The entity addressed in the original call set up, which is busy when first called by subscriber A. Similarly, MSC B, VLR B and HLR B are the network elements pertaining to Destination B when Destination B is a GSM mobile.
The queue that manages CCBS requests for a subscriber, when that subscriber is the originator of those CCBS Requests.
Supplementary Service Application Part. SSAP is the protocol used for CCBS procedures on the interface between the originating and destination network. Communication across this interface is performed using SCCP Connectionless Signalling (Refer to ETS 300 358).
The user of MS A, requesting CCBS. Similarly, MSC A, VLR A and HLR A are the network elements pertaining to Subscriber A.
The user of destination B, who may not necessarily subscribe to CCBS.
The user of MS C, who is the forwarded-to-party when call forwarding applies. Similarly, MSC C, VLR C and HLR C are the network elements pertaining to Subscriber C.
The queue that manages CCBS requests for a subscriber, when that subscriber is the target of CCBS Requests.
For each of the service timers, the location, start and stop conditions and action on expiry are given - Refer to clause 5.1
Abbreviations used in this specification are listed in TR 21.905