Mumbai University > Computer Engineering > Sem 6 > Mobile Communication & Computing

Marks: 4 Marks

Year: Dec 2016

Call Setup in a GSM Network:

Brief introduction of various elements included in this process.

1. BTS-BTS stands for Base Transceiver Station.It is nothing but your Tower which radiates the signal to your mobile.It is the first player in this operation which always have a touch with the mobile.

2. BSC-BSC stands for Base Station Controller.It is a large unit which controls all the BTS(Towers).We can say that a number of BTS are controlled by a single BSC.There are so many BSCs present in an area depending on the number of users and all are inter connected.

3. MSC-MSC stands for Mobile Switching Center.It is responsible for switching the call to the called subscriber.A number of BSCs are connected to the MSC and it controls the BSC.

4. HLR-HLR stands for Home Location Register.It is the server which stores the details of the all the subscribers permanently.

5. VLR-VLR stands for Visitor Location Register.It is the server which stores the details of the all the visiting subscribers temporarly.

All the above said units are interconnected and plays a vital role in call connection.

Call Setup:

1. When a subscriber initiates a call by dialling a number in his mobile it directly send a request to the BTS which he comes under.

2. BTS there by sends the request to the BSC to which it is connected.

3. From the BSC the request is made to the MSC to which it is connected.

4. Then MSC sends a request to the HLR to check the information about the caller like account balance(if pre paid),live user,area of the caller etc.

5. After checking all the details the HLR sends a acknowlegement message to the MSC that the caller is O.K. to make a call or not.

6. If that message is O.K. the operation continues or else the MSC sends a NOT O.K. message to the BSC which has made the request and BSC to the BTS and BTS to the Mobile.At the next instance the call get disconnected.

7. If the message recieved by the MSC is O.K. then it again sends a request to the HLR to find the called party(the subscriber to whom call is made).

8. The called party and the caller may comes under the same MSC or different MSC.If both comes under the same MSC then the HLR finds the subsciber easily and informs the MSC that to which area the called party belongs.The MSC therefore establishes a air link between the both parties.Thus the call gets connected.

9. If both parties comes under different MSC then the HLR again search for the MSC to which the called party belongs and inform the same to the MSC of the caller.Thus the MSC of the caller establishes a air link between the both parties.Thus the call gets connected.

10. After the call gets disconnected the Billing is made the Billing Server which is present in the HLR.