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Paging and Location Update


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Wireless And Mobile Communication

Published in: Mobile
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Paging and Location Update

  1. 1. Paging and Location Update By: Abidullah Zarghoon
  2. 2. Some Terms: • MSC/VLR - Mobile Switching Center / Visitor Location Register • HLR - Home Location Register • PLMN - Public Land Mobile Network • TMSI – Temporary Mobile Subscriber Identity • LA - Location Area • LAI - Location Area Identity • LAC - Location Area Code • LU – Location Update
  3. 3. • MS - The Mobile Station • BSS - The Base Station Subsystem • NSS - The Network Switching Subsystem • OSS - The Operation Support Subsystem
  4. 4. Overview • A GSM or UMTS network, like all cellular networks, is basically a radio network of individual cells, known as base stations. • Each base station covers a small geographical area which is part of a uniquely identified location area.
  5. 5. Location Area • A location area is a set of base stations that are grouped together to optimize signaling • Location Area is a group of cells and the subscriber is paged in this area. • One or more base station controllers are used to serve each Location Area but by a single MSC. • Each Location Area has a unique Location Area Identity number.
  6. 6. Location Area Update • The mobile station also performs location updating, in order to indicate its current location, when it moves to a new Location Area or a different Public Land Mobile Network (PLMN). This location updating message is sent to the new MSC/VLR, which gives the location information to the subscriber's HLR. If the mobile station is authorized in the new MSC/VLR, the subscriber's HLR cancels the registration of the mobile station with the old MSC/VLR.
  7. 7. Location Update Procedure • The location update procedure allows a mobile device to inform the cellular network, whenever it moves from one location area to the next. • Mobiles are responsible for detecting location area codes. • When mobile finds that location area code is different from its last update, it performs another update by sending to the network, a location update request, together with its previous location and TMSI (Temporary Mobile Subscriber Identity)
  8. 8. Periodic Location Update • A location updating is also performed periodically. If after the updating time period, the mobile station has not registered, it is then deregistered. • Each mobile is required to regularly report its location at a set time interval using a periodic location update.
  9. 9. Random Location Update • Whenever a mobile moves from one location area to the next while not on a call, a random location update is required. • This is also required of a stationary mobile that reselects coverage from a cell in a different location area, because of signal fade.
  10. 10. Continued… • When a subscriber is paged in an attempt to deliver a call or SMS and the subscriber does not reply to that page then the subscriber is marked as absent in both the Mobile Switching Center / Visitor Location Register (MSC/VLR) and the Home Location Register (HLR) (Mobile not reachable flag MNRF is set). The next time the mobile performs a location update the HLR is updated and the mobile not reachable flag is cleared.
  11. 11. Paging • Paging is the one-to-one communication between the mobile and the base station • Paging is a procedure the network uses to find out a subscriber’s location before actual call establishment. • Paging is used to alert the mobile station of an incoming call.
  12. 12. • Paging is initiated by the NSS (Network Subsystem) and is based on the Location Registration information the Mobile Subscriber has supplied when performing the Location Update.
  13. 13. Paging Strategies • Location Area Splitting in Paging Areas o Mobile registers only when entering the Location Area; it doesn’t register when moving between Paging Areas of one Location Area. o For an incoming call, paging messages are broadcasted in the Paging Areas according to a sequence determined by different strategies.
  14. 14. Location Area Splitting in Paging Areas
  15. 15. Paging Strategies • Multilayer Location Areas: o Each mobile is assigned to a given group, and each group is assigned one or several layers of Location Areas. o Location Update traffic is distributed over all the cells. o Multilayer Las solves the problem where Location Update traffic is mainly concentrated in the cells of the Location Area border.
  16. 16. Multilayer Location Areas:
  17. 17. Differences between Paging and Location Update • Mobility Management based on pure Paging o If a call arrives, terminal is paged in all cells of the mobile network o Location update is not required o As paging must be executed in all cells of the network for each arriving call/SMS/data- packet • high signaling overhead • high delay in call/SMS/data-packet delivery • Mobility Management based on pure Location Update: o Each time the user crosses cell boundaries a location update is triggered o Paging is not required o As location updates must be initialized whenever crossing cell boundaries • high signaling and database update overhead • high power consumption in the terminals
  18. 18. • Location Update• Paging
  19. 19. Some Definitions • TMSI: o The Temporary Mobile Subscriber Identity (TMSI) is a temporary identification number that is used in the GSM network instead of the IMSI to ensure the privacy of the mobile subscriber • LAI o A Location Area Identity (LAI) is a globally unique number. • LAC o A Location Area Code (LAC) is only unique in a particular network
  20. 20. • Cell: o Cell is the basic service area: one BTS covers one cell. Each cell is given a Cell Global Identity (CGI), a number that uniquely identifies the cell. • MSC/VLR Service Area: o The area covered by one MSC is called the MSC/VLR service area. • PLMN o The area covered by one network operator is called PLMN. A PLMN can contain one or more MSCs. o A network that is established and operated by an administration or by a recognized operating agency (ROA) for the specific purpose of providing land mobile telecommunications services to the public
  21. 21. References: • Advances in Network Management o By Jianguo Ding – 2009