Cisco 10000 Series User Manual

5-3
Cisco 10000 Series Router Quality of Service Configuration Guide
OL-7433-09
Chapter 5 Distributing Bandwidth Between Queues
Bandwidth Distribution Between Queues
Note The router only supports the bandwidth command on outbound interfaces.
Interfaces Not Supporting the bandwidth Command
• ATM unshaped (no peak cell rate specified) UBR PVCs and point-to-point subinterfaces
• IP tunnel
• Virtual-access (See the “VAI QoS Inheritance” section on page 4-24.)
Note The router does not support the bandwidth command on inbound interfaces.
Unused Bandwidth Allocation
After the Cisco 10000 series router allocates bandwidth to priority and bandwidth guaranteed class
queues, the router divides unused (excess) bandwidth among the packets remaining in the class queues.
• For all releases prior to Cisco IOS Release 12.0(19)SL, the router divides the unused bandwidth
equally among the class queues with outstanding packets.
• For Cisco IOS Release 12.0(19)SL and later releases, the router divides unused bandwidth
proportional to the class bandwidth guarantee. You can override this proportional distribution by
using the bandwidth remaining percent command. The router distributes unused bandwidth only
to non-priority queues; a priority queue never receives more than its guaranteed bandwidth.
In Example 5-1, the policy-map named VLAN guarantees 30 percent of the bandwidth to the class
named Customer1 and 60 percent of the bandwidth to the class named Customer2. If you apply the
VLAN policy map to a 1-Mbps link, 300 kbps is guaranteed to class Customer1 and 600
kbps is
guaranteed to class Customer2, with 100 kbps remaining for the class-default class. If the class-default
class does not need additional bandwidth, the unused 100 kbps is available for use by class Customer1
and class Customer2. If both classes need the bandwidth, they share it in proportion to the configured
rates. In this example, the sharing ratio is 30:60 or 1:2.
Example 5-1 Excess Bandwidth Allocation
Router(config)# policy-map VLAN
Router(config-pmap)# class Customer1
Router(config-pmap-c)# bandwidth percent 30
Router(config-pmap-c)# exit
Router(config-pmap)# class Customer2
Router(config-pmap-c)# bandwidth percent 60
Traffic Classes That Can Use Excess Bandwidth
The bandwidth and priority commands provide bandwidth guarantees that are often described as
bandwidth that is reserved or set aside. However, neither command implements a true reservation of
bandwidth. If a traffic class is not using its configured bandwidth, the unused bandwidth is shared among
the other classes.
The Cisco 10000 series router guarantees a priority class 95 percent of the bandwidth. As a result, the
priority class can starve other traffic classes unless you configure policing. The router does not police
the priority class unless you configure a policer.

Cisco 10000 Series Specifications

General

Brand	Cisco
Model	10000 Series
Category	Network Router
Language	English