ASYNCHORONOUS TRANSFER MODES

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ASYNCHORONOUS TRANSFER MODES

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Points to be discussed are

• Definition
• ATM standard
• ATM network
• ATM interfaces
• ATM cell
• ATM Adaptation layer(AAL)
• 
  to be contd...

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• ATM Application
• ATM Services Categories
• ATM advatages
• ATM advantages
• ATM challenges
• References

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ATM-Definition

• Asynchronous Transfer Mode (ATM) is a technology
  that has the potential of revolutionizing data
  communications and telecommunications.
• ATM is a packet switching.

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What is it really?

• Low-level network layer
• Single transport mechanism
• Streamlined protocol

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ATM Standard

• ITU-T I.361
• Defines the ATM Layer functions.
• ITU-T I.363
• Defines the ATM Adaptation Layer-
• protocols.
• ITU-T I.610
• Defines the ATM Operation and
  Maintenance (OAM) functions

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The ATM network
1) User-to-Network Interface (UNI) 2)
Network-to-Network Interface (NNI) 3)
Inter-Carrier Interface (ICI)
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ATM Interfaces

• 1. User-to-Network Interface (UNI)
• Exists between a single end user and a
  public ATM network.
• 2. Network-to-Network Interface (NNI)
• Exists between switches in a single
  public ATM network.
• 3. Inter-Carrier Interface (ICI)
• It is located between two public ATM
  networks

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Important parameters

• Virtual channel
• A channel that provides transportation of ATM
  cells between two or more endpoints for
  information transfer.
• Virtual paths
• It is a group of Virtual Channels that are
  carried on the same physical facility and share
  the same Virtual Path Identifier (VPI) value.

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ATM cells

• Small size, may reduce queuing delay of high
  priority cells
• Fixed size, more efficient switching

Diagram of the NNI ATM Cell
Diagram of the UNI ATM Cell
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ATM cell content

• 1) 5 bytes header
• (I) General flow control
• defined across the UNI
• flow across the UNI
• intended to control the traffic
• 4 bits must be set to 0's.
• (II) Virtual path control
• routing field for network
• an 8-bit field for the UNI and a 12-bit
  field for the NNI, is used to identify virtual
  paths.

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Continue.

• Virtual Channel Identifier (VCI)
• 16-bit field is used to identify a virtual
  channel
• For idle cells, the VCI is set to all 0's.
• Payload Type Identifier (PTI)
• three bits of the PTI

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• Cell Loss Priority (CLP)
• The 1-bit CLP field
• used for explicit indication of the priority of
  the cell
• Header Error Control (HEC)
• 8-bit fieldIt capable of detecting all single-bit
  errors and some multiple-bit errors.

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ATM Applications
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ATM Service Categories

• Real-time services
• Constant bit rate uncompressed audio/video info
• Videoconferencing, TV, pay-per-view, VOD, etc.
• Non-real-time services
• Available bit rate bursty apps requiring
  reliable end-to-end connection
• e.g. LAN, router-to-router reliability

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ATM Advantages

• Universality
• Mixed traffic types, real-time and non-real-
  time
• Scalability
• LANs, WANs, WLANs
• Efficient use of network resources Bandwidth on
  demand concept
• Simplified network infrastructure

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ATM challenges

• In-network mux/buffering can lead to cell delay
  or loss
• Many types of traffic
• Large geographic distribution

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References

• http//www.iec.org
• Amos E. Joel, Jr., Asynchronous Transfer Mode
  (IEEE Press, 1993)
• "Broadband ISDN and ATM". http//world-class-prog
  ramme.com

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THANK YOU