,------------------------------------------------------------------------, | Um A | | ,---------, | | ,---------, | | | CM | | CM | | | GSM layer 3 |- - - - -| | | |- - - - -| | | | MM | | MM | | | |- - - - -| | ,-------------------, | |- - - - -| | | | | | | DTAP | | DTAP | | | | RR | | | RR | BSSMAP | | | BSSMAP | | | - - - - - - -|---------| |---------|---------| |---------| | | | | | | | SCCP | | | SCCP | | | GSM layer 2 | LAPDm | | LAPDm |---------| |---------| | | - - - - - - -|---------| | |---------| | | | | | | GSM layer 1 | TDMA | | TDMA | MTP | | MTP | | | `---------' | `-------------------' | `---------' | | BTS BSC | | | | Mobile Station Base Station Subsystem MSC | `------------------------------------------------------------------------'