Feature History For Vc Weighting; Determining Vc Weighting—Cisco Ios Release 12.0(17)Sl To Release 12.3(7)Xi1 - Cisco 10000 Series Configuration Manual

Chapter 15 Oversubscribing Physical and Virtual Links
Table 15-2
Cisco IOS Release
Release 12.2(28)SB and later releases
Release 12.2(31)SB2 and later releases
For information about VC weighting for a specific release, see the following sections:
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•
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Feature History for VC Weighting

Cisco IOS Release
Release 12.3(7)XI1
Release 12.2(28)SB
Release 12.2(31)SB2
Determining VC Weighting—Cisco IOS Release 12.0(17)SL to Release 12.3(7)XI1
In Cisco IOS Release 12.0(17)SL to Cisco IOS Release 12.3(7)XI1, the router determines the weight of
a particular VC in proportion to the speed of the VC. Without oversubscription, the router allocates
bandwidth to each VC, up to the VC's configured SCR. As a result, VCs with higher SCR values get
more bandwidth.
With oversubscription, the sum of the sustained cell rate (SCR) values of all of the VBR-nrt VCs is
greater than the rate of the interface. If all of an interface's VCs attempt to send cells to the segmentation
and reassembly (SAR) mechanism of the router at a rate that exceeds their SCR values, bandwidth
calculation occurs in the following ways:
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•
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OL-7433-09
VC Weighting on the Cisco 10000 Series Router
Feature History for VC Weighting, page 15-21
Determining VC Weighting—Cisco IOS Release 12.0(17)SL to Release 12.3(7)XI1, page 15-21
Determining VC Weighting—Cisco IOS Release 12.3(7)XI1 and Later Releases, page 15-22
Determining VC Weighting—Cisco IOS Release 12.2(31)SB2 and Later Releases, page 15-22
Description
The VC weighting feature was introduced on the PRE2.
This feature was integrated in Cisco IOS
Release 12.2(28)SB for the PRE2.
This feature was introduced on the PRE3.
If all of the competing VCs have the same traffic class, the router calculates bandwidth by dividing
the line rate by the number of VCs.
If the competing VCs have differing SCR values, the router either allocates the same bandwidth to
each VC or it allocates more bandwidth to VCs with a higher SCR, depending on the load at a certain
point in time. Because of this, it is difficult to predict the exact bandwidth percentage each VC has.
The SAR mechanism does not drop any cells on the router after a packet is scheduled to it. If the
rate at which VCs send cells to the SAR mechanism exceeds the SAR mechanism's capability to
transmit, the queuing system stores and subsequently drops any excess packets and the ATM
interface driver controls the rate at which it sends packets to the SAR mechanism to avoid starving
the SAR mechanism of its internal buffers.
User Configurable
Yes
Yes
Cisco 10000 Series Router Quality of Service Configuration Guide
How the Router Determines VC Weights
VC Weight
Configured using the weight
command.
Configured using the weight
command or the bandwidth
remaining ratio command
(PRE3).
Required PRE
PRE2
PRE2
PRE3
15-21