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comprises an Internal Service Identification Code (ISIC) and an Internal Basic Service
Category (IBSC). The ISIC is passed through to the destination port. The IBSC is used for
compatibility determination.
-
For an outgoing call, the calling port supplies an ISIC, which together with the ports IBSC
form an ISI. The ISI is translated into a SIC and passed over the DASS 2 link.
The translation tables used are given in appendix A.
For more information on the routing aspects and on the Service Indicator Code: see Facility
Implementation Manual; Networks and Routing.
3.3.2.
ISDN Route
An ISDN link is used for connection to a private or a public network. The link can be either:
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A 2Mbps line, 30B+D (timeslot 16 is used for signalling, timeslot 0 is used for
synchronisation). This requires a DTU-PH which handles its own signalling protocol.
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A 192kbps line, 2B+D (16kbps D channel used for signalling, 48kbps overhead). This uses
a DTU-BA or DTX-I. The signalling protocol handled is by the DTU-PH or DTX-I.
For determining if the related users in both networks are compatible, a special parameter is
transferred over the ISDN link with incoming or outgoing calls. This parameter is the External
Service Indicator (ESI). The ESI is a two byte code which is derived from the IBSC of the ISPBX
internal party. The ESI can be assigned as voice or data together with some additional values
for data such as speed and parity.
-
For an incoming call, the ESI is translated into an Internal Service Identifier (ISI). The ISI
comprises an Internal Service Identification Code (ISIC) and an Internal Basic Service
Category (IBSC). The ISIC is passed through to the destination port. The IBSC is used for
compatibility determination.
-
For an outgoing call, the calling port supplies an ISIC, which together with the ports IBSC
form an ISI. The ISI is translated into a ESI and passed over the ISDN link.
The translation tables used are given in appendix A.
For more information on the routing aspects and on the Service Indicator Code: see Facility
Implementation Manual; Networks and Routing.
3.3.3.
DPNSS No.1 Route
A Digital Private Network Signalling System No.1 (DPNSS No.1) link is a 2Mbps line, 30B+D
(timeslot 16 is used for signalling, timeslot 0 is used for synchronisation). It is used for
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