MTP functions
MTP level 1 (signalling data link level):
MTP level 2 (signalling link level):
MTP level 3 (signalling network level):
Physical transmission (e.g. 64 kbit/s PCM time slot)
HDLC-type frame-based protocol for flow control, error control (using ARQ), and signalling network supervision and maintenance functions.
Routing in the signalling network (using OPC, DPC) between SPs with level 4 users (see SIO at level 2).