VBR

Communications Systems Glossary

Communications Systems — Switching — Asynchronous Transfer Mode — VBR

 

 

 

 

 

 

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Information on VBR

VBR is a service class for asynchronous transfer mode networks (ATM networks) in which the cell rate is allowed to vary in accordance with the connection contract. In VBR systems the output bit rate varies (as opposed to constant bit rate, in which it does not). Variable rates are produced from codecs for voice and video (MPEG2) due to the compression method employed, whose output depends on the redundancy in the original data. A codec may buffer its output and add padding bits to convert the variable bit rate to match the constant bit rate requirements of the channel. In ATM systems, the VBR method of flow control allocates bandwidth to a call when it is first set up (as in CBR) but the rate is allowed to increase for short periods if the bandwidth is available.


Other topics in our resources on Communications Systems related to VBR include: 
 
  • Available bit rate (ABR)
  • constant bit rate (CBR)
  • unconstrained bit rate (UBR)
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  • Broadband integrated services digital network (BISDN)
  • Cell relay
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  • Cell
  • Virtual circuit (VC)
  • ATM adaptation layer (AAL)

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