Atm Qos; Traffic Shaping; Atm Traffic Classes; Constant Bit Rate (Cbr) - ZyXEL Communications IES-1248-51 User Manual

IES-1248-51 User's Guide

17.2 ATM QoS

ATM Quality of Service (QoS) mechanisms provide the best service on a per-flow guarantee.
ATM network infrastructure was designed to provide QoS. It uses fixed cell sizes and built-in
traffic management (see
services on the priority of the traffic flow.

17.3 Traffic Shaping

Traffic shaping is an agreement between the carrier and the subscriber to regulate the average
rate and fluctuations of data transmission over an ATM network. This agreement helps
eliminate congestion, which is important for transmission of real time data such as audio and
video connections.
Note: Traffic shaping controls outgoing (downstream) traffic, not incoming
(upstream).

17.3.1 ATM Traffic Classes

These are the basic ATM traffic classes defined by the ATM Forum Traffic Management 4.0
Specification.

17.3.1.1 Constant Bit Rate (CBR)

Constant Bit Rate (CBR) is an ATM traffic class that provides fixed bandwidth. CBR traffic is
generally time-sensitive (doesn't tolerate delay). CBR is used for connections that
continuously require a specific amount of bandwidth. Examples of connections that need CBR
would be high-resolution video and voice.

17.3.1.2 Variable Bit Rate (VBR)

The Variable Bit Rate (VBR) ATM traffic class is used with bursty connections. Connections
that use the Variable Bit Rate (VBR) traffic class can be grouped into real time (rt-VBR) or
non-real time (nrt-VBR) connections.
The rt-VBR (real-time Variable Bit Rate) type is used with bursty connections that require
closely controlled delay and delay variation. An example of an rt-VBR 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 nrt-VBR (non real-time Variable Bit Rate) type is used with bursty connections that do
not require closely controlled delay and delay variation. An example of an nrt-VBR
connection would be non-time sensitive data file transfers.
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Section 17.3 on page 130). This allows you to fine-tune the levels of
Chapter 17 xDSL Profiles Setup