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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 1TR6-SI and passed over the 1TR6 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.
3.3.5.
VN2 Route
A VN2 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
requires a DTU-BA which handles its own signalling protocol.
For determining if the related users in both public or private networks are compatible, a
special parameter is transferred over the VN2 link with incoming or outgoing calls. This
parameter is the VN2 Service Indicator (VN2-SI). The VN2-SI is a two byte code which is
derived from the IBSC of the ISPBX internal party. The VN2-SI can be assigned as voice or
data together with some additional values for data such as speed and parity.
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For an incoming call, the VN2-SI 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 VN2-SI and passed over the VN2 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.
3.3.6.
Channel Associated Route
A Channel Associated link is a 2Mbps line, 30B+D (timeslot 16 is used for signalling, timeslot
0 is used for synchronisation). The signalling protocol is handled by the DTU-CA or DTU-PU.
It is used for connection to a public network.
No special parameters are transferred over the CA-link with incoming or outgoing calls to
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