Call control procedures 5-19
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
If EVS termination is required, the call setup information is sent to the EVS
ARU over the ISDN D-channel in the SETUP message. The SETUP
message contains
• the Generic Address information element, including the dialed number
identification services
• the Generic Digits parameter, including
— the originating trunk group
— the originating switch identifier
• the called party number information element, including:
— the called party number
— the automatic number indicator
The originating switch CLLI, found in table MCLLICDR, is usually located
in the originating trunk group field of the Generic Digits parameter
(provided in the SETUP message). The NCS_SWITCH_ID, found in table
OFCVAR, is usually located in the originating switch identifier field of the
Generic Digits parameter (provided in the SETUP message).
Calls that originate on an EVS switch and are destined for an EVS ARU go
through normal translation procedures to access the network control system
or in-switch routing information through table INWATXLA.
After completing the EVS audio text message sequence, the EVS ARU
instructs the EVS switch to transfer (extend) or to disconnect the call.
Call transfer (extension) on an EVS switch
The ability to transfer (extend) an active call from the EVS ARU to a new
destination is supported for non-VNET calls, but not for VNET calls. The
EVS system can instruct the DMS-250 switch to transfer a call as explained
below:
• A FACILITY message containing the menu digit information collected
by the EVS ARU is sent in addition to the regular sequence of call
transfer messages.
• After the call is transferred, the EVS PRI portion of the call is released
through the ISDN release link trunk messaging sequence.
• Calls that are transferred over ISUP IMT or PRI trunks cannot be
allowed to terminate to an EVS ARU a second time. PTS IMT
interworking is not supported.
When the EVS switch transfers a call from the EVS ARU to a new
destination, the PRI link connecting the EVS ARU to the EVS switch is
released, as shown in Figure 5-11.
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