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GSM Mobile Terminated (MT) Call Flow Explained

mobile communication gsm call flow protocol stack mt call

This tutorial section on GSM basics covers the following topics:

Main Page
Frame
Burst types
PHY
GSM stack
Speech processing
ARFCN
Channel types
GSM Security
Network Entry
Mobile basics

Introduction

This article covers the Mobile Originated (MO) and Mobile Terminated (MT) call flow in GSM. This page describes the mobile terminated call flow between the Mobile (UE) and the network.

It covers messages exchanged between Layer 3 entities (RR, MM, CC) on both sides. It includes the 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 has been done between the UE and the Network as described in the GSM tutorial section.

mobile terminated,MT call flow in GSM

As described in the figure, the Paging Channel (PCH) will be sent by the network to alert the mobile with a ring tone if someone dials its number. This is called a mobile terminated call.

After the PCH is received, the mobile will transmit a Random Access Channel (RACH) request and obtain a Standalone Dedicated Control Channel (SDCCH) and other resources for further processing.

As described in the GSM protocol stack, messages flow between both the mobile and the network at various layers (Layer 3, Layer 2, Layer 1 (physical layer)).

The message flow is self-explanatory for establishing the circuit-switched mobile terminated (MT) call in GSM.