ABSTRACT
Contents 13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390 13.2 General Background Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391 13.3 Location Update Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
13.3.1 Location Update According to Distance . . . . . . . . . . . . . . . . . 393 13.3.2 Location Update According to Movement . . . . . . . . . . . . . . . 393 13.3.3 Location Update According to Time . . . . . . . . . . . . . . . . . . . . . 394 13.3.4 Local Anchoring Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 13.3.5 Reporting Cells Tracking Strategy . . . . . . . . . . . . . . . . . . . . . . . . 395 13.3.6 Alternative Strategy (AS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397 13.3.7 Forwarding Pointer Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397 13.3.8 Eager Caching Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 13.3.9 Hierarchical Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
13.4 Location Management in Third-Generation Wireless Networks (3G UMTS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 13.4.1 Architecture of Intercooperating 2.5G-3G Networks . . . . 399
13.4.1.1 Core Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 13.4.2 3G/UMTS Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 13.4.3 Location Management Strategies . . . . . . . . . . . . . . . . . . . . . . . . . 402
13.5 Location Management Specifications for GSM/UMTS . . . . . . . . . . . . 406 13.5.1 International Mobile Subscriber Identity
(IMSI) Detach/Attach Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 406 13.5.2 General Procedures in the Network Related
to Location Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406 13.5.3 Information Transfer between Visitor and Home
Location Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407 13.5.4 Mobile Subscriber Purging Procedure. . . . . . . . . . . . . . . . . . . . 408
13.6 Location Management Cost Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408 13.6.1 Registration Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 13.6.2 Call Delivery Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410
13.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
13.1 Introduction With the increasing demands for new data services, wireless networks should support calls with different traffic characteristics and different Quality-of-Service (QoS) guarantees. For cellular networks to be able to efficiently cope with mobile user requirements, new mechanisms are needed, mechanisms that will help the network know the location of every mobile user it serves, and thus, properly track the user. Knowing where the user resides, the cellular network will be capable of creating suitable connections (creation of a suitable path) between two users and deliver the call efficiently. Moreover, the cellular network should guarantee low call delivery latency and all time connectivity, especially when a user moves from one cell to another, providing at the same time the appropriate amount of bandwidth and avoiding call termination. The mechanism responsible for carrying out the above procedures is generically called mobility management. This mechanism is divided into the following two procedures: (1) the location management procedure and (2) the handover procedure. The scope of the handover operation is to preserve active users’ connections while they transact from one registration area to another. For that reason, several schemes have been implemented. On the other hand, location management is an operation that frequently informs the network where the users reside. Several strategies have been proposed and implemented for the location management procedure. The main ideas behind these strategies and a detailed analysis of some of them are presented in this chapter. The location management procedure can be further subdivided into the following two categories:
1. Location registration procedure: When a mobile terminal (MT) happens to move, either from one cell to another or from a certain region (RA, registration area) (that contains a certain number of cells)
to another, it sends specific signaling messages to the network to inform it of its current location.
