Low-Latency Priority Queuing - Cisco 10000 Series Configuration Manual

Prioritizing Services
Voice, video, and data applications have differing quality of service needs. Voice applications, for
example, require a small but guaranteed amount of bandwidth, are less tolerant of packet delay or loss,
and require low jitter. A data application such as File Transfer Protocol (FTP) needs more bandwidth
than voice and can tolerate packet delay and jitter. To provide end-to-end differentiated services, QoS
policies must allow critical applications to receive the resources required while ensuring that other
applications are not neglected.
Priority queuing offers the ability to deliver assured bandwidth, low latency, low jitter, and low packet
loss for voice applications while simultaneously ensuring that other applications receive portions of the
available bandwidth.
This chapter describes low-latency priority queuing and includes the following topics:
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Low-Latency Priority Queuing

Using a single queue for packets from all traffic streams is simple, efficient, and offers optimal average
delay per packet because the queue uses the entire link bandwidth to transmit waiting packets. The
drawback to this method is it does not distinguish among different traffic streams—voice, data, video.
The more traffic in a stream, the larger its share of the link bandwidth. Packets arriving first are the first
packets out of the queue, regardless of the packet type.
OL-7433-09
Low-Latency Priority Queuing, page 8-1
Multi-Level Priority Queues, page 8-3
Child Service Policy Allowed Under Priority Class, page 8-4
Interfaces Supporting Priority Queuing, page 8-4
Queues per Policy Map, page 8-5
Restrictions and Limitations for Priority Queuing, page 8-5
Restrictions for Multi-Level Priority Queues, page 8-5
Configuring a Priority Queue, page 8-6
Configuring Multi-Level Priority Queues, page 8-7
Configuration Examples for Configuring Priority Queues, page 8-9
Verifying and Monitoring Priority Queues, page 8-11
Verification Examples for Priority Queues, page 8-11
Related Documentation, page 8-13
C H A P T E R
Cisco 10000 Series Router Quality of Service Configuration Guide
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8-1