Cisco 10000 Series User Manual

5-14
Cisco 10000 Series Router Quality of Service Configuration Guide
OL-7433-09
Chapter 5 Distributing Bandwidth Between Queues
Distribution of Remaining Bandwidth Using Ratio
Distribution of Remaining Bandwidth Using Ratio
The Distribution of Remaining Bandwidth Using Ratio feature allows service providers to prioritize
subscriber traffic during periods of congestion. A bandwidth-remaining ratio is used to influence how
the router allocates excess bandwidth (unused by priority traffic) to a class of non-priority traffic. Instead
of using only bandwidth rate, the router considers configured minimum bandwidth rates, maximum
bandwidth rates, and bandwidth-remaining ratios when determining excess bandwidth allocation. A
bandwidth-remaining ratio adds more flexibility in prioritizing traffic and enables you to influence
excess bandwidth allocation by basing the bandwidth-remaining ratio on factors other than speed.
When bandwidth-remaining ratios are not specified, the hierarchical queuing framework (HQF)
scheduler on the PRE3 does the following:
• Computes a default bandwidth-remaining ratio based on the subinterface speed—ATM interfaces
• Uses the minimum bandwidth-remaining ratio allowed (currently 1 on the PRE3)—Other interfaces
such as VLANs and Frame Relay DLCIs
With bandwidth-remaining ratios, service providers have more flexibility in assigning priority to
subinterfaces and queues during congestion. In addition to speed, you can base the bandwidth-remaining
ratio on alternative factors, such as a service product or subscription rate. In this way, for example, you
can give higher weight to subinterfaces carrying business services and lower weight to subinterfaces
carrying residential services. The bandwidth-remaining ratio enables the HQF scheduler to service a
subinterface with a low SCR but a high bandwidth-remaining ratio more frequently than servicing a
subinterface with a high SCR but a low bandwidth-remaining ratio.
The Distribution of Remaining Bandwidth Using Ratio feature is available on outbound interfaces only.
Feature History for Bandwidth-Remaining Ratios
Bandwidth-Remaining Ratio
A bandwidth-remaining ratio is a value from 1 to 1000 that is used to determine the amount of unused
(excess) bandwidth to allocate to a class queue or subinterface-level queue during congestion. The router
allocates excess bandwidth relative to the other class queues and subinterface-level queues configured
on the physical interface. The bandwidth-remaining ratio value does not indicate a percentage. For
example, a subinterface with a bandwidth-remaining ratio of 100 receives 10 times the unused (excess)
bandwidth during congestion than a subinterface with a bandwidth-remaining ratio of 10.
Without bandwidth-remaining ratios, the router allocates excess bandwidth based on the following:
• Speed of the subinterface (for example, the configured SCR)—ATM subinterfaces
• Minimum bandwidth-remaining ratio allowed (currently 1 on the PRE3)—Interface types such as
VLANs and Frame Relay DLCIs
With bandwidth-remaining ratios, excess bandwidth allocation can be based on factors other than the
bandwidth rate (for example, service product or subscription rate).
Cisco IOS Release Modification
Release 12.2(31)SB22 This feature was introduced and implemented on the Cisco 10000 series
router for the PRE3.

Cisco 10000 Series Specifications

General

Brand	Cisco
Model	10000 Series
Category	Network Router
Language	English