A interface
Signalling in GSM core
network
MAP
TCAP
MM /
CM
RR
BSSMAP
/ DTAP
MAP
ISUP
BSSAP
TCAP
BSSAP
SCCP
MTP
SCCP
MTP
BSC
MSC / VLR
to GMSC
HLR
SCCP
SCCP
MTP
ISUP for signalling between exchanges (MSC, GMSC)
MAP for signalling
to/from databases (VLR, HLR, AuC, EIR)