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Termination to a PBX
When calls terminate to the PBX, it is sometimes necessary to identify
information that is uniquely related to the call type so the call can satisfy
translations requirements unique to the PBX.
VNET service identifier
VNET calls must be identified with additional information so that the call
can be controlled correctly by the PBX.
The specific information required by the PBX is provided by the integrated
services access (ISA) route selector. ISA route selector is datafilled in the
appropriate routing tables (HNPACONT, RTEREF or OFRT). The ISA route
selector specifies (on a call-by-call basis) information related to the call type
and to information associated with the particular type of call. For VNET,
800, 900, and TIE (trunk connection between two PBXs) calls, the extra
information required is the service identifier. The service identifier is
datafilled in a subfield of the ISA route selector. This subfield is the
FACNUM field and must be datafilled to match the service route of the
SL-1. (Refer to the PBX coordinator to determine the service route
appropriate for VNET calls.)
The following example shows the use of the ISA route selector to provide
the service identifier for VNET calls. The service identifier of 5 is used to
send to the SL-1 PBX. There can be only one SID per call type.
TABLE OFRT
20 ISA
N
Termination to a non-ISDN trunk
When a call terminates from a PRI to non-ISDN trunk, the following
conditions apply to the messages listed.
PROG message—This message is sent after the CALL PROC message is
sent to the originating PRI. PROG contains a progress indicator
information element with the value "Call is not end-to-end ISDN" (as
shown in Figure 5-6).
If the DMS-250 switch is forced to reselect another non-ISDN trunk
after terminating to a non-ISDN trunk, a second progress message is
sent. If the call reselects a PRI trunk group, the call remains "not
end-to-end ISDN" and no additional messages are sent.
ALERT message—This message is not sent. This is because there is no
way of knowing whether alerting is actually taking place on the called
station when calling out over a per trunk signaling trunk.
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
N
N
VNET
5
D2SPRI
Call control procedures 5-13
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