Nortel DMS-250 - Terminations and User Responses; Terminating to a PRI

Call control procedures 5-11
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
B-channel is reserved and the Q.931 SETUP message is built. All digits
must be present before sending the SETUP message. The allocated
B-channel is specified in the channel identifier information element of the
outgoing SETUP message. The SETUP message is sent to the terminating
PRI interface and the B-channel is cut through.
PRI B-channel busy—If all B-channels in the PRI are busy, the call is routed
to the next trunk group in the route list. If no trunk members are available,
route advancement occurs until there are no more choices in the route list.
Then the call is routed to an all circuits busy treatment.
Datafill for B-channel allocation—Datafill in table TRKGRP controls the
allocation of trunk members in either ascending or descending sequential
order. These settings result in one end of the interface selecting trunk
members in ascending sequential order, and the other in descending
sequential order. By datafilling opposite ends of a PRI connection in this
way, glare is minimized. (For more information about glare, see “B-channel
glare” in this chapter.
Non-ISDN originator
If the originator is a non-ISDN trunk, the progress indicator information
element (containing the value “Call is not end-to-end ISDN”) is included in
the outgoing SETUP message.
Terminations and user responses
The following discusses various terminations and user responses.
Terminating to a PRI
When terminating to a PRI, the network may receive a CALL PROC,
ALERT, or CONN message as the first response to an outgoing SETUP
message.
• CALL PROC—When terminating to a PRI, the user receives this
message.
• ALERT—If the network receives this message from the terminating PRI
interface, the network sends an ALERT message over the originating
PRI interface.
• CONN—If the network receives this message from the terminating PRI
interface, the network sends a CONN message to the originating PRI
interface and a CONN ACK to the terminating PRI. The originator may
also respond with CONN ACK. (The user always receives a CONN
ACK in response to a CONN sent to the network.)
Figure 5-5 shows the message sequence between the network and the two
users on a PRI-to-PRI call.