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Chapter 4: Dial Plans and Dial Peers

Cisco Press

By Cheryl Schmidt and Ernie Friend, Network World
April 27, 2007 01:10 PM ET

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A dial plan allows people to call each other by dialing a number on the telephone. Dial plans include access codes, area codes, and specialized codes. The North American Public Switched Telephone Network (PSTN) uses a ten-digit dial plan that includes a three-digit area code and a seven-digit telephone number (that is, 904-555-4568). Most private branch exchanges (PBXs) support variable-length dial plans that use 3 to 11 digits. Dial plans must comply with the telephone networks to which they connect. Dial plans are similar to IP addressing in that only totally private voice networks that are not linked to the PSTN or to other PBXs can use any dial plan they choose.

Dial peers are used to configure dial plans and to identify call source and destination endpoints. They also define each call leg in the call connection. Dial peers are a critical component of VoIP.

Types of Dial Peers

The first basic command required to configure dial peers is dial-peer. The two types of dial peers used in these labs are Plain Old Telephone System (POTS) and voice over IP (VoIP) dial peers. Other dial peer options are multimedia over IP (MMoIP), voice over ATM (VoATM), and voice over Frame Relay (VoFR). The following examples show basic configurations for POTS and VoIP dial peers:

dial-peer voice 3 pots
 destination-pattern 5556123
 port 2/0/1

dial-peer voice 4 voip
 destination-pattern 5557000
 session target ipv4:12.91.0.1

The POTS dial peer maps a dial string to a voice port on a local router or gateway. A dial peer is configured using the dial-peer voice tag {pots | vofr | voip} command. The tag is a number between 1 and 2147483647 that identifies an individual dial peer. POTS dial peers are configured using the dial-peer voice tag pots command, and VoIP dial peers are configured using the dial-peer voice tag voip command. In most cases, POTS dial peers are used to connect a physical voice port to a PBX, a telephone, or the PSTN. VoIP a dial peers are used to define packet voice network attributes and map dial strings to a remote router or device. The following sample configurations provide basic examples of POTS and VoIP dial peers. The first example is a POTS dial peer, and the second is a VoIP dial peer.

dial-peer voice 3 pots <--POTS dial peer
 destination-pattern 5556123
 port 2/0/1

dial-peer voice 4 voip <--VoIP dial peer
 destination-pattern 5557000
 session target ipv4:12.91.0.1

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