Nortel DMS-250 - Page 281

NCAUUI 14-7
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
Figure 14-4
NCAUUI Invocation Rejection from Network
Originating PBX
DMS-250
SETUP (NCAUUI Request)
RELease COMPlete w/value cause of 42
“switching equipment congestion”
Originating PBX
DMS-250
SETUP (NCAUUI Request)
RELease COMPlete w/value cause of 21
“call rejected”
RELease COMPlete
NOT ISDN PRI AGENCY
Originating PBX
DMS-250
SETUP (NCAUUI Request)
RELease COMPlete w/value cause of 50
“requested facility not subscribed”
TSC RESOURCES ARE ALL BUSY
Originating
user not
subscribed
NCAUUI Congestion and Flow Controls
NCAUUI supports two types of congestion control: user congestion and
network congestion flow control. The PRI user that receives a Q.931
Congestion Control message cannot distinguish whether the originator of the
message is the far-end user or the DMS-250 switch.
When necessary, the DMS-250 switch or the end user controls the transfer of
User Information messages by means of a Congestion Control message. The
Q.931 Congestion Control message contains a Congestion Level IE that can
be set to “Receiver Not Ready” indicating congestion or “Receiver Ready”
indicating congestion clearing. The Q.931 Congestion Control message also
contains an optional Cause IE.