Telecom Tutorials by Samir Amberkar

Voice Call continued [Under GSM >> Signaling]

Step 3: TMSI reallocation, Voice Call setup begin, Switching from SDCCH to FACCH of TCH

MS1

BTS1

BSC1

MSC1

VLR1

MAP - Forward New TMSI DTAP (TMSI Reallocation Command) RLM (TMSI Reallocation Command) SDCCH, MM - TMSI Reallocation Command SDCCH, MM - TMSI Reallocation Complete RLM (TMSI Reallocation Complete) DTAP (TMSI Reallocation Complete) MAP - TMSI Ack SDCCH, CC - SETUP RLM (SETUP) DTAP (SETUP) Possible proprietary communication DTAP (Call Proceeding) RLM (Call Proceeding) SDCCH, CC - Call Proceeding BSSMAP - Assignment Request DCM signaling to determine possible channel RLM (Assignment Command)1 SDCCH, RR - Assignment Command FACCH, L2 establish2 FACCH, RR - Assignment Complete RLM (Assignment Complete) BSSMAP - Assignment Complete DCM - release SDCCH

1: This also contain traffic channel related information
2: FACCH is Fast Associated Control CHannel. It is part of TCH (sort of in-band siganling).

We will continue "Voice Call" in next article.

References: GSM Networks book by Heine, GSM book by Mouly and Pautet, Signaling diagrams from 24.007/24.008 (R99).

© Copyright Samir Amberkar 2010

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