2.13.1 Reassembly

Reassembly is process of assembling segments that belongs to same message at destination SCCP. The segments associated to same message are uniquely identified by the reassembly key.

A reassembly key includes the following fields:

• MTP Routing Label (OPC, DPC, SLS)
• Calling Party Address
• Segmentation Local Reference (Unique number generated by originator SCCP and included in Segmentation parameter.

When the first segment of an MSU sequence is received, a reassembly timer TReassembly is started.

The destination SCCP ensures the following:

• The segments are reassembled in correct segmentation order and if out of order segments are received, then reassembly must stop and reassembly error procedure is applied.
• Reassembly process completes in a definite amount of time governed by timer Treassembly. In case of failure in completing within the time, the reassembly stops and reassembly error procedure is applied.