(i) MSISDN (Mobile Station ISDN number)- A MSISDN uniquely classifies a subscription in the Global System for Mobile Communications (GSM) or Universal Mobile Telecommunications System (UMTS) networks. It is the telephone number of the Subscriber Identity Module (SIM) card displayed on mobile or cellular phones.

(ii) IMSI (International Mobile Subscriber Identity) - Which uniquely identifies the MS. It is used as the key to search any data the databases in VLR, HLR and GSN. An international mobile subscriber identity (IMSI) is a unique number, usually fifteen digits, associated with Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS) network mobile phone users. The IMSI is a unique number identifying a GSM subscriber.

(iii) IMEI (International Mobile Equipment Identity) - IMEI is a 15- or 17-digit code that uniquely identifies mobile phone sets. The IMEI code can enable a GSM (Global System for Mobile communication) or UMTS (Universal Mobile Telecommunications Service) network to prevent a misplaced or stolen phone from initiating calls.

(iv) TMSI (Temporary mobile subscriber identity) - Which is the GPRS equivalent of TMSI in GSM. Temporary Mobile Subscriber Identity for most commonly sent between the mobile and the network.. The TMSI number is local for a specific local area, and need to be updated every time when the mobile moves to a new geographical area. Paging a mobile is the key use of the TMSI.