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P-660 series Support Notes
14. What do the parameters (PCR, SCR, MBS) mean?
Traffic shaping parameters (PCR, SCR, MBS) can be set in Menu 4 and Menu 11.6
and is valid for both incoming and outgoing direction since G.shdsl is symmetric.
Peak Cell Rate(PCR): The maximum bandwidth allocated to this connection. The
VC connection throughput is limited by PCR.
Sustainable Cell Rate(SCR): The least guaranteed bandwidth of a VC. When there
are multi-VCs on the same line, the VC throughput is guaranteed by SCR.
Maximum Burst Size(MBS): The amount of cells transmitted through this VC at
the Peak Cell Rate before yielding to other VCs. Total bandwidth of the line is
dedicated to single VC if there is only one VC on the line. However, as the other VC
asking the bandwidth, the MBS defines the maximum number of cells transmitted via
this VC with Peak Cell rate before yielding to other VCs.
The P-660 holds the parameters for shaping the traffic among its virtual channels. If
you do not need traffic shaping, please set SCR = 0, MBS = 0 and PCR as the
maximum value according to the line rate (for example, 2.3 Mbps line rate will result
PCR as 5424 cell/sec.)
15.Why do we perform traffic shaping in the P-660 ?
The P-660 must manage traffic fairly and provide bandwidth allocation for different
sorts of applications, such as voice, video, and data. All applications have their own
natural bit rate. Large data transactions have a fluctuating natural bit rate. The P-660
is able to support variable traffic among different virtual connections. Certain traffic
may be discarded if the virtual connection experiences congestion. Traffic shaping
defines a set of actions taken by the P-660 to avoid congestion; traffic shaping takes
measures to adapt to unpredictable fluctuations in traffic flows and other problems
among virtual connections.
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All contents copyright © 2005 ZyXEL Communications Corporation.
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