Netopia 2200 series Software User's Manual page 70

You can choose UBR (Unspecified Bit Rate), CBR (Constant Bit Rate), or VBR (Variable
Bit Rate) from the pull-down menu and set the Peak Cell Rate (PCR) in the editable field.
UBR (Unspecified Bit Rate) guarantees no minimum transmission rate. Cells are
transmitted on a "best effort" basis. However, there is a cap on the maximum transmis-
sion rate for UBR VCs. In a practical situation:
• UBR VCs should be transmitted at a priority lower than CBR.
• Bandwidth should be shared equally among UBR VCs.
UBR applications are non-real-time traffic such as IP data traffic.
CBR (Constant Bit Rate) guarantees a certain transmission rate (although the appli-
cation may underutilize this bandwidth). A Peak Cell Rate (PCR) characterizes CBR. CBR
is most suited for real time applications such as real time voice / video, although it can
be used for other applications.
VBR (Variable Bit Rate) This class is characterized by:
• a Peak Cell Rate (PCR), which is a temporary burst, not a sustained rate, and
• a Sustained Cell Rate (SCR),
• a Burst Tolerance (BT), specified in terms of Maximum Burst Size (MBS). The MBS
is the maximum number of cells that can be transmitted at the peak cell rate and
should be less than, or equal to the Peak Cell Rate, which should be less than, or equal
to the line rate.
VBR has two sub-classes:
a. VBR non-real-time (VBR-nrt): Typical applications are non-real-time traffic, such as IP
data traffic. This class yields a fair amount of Cell Delay Variation (CDV).
b. VBR real time (VBR-rt): Typical applications are real-time traffic, such as compressed
voice over IP and video conferencing. This class transmits cells with a more tightly
bounded Cell Delay Variation. The applications follow CBR.
70