Feature History For Low-Latency Priority Queuing - Cisco 10000 Series Configuration Manual
Quality of service configuration guide
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Low-Latency Priority Queuing
Priority queuing overcomes the shortcomings of single queuing by allowing the router to dequeue and
transmit delay-sensitive data such as voice before it dequeues and sends packets in other queues. Using
priority queuing, delay-sensitive data receives preferential treatment over other traffic.
In all releases prior to Cisco IOS Release 12.0(25)S and Release 12.3(7)XI, low-latency priority queuing
(LL/PQ) and bandwidth reservation together enabled you to provide differentiated services (DiffServ).
Priority queuing lets you assign a guaranteed minimum bandwidth to one queue to minimize packet
delay. Bandwidth reservation divides the link bandwidth among the different traffic streams into multiple
queues, with each queue receiving its fair share of the link bandwidth divided among all non-empty
queues. By dividing the unused bandwidth among the queues with packets to send, multiple queuing has
the same average delay per packet as the single queue scheme, with the advantage of each queue
receiving its fair share of the bandwidth.
In Cisco IOS Release 12.0(25)S and Release 12.3(7)XI, and later releases, strict priority queuing
guarantees low-latency for any packet that enters a priority queue, regardless of the current congestion
level on the link. With strict priority queuing, the router gives the traffic full priority and services it at
line rate, which can cause bandwidth starvation of other traffic queues. To avoid this, use the police
command to restrict the amount of bandwidth the priority queue can use. When you specify the police
command, the router sets the committed information rate (CIR) for the priority queue to the bandwidth
you specify in the police command. The router must drop packets that exceed the committed rate.
The actual throughput of a priority queue does not exceed its configured value even if other queues on
Note
the link are empty.
For multilink PPP (MLPPP) bundling, the router restricts the priority queue bandwidth to the bandwidth
of one of the bundle members.
The router supports multilink PPP (MLPPP) for Cisco IOS Release 12.3(7)XI2 and later releases. For
Note
Cisco IOS Release 12.2(16)BX3 and Release 12.3(7)XI1, the router does not support MLPPP.
Feature History for Low-Latency Priority Queuing
Cisco IOS Release
Release 12.0(17)SL
Release 12.0(20)ST
Release 12.0(25)S
Release 12.2(16)BX
Release 12.3(7)XI1
Release 12.2(28)SB
Release 12.2(31)SB2
Cisco 10000 Series Router Quality of Service Configuration Guide
8-2
Description
The priority queuing feature was introduced on the router
to allow you to configure a bandwidth rate for a queue in
kilobits per second.
This feature was enhanced to allow you to configure a
bandwidth rate for a queue as a percentage.
This feature was modified to provide strict priority
queuing on the PRE1.
This feature was introduced on the PRE2 to allow you to
configure a bandwidth rate for a queue in kilobits per
second or as a percentage.
This feature was modified to provide strict priority
queuing 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.
Chapter 8
Prioritizing Services
Required PRE
PRE1
PRE1
PRE1
PRE2
PRE2
PRE2
PRE3
OL-7433-09
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