Cisco 1751 Installation Guide download pdf (Page 16)

Cisco 1751 Voice-over-IP Quick Start Guide

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Configuring Voice-over-IP

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

Table 6 lists telephone numbers and voice ports for the West router. (For information about port

numbering, refer to the section on “Determining Voice Port Numbering” earlier in this guide.)

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 2

–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.

You should construct a table similar to Table 7 for your own routers, assigning your own telephone

numbers and dial-peer tags.

Table 6 West Router Telephone Numbers and Voice Ports

Telephone Number Voice Port

408 555-3737 0/0

408 555-4141 0/1

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

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 33 34

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