GSM MOBILE STATION (MS)

The Mobile Station consists of two system functional components:

 ·        Mobile Equipment (ME)

 ·        Subscriber Identity Module (SIM) Card

Mobile Equipment (ME) 

The ME is the physical handset that allows the user to access the network. The ME contains the International Mobile Equipment Identity (IMEI), a unique number which is permanently stored and which can identify the hardware within the network.

The capability of the ME depends on the manufactures specification and is identified by the means of a class mark. The class mark is transmitted to the system on the initial message and contains the following information:

Revision Level - identifies the phase of the GSM specifications that the mobile complies with.

RF Power Capability -the maximum power the MS is able to transmit. This information is used to control and prepare the handover sequence.

Ciphering Algorithm -indicates which ciphering algorithm is implemented in the MS. There is one algorithm (A5) in GSM phase 1, but GSM phase 2 specifies different algorithms (A5/O-A5/7).

Frequency Capability - indicates the frequency bands the MS can transmit and receive on.

Short Message Service (SMS) - indicates whether the MS is able to receive SMS. The ability to transmit short messages depends on the manufactures specification.

 

Subscriber Identity Module (SIM) Card

The SIM Card is a “Smart Card” available in two sizes depending on the ME requirement. Both the full size and mini SIM card contain the following information:

IMSI - International Mobile Subscriber Identity - A unique number used to identify the MS subscriber, which is only transmitted during the initial call.

TMSI - Temporary Mobile Subscriber Identity - A Random number changed by the system to protect against “hackers” attempting to interrogate the air interface.

LAI - Location Area Identity - Identifies the location of the MS within the system.

Ki - Subscriber Authentication Key - Used by the system to identify the SN Card.

MSISDN Mobile Station International Services Digital Network - The users mobile phone number comprising of:

 ·          Country Code

·          National Code

·          Subscriber Number

The SIM Card is capable of storing additional information, accessed by the user from the ME, i.e. User created telephone directory. It can also provide a degree of security in the form of a Personnel Identity Number (PIN), which is stored on the card to prevent UN-authorised access.