Cisco Systems CISCO1751 quick start Local Dial Peers, Telephone Number, Voice Port, Dial-Peer Tag

Configuring Voice-over-IP

Note You can name your router by using the global configuration hostname command.

(For information about port numbering, refer to the section on “Determining Voice Port Numbering” earlier in this guide.)

Table 6 West Router Telephone Numbers and Voice Ports

Telephone Number	Voice Port
408 555-3737	0/0
408 555-4141	0/1

Note If your router is configured with three VICs, a total of six telephones and fax machines can be connected to it. As the router has only three slots, you need to replace one VIC with a WIC to provide an interface for IP connectivity to the WAN and for data traffic. To accommodate more than six voice devices, you need to add more routers or use an E&M VIC and a local PBX, rather than connecting every telephone to its own FXS VIC.

Local Dial Peers

To route a received voice call to the right destination, the router needs to know which telephone number belongs to each voice port. For instance, if a call comes in for 408 555-3737, the router needs to know that this telephone is connected to voice port 0/0 (as shown in Figure 11.) In other words, the router needs to know the information in Table 6.

To hold this information, Cisco IOS software uses objects called dial peers. A telephone number, a voice port, and other call parameters are tied together by associating them all with the same dial peer. Configuring dial peers is similar to configuring static IP routes—you are telling the router what path to follow to route the call. All voice technologies use dial peers to define the characteristics associated with a call leg. A call leg is a segment of a call path, for instance, between a telephone and a router, a router and a network, a router and a PBX, or a router and the PSTN. Each call leg corresponds to a dial peer.

Dial peers are identified by numbers, but they are usually referred to as tags to avoid confusion with telephone numbers. Dial-peer tags are arbitrary integers that can range from 1 to 231–1(2147483647). Within the allowed range, you can choose any dial-peer tag that is convenient or makes sense to you. Dial peers on the same router must have unique tags, but you can reuse the tags on other routers.

Table 7 assigns a dial-peer tag to each telephone number and its associated voice port on the West router. This type of dial peer is called a POTS dial peer or a local dial peer. The term “POTS” (plain old telephone service) means that the dial peer associates a physical voice port with a local telephone device.

Table 7	West Router Local Dial Peers
Telephone Number		Voice Port	Dial-Peer Tag
408 555-3737		0/0	401
408 555-4141		0/1	402

You should construct a table similar to Table 7 for your own routers, assigning your own telephone numbers and dial-peer tags.

Cisco 1751 Voice-over-IP Quick Start Guide

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