Mobile Station/ Mobile Phone
The mobile station (MS) is not your mobile phone alone; it consists of a mobile phone and your SIM cards. ( SIM= Subscriber Identity Module) . Now in a GSM network, you can switch phones easily by simply inserting your SIM card into another phone. No hassles. That’s because, in a GSM network, your SIM card is attached to the network not your phone.
Now, it isn’t necessary that a SIM card is used for a Mobile phone alone, it can be used for other mobile equipment. I will explain this in my next posts. For now, for the purpose of simplicity, let us consider the Mobile station as a mobile phone+ SIM card.
Every mobile Phone is identified by The IMEI. (International Mobile Equipment Identity). Its like the fingerprint of a phone. You wont find two phones with the same IMEI.
Useful Info: IMEI’s are tracked by the Mobile Operator. It is registered in EIR of your networks MSC.
(EIR= Equipment Identity register)
Just like the IMEI is the fingerprint of the Phone. The IMSI( International Mobile subscriber identity is the fingerprint of the SIM card. The IMSI is used to identify the subscriber to the system, a secret key for authentication, and other information. The IMEI and the IMSI are independent, thereby allowing phones to be interchanged. The SIM card may be protected against unauthorized use by a password or personal identity number( PIN code)