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Components of GSM/CDMA:

Mobile Station:

     This is your mobile or tablet or modem connected to GSM/CDMA Network.

 

Base Station Subsystem (BSS):

      It consists of Base Transceiver Station and Base Station Controller

 

Base Transceiver Station:

     This is the network to which mobile is connected to.

This is the Base Station which receives the signal from Mobile Station and forwards to BSC. It performs as Router while you are connected to internet.This is the Base Station which receives the signal from Mobile Station and forwards to BSC. It performs as Router while you are connected to internet.

     It has antennas in 3 sectors Alpha,ß and Gamma. Antennas are placed in 0,120 and 180 degrees or (60,120,180) degrees based on the users in the area. If there are many users, there may be four sectors. Airtel has four sectors in Mumbai as default due to demand.

    BTS uses either Microwave antenna or optic fiber to connect to other tower.

    For example, if you are in last desk and want to pass the book to first desk, you will pass to anyone in the desk before you, he will pass to a person in the desk before him, it goes on till it reaches the person on the first desk.

    The same thing happens on the mobile. Your mobile will be connected to the sector which is facing you, then your Base Transceiver will send it to next BTS, next BTS will receiver will receive the information and send it to next BTS, it will happen until it reaches Base Station Controller.

   0.6 Meter Microwave dish used for connecting to another tower or Base Station Controller which is nearer to it. 0.6 Meter Microwave dish used for connecting to another tower or Base Station Controller which is nearer to it.

 

 1.2 Meter dish is used for connecting to another BTS/BSC which is far in distance1.2 Meter dish is used for connecting to another BTS/BSC which is far in distance

 

Base Station Controller:

       Each district has one Base Station Controller. In metros like Chennai, there may be two BSC. It allocates frequency to each BTS.

BSC which connects BTS and MSC. BSC which connects BTS and MSC.

 

Mobile Station Subsystem:

       It is the Core Network. It consists of

        1.Mobile Switching Center:

             Each operator has one or two Mobile Switching Centers in each state. Whenever you make a call, it has to go to Mobile Switching Center, even when you are making calls to the person near you. Whereas in BSNL Landline, it gets switched in local switch if you make a call to a local number, trunk switch is used for making STD calls.

        2. HLR:

             It stores your details like your address, balance, current cellular number you are connected to, Call charges, booster in use,  whether you have incoming and outgoing facility, Eligibility for making ISD calls etc.,

        3.VLR:

             It is the replica of HLR. For eg: If you are moving from Tamil Nadu to Andhra, the details stored about you in Tamil Nadu HLR will move to Andhra's VLR

        3. Equipment Identity Register:

                If someone loses his/her mobile, a police complaint is filed, then the complaint is moved to Cyber crime department. They forward the IMEI of lost mobile to all operator's EIR. When the person who stole the mobile tries to connect to network, it scans IMEI and finds that it was the lost mobile, hence it creates an alert.

        4. AuC:

                It is used to verify the SIM card. Each SIM card has A3 and A5 code stored, the same will be stored in HLR which will be used for authentication. Verification will happen once you switch ON the phone and every time you make a call.

                Each operator uses either A3 or A5 algorithm.

                These keys are used for encryption.

                AuC
Ref: SlideshareAuC Ref: Slideshare

 

GMSK:

    If a call is made from one operator to other, then these calls are routed through a G-MSC. Kindly note that calls between same operator (eg: Reliance mobile to Reliance mobile), it will not go through G-MSC.

    If you make calls from mobile to landline, then it will go through G-MSC (even if you make calls from Bsnl mobile to bsnl landline and vice versa).

 

Components of 3G network:

       In 3G, BTS is called as Node-B, BSC as Remote Network Controller, remaining will be similar to 2G network.

        In 3G, each Node-B and RNC will be assigned an IP-address.