Telecommunication has a broad field and it contain different areas like Optical fiber network, mobile and wireless network and satellite network etc. We have considered wireless network specially for GSM network, GSM or global system for mobile communication is a 2G network but when it provides GPRS (data) service it can call 2.5G network.
The 1G network or AMPS has so many vulnerabilities like eavesdropping and handset cloning because it was work on analog domain while the 2G network works on digital environment and uses different sort of encryption algorithm to protect the data.
It is good practice to first describe the initial architecture of GSM network so that you can easily understand the security holes. Now consider the basic diagram.
SIM Subscriber Identity Module HLR Home Location Register MS Mobile Station VLR Vistor Location Register BTS Base Transceiver Station EIR Equipment Identity Register BSC Base Station Controller AC Authentication Center MSC Mobile services Switching Center PSTN Public Switched Telecomm Network VLR Visitor Location Register ISDN Integrated Services Digital Network
Just like a computer network, GSM network also use some authentication process to allow SIM (user) to enter into the network, just assume there are 4 operator that provides GSM services and you have purchased a connection from 1 service provider, now it does not mean that your mobile phone cannot detect the signal of other three network, your cell phone can get the signal of 4 operators but it only can connect to the network of that appropriate SIM because the network identify its user by SIM.
- Mobile Country Code (MCC)
- Mobile Network Code(MNC)
- Mobile Subscriber Identity (MSIN)