ZyXEL Communications P-660N-T1A, User Manual

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Chapter 6 WAN Setup
P-660N-T1A User’s Guide
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The VBR-RT (real-time Variable Bit Rate) type is used with bursty connections that
require closely controlled delay and delay variation. It also provides a fixed
amount of bandwidth (a PCR is specified) but is only available when data is being
sent. An example of an VBR-RT connection would be video conferencing. Video
conferencing requires real-time data transfers and the bandwidth requirement
varies in proportion to the video image's changing dynamics.
The VBR-nRT (non real-time Variable Bit Rate) type is used with bursty
connections that do not require closely controlled delay and delay variation. It is
commonly used for "bursty" traffic typical on LANs. PCR and MBS define the burst
levels, SCR defines the minimum level. An example of an VBR-nRT connection
would be non-time sensitive data file transfers.
Unspecified Bit Rate (UBR)
The Unspecified Bit Rate (UBR) ATM traffic class is for bursty data transfers.
However, UBR doesn't guarantee any bandwidth and only delivers traffic when the
network has spare bandwidth. An example application is background file transfer.