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Describe the mobility databases HLR and VLR. OR Describe mobility database of GSM in detail.

Subject: Mobile Computing

Difficulty: Medium

Marks: 4 Marks


1 Answer
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The home location register (HLR) is database used for mobile user information management. All the permanent subscriber data are stored in this database other than a secret key. An HLR record consists of three types of information.

1. Mobile station information: It stores IMSI (International Mobile Subscriber Identity) used by mobile station to access the network and the MSISDN (Mobile Station - ISDN) which is ISDN number - the "phone number" of cm MS.

2. Location information: It stores the ISDN number (address) of the VLR where the MS resides and the ISDN number of the MSC where the MS resides.

3.Service Information: It stores the information such as service subscription, service restriction and supplementary services. The visitor location register (VLR) is a database which consists of information about service area visited by the MS. The VLR contains all the data which is needed by the MS for call handling and other purposes. Similar to HLR, the VLR information also consists three types of information.

  1. Mobile station information: It stores information such as IMSI, MSISDN and TMSI (temporary mobile subscriber identity) as defined in GSM.

  2. Location information: It stores information such as MSC number and the location area Id (LAI).

  3. Service information: Service information which is a subset of service information stored in the HLR. In the MS related fields, TMSI, structure can be determined by each operator, but the length is eight digits. LAI consists of 3 digit mobile country code (MCC), two or three digit mobile network code, and location access code of 16 digits.

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