Cisco CISCO1751 Quick Start Manual page 26

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
26
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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