Welltech Dialogic SS7 Protocols ISUP - Manual (Page 13)

Dialogic ® SS7 Protocols ISUP Programmer's Manual Issue 15
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2 General Description
2.1 Module Overview
The ISUP module implements full ISDN User Part functionality. This includes
Call Processing Control (CPC), Circuit Supervision Control (CSC) and
Signalling Procedure Control (SPRC) all of which are fully supported. In
addition, the module implements some Call Control functionality to provide a
clean interface with the user that is defined entirely in terms of ISUP
messages.
Each circuit is identified internally by a Circuit Identifier (cid). Circuit
Identifiers range from zero up to one less than the total number of circuits. A
circuit must be assigned to a circuit group before it can be used.
Circuit groups allow a number of circuits to be configured with common
attributes. They are identified by the group identifier (gid) which ranges from
zero to one less than the total number of circuit groups. Each circuit group
must be assigned an Originating Point Code (OPC) and a Destination Point
Code (DPC), the Circuit Identification Code (CIC) of the first circuit in the
group and the Circuit Identifier (cid) that will be used for this circuit. Further
circuits may be included in the group providing that the CIC of the last circuit
is no more than 31 greater than the first CIC. The circuits do not need to lie
in a contiguous block. The Circuit Identifier cid for each additional circuit will
have the same offset from the first cid as the CIC has from the first CIC.
Each circuit group also has a number of options such as Outgoing/Incoming
Call Priority selection and whether the module is the controlling exchange for
certain timers and features.
All protocol primitives between the application and the ISUP module use a
Call Reference (call_ref) to identify the circuit used for the call. The call
reference is identical to the Circuit Identifier (cid) with the exception that for
messages issued by the ISUP module relating to outgoing calls the most
significant bit of the call_ref is set to one when the ISUP module is configured
for 32768 circuits or less, and the ISPF_16CID flag is set to 0. In all other
cases (more than 32768 circuits configured, or ISPF_16CID flag set to 1), the
cid is identical to the call_reference. The ISUP module now ignores the setting
of the most significant bit of the call_ref and it is recommended that existing
applications which placed significance on this bit be modified to ignore it also.
2.2 Module Configuration
The module is configured for operation by the user in three stages. Initially,
a global configuration message must be sent to the module to configure
environment dependent parameters (in general these parameters will be
fixed for any single application).
Then, an optional message to set the values of protocol timers is issued.
Finally, a configuration message is required for each circuit group before
attempting to originate or accept calls.
The variant of ISUP (e.g. ITU-T, ANSI, national variants or BICC) to be used
for circuits in a group is specified by a configuration parameter in the circuit
group configuration message.