Nortel DMS-250 - Call Establishment at the Originating Exchange; User Call Request

Call control procedures 5-3
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
•
CONN ACK
— User—Sending a CONN ACK message is not mandatory for the user
in response to a CONN.
— Network—CONN ACK is mandatory for the network in response to
a CONN message.
For call control procedures, there are only a few differences between the
network side and the user side. The following information focuses on the
DMS-250 switch as the network; any differences are stated.
If the D-channel data link fails, start timer T309. If the timer expires, clear
the network connection and release the B-channel and call reference.
Call establishment at the originating exchange
Call establishment at the originating exchange means a PRI call comes into
the DMS-250 switch (node 3 in Figure 5-2).
Figure 5-2
Originating exchange
PBX
DMS-250
3
4
IMT
1
25
Basic
PRI
PRI
User Network
UserNetwork
Originating
user user
Terminating
PBX
DMS-250
ISUP
switch
switch
6
(call originates
into switch)
Terminating
exchange
(call terminates
out of switch)
rate
interface
Basic
rate
interface
Originating
exchange
MCI
MCI
Network
User call request
The user requests the call. When a PRI call is received into the switch, it
routes the call based on the call’s SETUP message and the switch datafill.
The SETUP message contains most of the data required to set up the call.
The process of routing requires these main steps:
• analyzing the SETUP message
• determining the call type