ATM Traffic Shaping, ATM Parameters Description

DSL-522T ADSL Router User Guide

ATM Traffic Shaping

The ATM settings in the WAN Settings windows for the different connection types can be used to adjust QoS parameters for ADSL clients. This may not be available to all ADSL accounts.

ATM Settings for WAN connection

Additional ATM settings for PPPoE or PPPoA connections:

ATM Parameters

Description

Service Category

PCR

SCR

The ATM settings allow the user to adjust ATM Quality of Service (QoS) or traffic parameters to suit specific traffic requirements. For applications or circumstances where packet loss or packet delay is a concern, ATM QoS can be adjusted to minimize problems. For most accounts, it will not be necessary to change these settings. Altering QoS settings can adversely affect performance of some commonly used Internet applications.

If you plan to change QoS or traffic parameters, contact your ISP or network services provider for information on what types of adjustment are available or possible for your account. Your ISP may not support the class of service you want to use.

To adjust ATM QoS parameters, select one of the Service Categories listed here and type in the PCR value in the entry field below. For the VBR service category, an additional parameter (SCR) must also be defined.

UBR – Unspecified Bit Rate, this is the default category used for general-purpose Internet traffic where normal levels of packet loss and delay are acceptable. For some applications or for multiple connection accounts, it may be desirable to specify the PCR.

CBR – Constant Bit Rate, usually used in circumstances where very low packet loss and very low Cell Delay Variable (CDV) are desirable.

VBR-nt– Real-time Variable Bit Rate. This models bursty traffic with specified peak and sustainable rates. Please note that when VBR-rt is specified, both PCR and SCR are required (by ATM standards).

VBR-nrt– Non-real-time Variable Bit Rate, usually used when network traffic is characterized by bursts of packets at variable intervals, and some moderate packet loss and delay is acceptable. This category is typically used for audio and video applications such as teleconferencing. The network must support QoS Class 2 to use VBR-nrt.

Peak Cell Rate – The PCR is inversely related to the time interval between ATM cells. It is specified for all three service categories (UBR, CBR and VBR) in Kbps.

Sustainable Cell Rate – The SCR is defined for the VBR service category. This is the rate that can be sustained for “bursty”, on-off traffic sources. It is a function of Maximum Burst Size (MBS) and the time interval (between cells).