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Configuring Voice-over-IP

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Cisco IOS software provides many other tools for ensuring QoS, such as custom queuing, priority

queuing, and weighted fair queuing. For further information and more detailed examples of QoS

configuration, refer to the Cisco 1751 Router Software Configuration Guide.

QoS measures the level of network performance. It does not directly measure the quality of the voice

Note

signal.

Configuring VoIP on a Frame Relay link involves special considerations. These are discussed in the

section

Need for Quality of Service

On a relatively low-bandwidth connection, such as a PPP or High-Level Data Link Control (HDLC)

serial link, you should consider using methods to ensure QoS. If you have a high-bandwidth network,

such as Ethernet or Fast Ethernet, and voice and data traffic together occupy only a small fraction of the

bandwidth available, you might not need to provide QoS. (See

Figure 21

IP Precedence

Use the ip precedence command to give voice packets a higher priority over other IP data traffic. Every

IP packet is given a precedence level. In IP precedence, the numbers 1 through 5 identify classes for IP

flows; the numbers 6 through 7 are used for network and backbone routing and updates. You can

configure voice packets for higher priority by setting the IP precedence value to 5. Internal routers using

weighted fair queuing will give these packets priority. This command only applies to VoIP dial peers.

The following example sets the IP precedence to 5:

Router> enable

Password:

Router# configure terminal

Router(config)# dial-peer voice 221 voip

Router(config-dial-peer)# ip precedence 5

The ip precedence command should also be used if RSVP is not enabled and the user would like to give

voice packets a higher priority over other IP data traffic.

Cisco 1751 Voice-over-IP Quick Start Guide

Multilink Point-to Point Protocol (PPP) interleaving

Real-Time Transport Protocol (RTP) header compression

"Configuring Frame Relay for

Bandwidth v. Quality of Service

Low bandwidth

needs QoS

High bandwidth

might not need QoS

VoIP."

Figure

21.)

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