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T1/E1 Digital Voice Port Adapter Installation and Configuration
OL-3592-02
Chapter 4 Configuring the PA-VXA, PA-VXB, and PA-VXC
Configuring Voice over IP
Direct Inward Dial for POTS Peers
Direct inward dial (DID) is used to determine how the called number is treated for incoming POTS call
legs. As shown in
, incoming means from the perspective of the router. In this case, it is the
call leg coming into the router to be forwarded through to the appropriate destination pattern.
Figure 4-7
Incoming and Outgoing POTS Call Legs
Unless otherwise configured, when a call arrives on the router, the router presents a dial tone to the caller
and collects digits until it can identify the destination dial peer. After the dial peer has been identified,
the call is forwarded through the next call leg to the destination.
There are cases when it might be necessary for the router to use the called number Dialed Number
Identification Service (DNIS) to find a dial peer for the outgoing call leg—for example, if the switch
connecting the call to the router has already collected the digits. DID enables the router to match the
called number with a dial peer and then directly place the outbound call. With DID, the router does not
present a dial tone to the caller and does not collect digits; it forwards the call directly to the configured
destination.
To use DID and an incoming called number, a dial peer must be associated with the incoming call leg.
It is helpful to understand the logic behind the algorithm used to associate the incoming call leg with the
dial peer.
The algorithm used to associate incoming call legs with dial peers uses three inputs (which are derived
from signaling and interface information associated with the call) and four defined dial peer elements.
The three signaling inputs are:
•
Called number (DNIS)—Set of numbers representing the destination, which is derived from the
ISDN setup message or CAS DNIS.
•
Calling number (ANI)—Set of numbers representing the origin, which is derived from the ISDN
setup message or CAS DNIS.
•
Voice port—Voice port carrying the call.
The four defined dial peer elements are:
•
Destination pattern—Pattern representing the phone numbers to which the peer can connect.
•
Answer address—Pattern representing the phone numbers from which the peer can connect.
•
Incoming called number—Pattern representing the phone numbers that associate an incoming call
leg to a peer based on the called number or DNIS.
•
Port—Port through which calls to this peer are placed.
PBX
Router A
Incoming
call leg
Outgoing
call leg
PBX
26560
IP
cloud
72xx
Router B
72xx
