Configuring Voice-over-IP
Dial Plan
Use a dial plan to map the destination telephone numbers with the voice ports on the router. In North America, the North American Numbering Plan (NANP) is used, which consists of an area code, an office code, and a station code. Area codes are assigned geographically, office codes are assigned to specific switches, and station codes identify a specific port on that switch. The format in North America is 1Nxx-Nxx-xxxx, with N = digits 2 through 9 and x = digits 0 through 9. Internationally, each country is assigned a one- to three-digit country code; the country’s dialing plan follows the country code.
In corporate environments, VoIP can be configured to recognize extension numbers and expand them into their full E.164 dialed number by using two commands in tandem: destination-patternand num-exp. Before you configure these two commands, map individual telephone extensions with their full E.164 dialed numbers. This can be done easily by creating a number expansion table.
For Cisco voice implementations, two types of dial peers are used to match a dialed number to either a local telephony port or a remote IP address:
•POTS dial peer associates a physical voice port with a local telephone device, and the key commands you need to configure are the port and destination-patterncommands as shown in the following example:
West(config)# dial-peer voice 401 pots
West(config-dial-peer)#destination-pattern 14085553737
West(config-dial-peer)# port 0/0
The destination-patterncommand defines the telephone number associated with the POTS dial peer. The port command associates the POTS dial peer with a specific logical dial interface, normally the voice port connecting your router to the local POTS network.
•VoIP dial peer associates a telephone number with an IP address, and the key commands you need to configure are the destination-patternand session target commands as shown in the following example:
West(config)# dial-peer voice 501 voip
West(config-dial-peer)#destination-pattern 1919555....
West(config-dial-peer)#session target ipv4:192.168.11.3
The destination-patterncommand defines the telephone number associated with the VoIP dial peer. The session target command specifies a destination IP address for the VoIP dial peer.
Use the dial-peer voice command to define dial peers and change to dial peer configuration mode. To see an example, refer to the individual sections on configuring FXS, FXO, and E&M interfaces later in this guide.
Wildcards and Number Expansion
Office PBXs are configured so that a user can dial a local call (within the same PBX) by dialing the extension only—for instance, the four-digit extension 3737 or the five-digit extension 53737 instead of the full telephone number, 1 408 555-3737.
You can provide the same shortcut on a VoIP network by using the number-expansion(num-exp) command.
East(config)# num-exp 5.... | 1408555.... |
This command tells the router to expand a particular sequence of dialed numbers into a complete telephone number (destination pattern) as shown in Table 5.
Cisco 1751 Voice-over-IP Quick Start Guide
