Call control procedures 5-25
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
Figure 5-14
PRI-to-PRI disconnect, user initiates normal call clearing
Network User
REL COM
REL
DISC
Billing is now completed.
Cancel T308 and lockout timers and
release B-channel call reference.
Network frees the NETWORK
connection. The trunk member is
idled; the B-channel is
disconnected; and the T308 and
lockout timers are started.
The lockout timer (trunk guard timer) is datafilled in the table TRKSGRP as
TRKGRDTM. (The value is typically less than 2.5 seconds.) For
information about what occurs when the lockout timer expires, see
“B-channel lockout” in this chapter.
When the network receives a REL COM message from the user, the
B-channel and call reference are deallocated; both are free to be allocated for
other calls.
Network-initiated normal call clearing
When the network initiates call clearing, the following occurs:
• A DISC message is sent to the user.
• The network
— disconnects the B-channel
— deallocates the trunk member
— starts timer T305 and the lockout timer; the B-channel is not
available for other calls
After receiving a REL message from the user, the network cancels T305 and
releases the B-channel and call reference. The B-channel is now available
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