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T1/E1 Digital Voice Port Adapter Installation and Configuration
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Chapter 4 Configuring the PA-VXA, PA-VXB, and PA-VXC
Configuring Voice over IP
Under most circumstances, the default voice-port command values are adequate to configure FXO and
FXS ports to transport voice data over your existing IP network. Because of the inherent complexities
involved with PBX networks, E&M ports might need specific voice-port values configured, depending
on the specifications of the devices in your telephony network. For information about configuring voice
ports, see the
“Configure Voice Ports” section on page 4-22
.
Configure IP Networks for Real-Time Voice Traffic
You need to have a well-engineered end-to-end network when you run delay-sensitive applications such
as VoIP. Fine-tuning your network to adequately support VoIP involves a series of protocols and features
geared toward quality of service (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 must consider 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
the Cisco 7200 series routers, Cisco 7200 VXR routers, Cisco 7401ASR routers, or Cisco 7500 series
routers 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 take into consideration the functions of both edge and backbone
routers in your network, and then select the appropriate QoS tool or tools.
In general, edge routers perform the following QoS functions:
•
Packet classification
•
Admission control
•
Bandwidth management
•
Queuing
In general, backbone routers perform the following QoS functions:
•
High-speed switching and transport
•
Congestion management
•
Queue management
Scalable QoS solutions require cooperative edge and backbone functions.
Although not mandatory, some QoS tools have been identified as valuable in fine-tuning your network
to support real-time voice traffic. To configure your IP network for QoS using these tools, perform one
or more of the following tasks:
•
Configure RSVP for Voice, page 4-10
•
Configure Multilink PPP with Interleaving, page 4-11
•
Configure RTP Header Compression, page 4-12
•
Configure Custom Queuing, page 4-14
•
Configure Weighted Fair Queuing, page 4-14
Each of these tasks is discussed in the following sections.
