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Configuring Voice over IP
The information in this chapter applies to configuration of Voice over IP (VoIP) on the Cisco VGD 1T3
voice gateway.
VoIP technology enables voice-capable routers and switches to transport packetized live voice traffic
such as telephone calls over IP data intranetworks or internetworks rather than public switched telephone
networks (PSTN) or private TDM (PBX) networks. VoIP thus enables toll bypass, remote PBX presence
over WANs, unified voice and data trunking, and plain old telephone service (POTS)-Internet telephony
gateways. VoIP enables more efficient and full use of your existing IP data network, both reducing
transmission costs and possibly your need to support dual (voice and data) networks.
Routers and switches such as the Cisco VGD 1T3 voice gateways can handle origination, transport, and
termination of VoIP traffic. They digitize analog voice signals, compress them, package them into a
series of discrete packets, and transport them interleaved with data packets. They can transmit VoIP
packets to both VoIP and non-VoIP destinations, and can receive both VoIP and nonVoIP calls. When
data lines are busy, they can spill traffic onto the PSTN.
To ensure acceptable quality of service (QoS) for your voice users, it is important that you configure
your gateway carefully and monitor its performance vigilantly—to ensure, for voice traffic, priority
service with minimal loss and delay. Unlike most other types of data, voice is intolerant of almost any
form of loss or delay. Users cannot wait for a destination device to reorder packets and request that the
sending device retransmit any that are missing, as it does for most other data types.
To configure basic VoIP, in general you need to do the following:
•
Configure signaling on voice ports
•
Configure dial peers
You might also need to do the following:
•
Configure voice QoS features
•
Configure Frame Relay for VoIP
•
Configure the gateway to distinguish between voice and modem calls (necessary when the
network-access server supports both modem dialup and VoIP users on the same POTS interface)
•
Optimize dial-peer and network-interface configurations
•
Configure VoIP for Microsoft NetMeeting