D-Link DSL-2540T, User Manual

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DSL-2540T ADSL Router User Guide
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packets to pass through the Router. This enables the Router to function as
a bridge. Check this feature and enter the required information in the
ServerIP/Name, Route Target, Route Mask, PPTP Account, PPTP
Password, and MPPE Encryption fields.
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 – 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.
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).
CDVT
Cell Delay Variation Tolerance – CDVT is a measure of the cell clumping
phenomenon by which cells are delayed in the network and are
clumped together and arrive at a system at a faster rate than negotiated.
Increasing the CDVT creates greater bucket depth.
MBS
Maximum Burst Size – The MBS is the maximum number of bytes that can
be sent continuously from the source to the destination dropping any
packets. Some ATM providers set the MBS and CDVT very low and adjust
up if problems occur.