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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
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.
PCR
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.
SCR
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).
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