Asynchronous Transfer Mode ATM

1
Asynchronous Transfer Mode - ATM
2
ATM - 1

• ATM provides support for B-ISDN
• High speed switch , circuit oriented micro
  controlled hardware
• Data rates 100 to 600M, typical 155M
• Multiple inputs and outputs, typically 8 by 8,
  cost 20K

3
ATM - 2

• Support for virtual path and channel
• ATM cell structure
• Header Data
• 5 octets 48 octets octetbyte
• Traffic loading and distribution diagram
• BW reduced by heavy localised traffic

4
ATM 3

• Graph delay vs loading
• Switches have data buffers various schemes,
  both input and output
• Burstiness is a problem
• Prioritisation on channels, lost cell may be
  tolerated
• Sychronous vs Asynchronous

5
ATM - 4

• Diagram of ATM switch connecting MANs
• Telecommunications managed network TMN
• - switches setup remotely
• - dynamic setup possible
• - bi-directional data transfer
• - switch state data transfer

6
ATM 5

• Modes of data transfer
• CBR - constant bit rate
• VBR variable bit rate
• ABR - available bit rate
• Useful link
• http//osiris.sunderland.ac.uk/cs0jti/elc301/bt-t
  ech/start.htm

7
ATM - 6

• CBR
• Advantage guaranteed bandwidth for video
  conferencing
• Bandwidth may not be required at all times
• Disadvantage costs are higher than other modes

8
ATM - 7

• ABR
• Various user share bandwidth
• Advantage costs are lower
• Disadvantage some data maybe lost when traffic
  levels are high
• ABR user a feedback loop to control the loss of
  cells

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ATM - 7

• Bandwidth 155 Mbps
• CBR traffic 51 Mbps
• VBR 100Mbps
• AAL ATM Adaption Layer
• Converts data source into ATM traffic type

10
ATM - 8

• Link to notes
• http//osiris.sunderland.ac.uk/cs0jti/mic210/webs
  ite/lecs/
• BT technology
• http//osiris.sunderland.ac.uk/cs0jti/elc301/bt-t
  ech/start.htm