C.1 SCCP segmentation
29.0023GPPMobile Application Part (MAP) specificationRelease 17TS
Instead of one UDT message several XUDT messages are used according to
Signalling Connection Control Part, Signalling System no. 7 ITU-T recommendation (07/96) Q.711 to Q.716 (‘White Book SCCP’).
This mechanism may be used for all MAP messages. If no segmentation mechanism at the TCAP or MAP level is available, this is the only remaining possibility.
This mechanism has no impact on the MAP provider level and above; the MAP provider sees the parameter as being sent in a single segment.
It should be noted that not all SCCP transit nodes (world wide) currently support the transfer of XUDT messages. Therefore XUDT messages may be lost without notice, depending on the route the message takes. The routes which successive messages take between two end points can differ because of load balancing. It is therefore recommended that this mechanism is used only for:
a) messages which do not cross PLMN boundaries (when the PLMN operator ensures that all SCCP transit nodes within his PLMN support White Book SCCP)
b) messages with low priority i.e. loss of the message does not result in serious misoperation.
It should be noted that the decision whether or not a message crosses PLMN boundaries needs to be taken at the MAP application level; it is therefore based on the message’s operation code rather than on the SCCP called party address, i.e. only messages which never cross PLMN boundaries due to the type of message (SendIdentification, SendRoutingInfo without OR, AnyTimeInterrogation, …) can be regarded as not crossing PLMN boundaries.