Describe VLR overflow control algorithm for Registration. OR Describe the Registration algorithm of GSM/VLR Write the stepwise procedure of registration in VLR identification algorithm.

Subject: Mobile Computing

Difficulty: Medium

Marks: 4 Marks

1 Answer

When a VLR is full, the incoming mobile users cannot receive cellular services

  • To solve VLR overflow problem, overflow control algorithms O- I, O-II, O-III, and O-IV are presented.

  • An extra flag (1 bit) is required in the HLR records


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Step 1: Registration Request:

Step 1.1 same as step 1 of the normal registration procedure

Step 1.2 V2 is full. V2 follows a replacement policy to select a record to be deleted (u3 in Fig.). The storage for the delete record is used to store u1‟s information. The selected user (i.e., u3) is called overflow user. The replacement policy may be based on various heuristics

Step 1.3 V2 forwards the registration request to the HLR with indication that u3’s record is deleted due to database overflow

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Step 2: Registration Response:

Step 2.1 HLR update the location of u1, and sets the overflow flag in u3’s record

Step 2.2 HLR acknowledges the registration operation and sends u1’s profile to V2.

Step 2.3 V2 sends an acknowledgment to MS

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