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ISDN Features
Primary Rate Interface (PRI), Answering Calls
12 ◆ Aspire ISDN PRI Manual
How the Telco Handles PRI Trunks
In many cases, the telco will route an incoming PRI call to any of the available 23 circuits on the PRI PCB.
This makes it difficult to determine the type of call by the trunk that is ringing. It also prevents using Direct
Inward Lines to route incoming calls, since any call sent to the PRI PCB can appear on any circuit. During
programming, set up all trunks on the same PRI PCB in the same way. Refer to Programming below.
To provide more precise routing of PRI trunks, set up PRI Direct Inward Dialing (DID). With DID, the sys-
tem uses the last three or four digits of the Called Number Information Element to route an incoming call via
the system’s DID translation tables. When programming PRI trunks for DID, refer to the Aspire Software
Manual (P/N 0893200) for additional DID programming.
In addition, in areas where ISDN is not uniformly implemented, many ISDN calls may route to the 3.1 Khz Audio
Ring Group. This can occur if the telco automatically designates a call as 3.1 KHz when it is from a non-ISDN
telephone. To provide uniform treatment of incoming PRI calls, consider having the Ring Group assignments for
both normal PRI calls and 3.1KHz Audio calls. Refer to Programming below for more information.
How the Telephone System Handles PRI Trunks
The Channel ID of an incoming SETUP message on a PRI line is related to the trunk group number. The system
will create the trunk line number as the lowest trunk port number in the range of the same trunk group related to
the channel number of the Channel ID information element of an incoming call’s SETUP message.
For example, referring to the chart below, the system translates the call as being trunk port 4.
Conditions
● PRI requires the installation of a T-Serve II CSU (P/N 85950) or Quad Datasmart DSU (P/N 85956).
Consult your sales representative for more information.
Default Setting
● Once set, PRI trunks ring extension 301 and flash at all other extensions just like other trunk calls.
Trunk
Number
Trunk
Group
Channel
Number
111
212
313
424
525
626<--- Incoming Call
727
858
. . . 23 . . . 5 . . . 23
All 23 circuits on the PRI PCB must be identically programmed
since any call sent to the PRI PCB can appear on any circuit.