5-18 Call control procedures
297-2521-106 Standard 23.01 March 2001
Termination capability
EVS termination capabilities are provided for a call if one of the following
occurs:
• an EVS feature code is included in the network control system feature
code parameter (returned to the originating switch in the routing
response message)
• the NARSCALL field of table INWATXLA is set to Y (EVS was
previously called NARS—network audio response system)
If the trunk required for termination is not a dedicated PRI EVS trunk, the
call will be treated as a non-EVS call.
At the EVS switch, calls destined for an EVS ARU are identified by the
TRKGRP field NARSDED in the OPTIONS vector.
The standard Q.931 protocol is used for messaging between the EVS
(terminating) switch and the EVS ARU. Figure 5-10 illustrates a call
origination message sequence provided by this feature.
Figure 5-10
EVS call origination
Originating
switch
EVS switch
EVS
ARU
IAM
SETUP
CALL PROC
ALERT
ACM
CONN
CONN ACK
ANM
Audio text playback
Note: Dashed lines indicate optional messages.
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