Mobile Station at GSM

GSM refers to the cellular handsets as MS.PCMCIA cards are also available for laptop to allow data transfer over GSM network, without the need for a voice-centric handset.
The MS consists of typical equipment that the subscriber uses to access a PLMN and a removable smart card, knows as the SIM to identify the subscriber.

GSM was uniqueto use the SIM card to break the subscriber ID apart from the equipment ID.The SIM card is fully portable between Mobile Equipment (ME) units.This allows many features that we take for granted usch as being able to swap MS simply by swapping our SIM car over.All functionally continues seamless, including billing and the telephone number remains the same

An MS has several associated identities including the International Mobile Equipment Identity (IMEI), the International Mobile Subscriber Identity (IMSI), the Temporary Mobile Subscriber Identity (TMSI) and the Mobile Station ISDN (MSISDN) number


IMEI

Each ME has a unique number known as the IMEI, stored on it permanently.The IMEI is not only a serial number, it is also indicates the manufacturer, the country in which it was produced and the type approval. It is assigned at the factory

The IMEI is used so actions can be taken againts stolen equipment or to reject equipment that it cannot accept for technical and/or safety reason.The IMEI allows tracing and prevention of fraudulent use and in some circumtances,special network handling of specific MS types

Structures of the IMEI:

1.TAC (type approval code)

2.FAC (Final assembly code)

3.SNR (Serial number)


IMSI

Each subscriber is assigned a unique number,which is known as the IMSI.The IMSI is the only absolute identity a subscriber has within GSM and such as it is stored on the SIM.The SIM is a credit size or quarter-credit card size smart card that containts the subscriber's subscription details and grants the subscriber service when placed into a piece of ME.Among other purpose it is used for subscriber billing, identification and authentication when roaming

The structure of IMSI are

1. MCC ( Mobile Country Code)

2.MNC (Mobile Network Code)

3.MSIN (Mobile Station Identification Number)


TMSI

A TMSI is an alias used by the VLR ( and the SGSN in GPRS) enabled networks) to protect subscriber confidentiality.It is temporaily used as a substitute for the IMSI to limit the number of times the IMSI is broadcast over the air interface because intruders could ise the IMSI to identify a GSM subscriber


MSISDN

MSISDN is the number the calling party dial to reach the called party-in other qords it is the mobile usbscriber's directory number.This parameters refer to one of the ISDN number that assigned to a mobile subscriber in accordance with ITU recommandation

The structures of MSISDN are:

1.NDC (National destination code)

2.CC (Country code)

3.SN (Serial number)