GSM Architecture

Network and Cell Information Acquisition
When a mobile station is successful in synchronizations it reads four time-slot long Broadcast Control CHannel (BCCH) for the system information. This channel has a specific time-slot relative to the FCCH/SCH channels. The information in the
BCCH channel includes:
Location Area ID (LAI) o Mobile Country Code (MCC) o Mobile Network Code (MNC) o Location Area Code (LAC)
Cell ID (CID)
BCCH Allocation List (BA list) – a list of neighboring cells’ beacon frequencies
Information about the locations of common control channels (paging, random access and access grant channels)
Frequency hopping Sequence
Maximum mobile station power limit (MSTXPwr)
Base station’s minimum received signal power to access the network (RxLevAM)
Update period (location update)
At this stage an MS is fully furnished with necessary information and synchronization in order to communicate with the network. A mobile station is not yet to be attached to the network. It requires IMSI (International Mobile Subscriber Identity) attach and location update procedure. The IMSI attach procedure lets the network record that the mobile station is powered on and is ready to make or receive calls. The location update procedure lets the network record which location the MS is now anchored. To proceed with those tasks the mobile station must make a service request to the network.

1. MS after dialing a number and press send key uses RACH to ask for a signaling channel.
2. The BSC allocates a signaling channel, using AGCH.
3. The MS sends a call setup request through SDCCH, to the
MSC/VLR. Over SDCCH, all signaling takes place. This includes:
Marking the MS status as active in the VLR (if the MS status is not updated earlier).
The Authentication Procedure
Ciphering
Equipment Identification
Sending the called Subscriber number to the network
Checking if the subscriber has service barring of outgoing calls activated.
4. The