In the field of ISDN customer accesses, various protocols were defined for use in different protocol stacks to suit different needs of a range of services. These different protocol stacks have in common the control-plane, or management-plane if appropriate, and user-plane concept of the ISDN, thus require some coordination between these two planes. This coordination is in particular required, if the OSI Connection-mode Network Service (OSI-CONS) according to Recommendation X.213 [2] is to be provided in an ISDN environment.
For the purpose of coordination of the C-plane, or M-plane if appropriate, with the U-plane, Recommendation I.320 “ISDN Protocol Reference Model (PRM)” [1] defines a function called synchronization and coordination function (SCF) and established an architecture for C- and U-plane coordination.
This Recommendation specifies a state machine which provides synchronization and coordination capabilities based on the handling of network (N-) primitives, rather than processing protocol data units (PDU) used by the layer 3 protocols which form a particular stack. Any C-plane service, or M-plane service if appropriate, and U-plane service whose repertoire of (N-) primitives matches the repertoire of (N-) primitives defined in Recommendation X.213 [2] can be coordinated. In addition, the repertoire of (N-) primitives was enhanced in order to make provision in the coordination process, that a connection is released by means of C-plane call control protocol after completion of the disconnection of the U-plane protocols, avoiding premature interruption of the U-plane information flow. The SCF offers different coordination functionality which can be selected by means of predicates.
This Recommendation does not address the mapping of various cause values in reason parameters contained in primitives and the handling of parameters contained in primitives.
This Recommendation covers Switched Virtual Circuit (SVC) and Permanent Virtual Circuit (PVC) arrangements in the narrow-band and broadband ISDN.
It is expected that there will be a growing demand for such a function since also B-ISDN and TMN may have this coordination problem.