Configuration Tasks
12
Cisco IOS Release 12.0(7)T
Configuring Dial Peers
The key point to understanding how VoIP functions is to understand dial peers. Each dial peer
defines the characteristics associated with a call leg, as shown in Figure 3 and Figure 4. A call leg is
a discrete segment of a call connection that lies between two points in the connection. All of the call
legs for a particular connection have the same connection ID.
There are two different kinds of dial peers:
• POTS—Dial peer describing the characteristics of a traditional telephony network connection.
POTS peers point to a particular voice port on a voice network device.
• VoIP—Dial peer describing the characteristics of a packet network connection. VoIP peers point
to specific VoIP devices.
An end-to-end call comprises four call legs, two from the perspective of the source access server as
shown in Figure 3, and two from the perspective of the destination access server as shown in
Figure 4. A dial peer is associated with each call leg. Dial peers are used to apply attributes to call
legs and to identify call origin and destination. Attributes applied to a call leg include QoS, codec,
VAD, and fax rate.
Figure 3 Dial Peer Call Legs from the Perspective of the Source Router
Figure 4 Dial Peer Call Legs from the Perspective of the Destination Router
Inbound versus Outbound Dial Peers
Dial peers are used for both inbound and outbound call legs. It is important to remember that these
terms are defined from the access server’s perspective. An inbound call leg originates outside the
access server. An outbound call leg originates from the access server.
For inbound call legs, a dial peer might be associated to the calling number or the port designation.
Outbound call legs always have a dial peer associated with them. The destination pattern is used to
identify the outbound dial peer. The call is associated with the outbound dial peer at setup time.
10353
IP cloud
Destination
Source
Call leg for POTS
dial peer 1
Source router
Call leg for VoIP
dial peer 2
10354
IP cloud
Destination router
Call leg for POTS
dial peer 4
Call leg for VoIP
dial peer 3
Destination
Source
