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Cisco 1751 Voice-over-IP Quick Start Guide
78-11259-05
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.)
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 peer
s. 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
31
–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
