
– It converts the submitted information into streams of 48-octet segments
and transports these in the payload field of multiple ATM cells
– Define into 5 classes of service types referred as AAL1-5
• AAL1 and 2 provides connection oriented service types in constant bit
rate (CBR) and variable bit rate (VBR) respectively
• AAL3 – 5 provides non real time bit rate service types

23. ATM Adaptation Layer Service Categories
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)

24. ATM Quality of Service (QoS)
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
• Quality of Service (QoS) requirements are handled at
connection time and viewed as part of signaling
• ATM provides permanent virtual connections and
switched virtual connections
– Permanent Virtual Connections (PVC)
• set up manually by network manager
– Switched Virtual Connections (SVC)
• set up and released on demand by the end user via signaling
procedures

25. ATM Challenges
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
• ATM has not been widely accepted. Although some
phone companies still use it in their backbone networks
• The expense, complexity and lack of interoperability with
other technologies have prevented ATM from becoming
more prevalent

26. ATM Challenges
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)
• Expense: ATM switch costs much more than inexpensive
LAN hardware
– In addition, the network interface card needed to connect a
computer to an ATM network is significantly more expensive
than a corresponding Ethernet NIC
• Connection Setup Latency: ATM’s connection-oriented
design introduces significant delay for distant
communication
• Complexity of QoS: The complexity of the specification
makes implementation cumbersome and difficult. Many
implementations do not support the full standard

27. Reading & Reference Material
• Data and Computer Communications, 8th Edition
by William Stallings
– Chapter 11.1 - 5
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Data Communication and Networking II: Asynchronous Transfer Mode
(ATM)