Mobile Terminated-MT call flow in GSM
This article covers MO MT call flow in GSM. This page describes mobile terminated call flow between Mobile(UE) and network. It covers messages exchanged between Layer 3 entities(RR,MM,CC) at both side. It include channels(PCH,RACH,AGCH,SDCCH,FACCH,TCH) used at layer 1 to carry these messages over the air. This article assumes that initial frequency and time synchronization is done between UE and Network as described in GSM tutorial in tutorial section.
As described in the figure, PCH will be sent by network to alert mobile with ring tone if someone dials. This is called mobile terminated call. After PCH is received, mobile will transmit RACH and obtain SDCCH and other resources for further process.
As described in GSM protocol stack, messages flow between both mobile and network at various layers(layer 3,layer 2,layer 1(physical layer). The message flow is self explanatory to establish the circuit switched mobile terminated(MT) call in GSM.
Mobile Terminated Call (MT call) Release
The figure above mentions messages exchanged between mobile and network for call release.
MO Call flow in gsm
Refer Mobile Originated Call flow.