Specifications

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Cisco 1751 Router Software Configuration Guide
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– Make routing and dialing transparent to the user—for example, avoid secondary dial tones
from secondary switches, where possible.
– Contact your PBX vendor for instructions about how to reconfigure the appropriate PBX
interfaces.
After you have analyzed your dial plan and decided how to integrate it into your existing IP network,
you are ready to configure your network devices to support VoIP.
Configuration Tasks
To configure VoIP on your router, you need to perform the following steps:
Step 1 Configure your IP network to support real-time voice traffic. Refer to the following section for
information about selecting and configuring the appropriate QoS tool or tools to optimize voice traffic
on your network.
Step 2 (Optional) If you plan to run VoIP over Frame Relay, you need to consider certain factors so that VoIP
runs smoothly. For example, a public Frame Relay cloud provides no guarantees for QoS. Refer to the
“Configure Frame Relay for VoIP” section on page xxiv for information about deploying VoIP over
Frame Relay.
Step 3 Use the num-exp command to configure number expansion if your telephone network is configured so
that you can reach a destination by dialing only a portion (an extension number) of the full E.164
telephone number. Refer to the “Configure Number Expansion” section on page viii for information
about number expansion.
Step 4 Use the dial-peer voice command to define dial peers and switch to the dial-peer configuration mode.
Refer to the “Configure Dial Peers” section on page ix and the “Additional VoIP Dial Peer
Configurations” section on page xxi for additional information about configuring dial peers and
dial-peer characteristics.
Step 5 Configure your router to support voice ports. Refer to the “Configure Voice Ports” section on page xiv
for information about configuring voice ports.
Configure IP Networks for Real-Time Voice Traffic
You need to have a well-engineered, end-to-end network when running delay-sensitive applications
such as VoIP. Fine-tuning your network to adequately support VoIP involves a series of protocols and
features to improve QoS. It is beyond the scope of this document to explain the specific details relating
to wide-scale QoS deployment. Cisco IOS software provides many tools for enabling QoS on your
backbone, such as Random Early Detection (RED), Weighted Random Early Detection (WRED), Fancy
Queuing (meaning custom, priority, or weighted fair queuing), and IP precedence. To configure your IP
network for real-time voice traffic, you need to take into consideration the entire scope of your network
and then select the appropriate QoS tool or tools.
The important thing to remember is that QoS must be configured throughout your network—not just on
your router running VoIP—to improve voice network performance. Not all QoS techniques are
appropriate for all network routers. Edge routers and backbone routers in your network do not
necessarily perform the same operations; the QoS tasks they perform might differ as well. To configure
your IP network for real-time voice traffic, you need to consider the functions of both edge and
backbone routers in your network and then select the appropriate QoS tool or tools.