1 / 19

CSE 598/494 – Mobile Computing Systems and Applications Class 13 : Location Management

CSE 598/494 – Mobile Computing Systems and Applications Class 13 : Location Management. Sandeep K. S. Gupta School of Computing and Informatics Arizona State University. Agenda. Location management Managing the mobile phone connectivity to the cell tower during user mobility.

chance
Télécharger la présentation

CSE 598/494 – Mobile Computing Systems and Applications Class 13 : Location Management

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CSE 598/494 – Mobile Computing Systems and ApplicationsClass 13:Location Management Sandeep K. S. Gupta School of Computing and Informatics Arizona State University

  2. Agenda • Location management • Managing the mobile phone connectivity to the cell tower during user mobility

  3. Location Management (Ch2) • Fundamental ideas: • Mobile hosts (MH) are served by base stations (BS) (also called access points (AP) • Mobile hosts can roam about the network • Mobile hosts (or other parties) must locate mobile hosts to communicate with them • Involves finding the base station currently serving the mobile host • Search operation • When a mobile host moves, must let the system know where it is • Update operation (also called registration) • Must allow mobile hosts to switch between base stations to support roaming • Handoff operation

  4. Location Information • MH will be served by one BS at a time • BS coverage is one cell • Location information can be maintained at various granularities • One cell—requires MH to update location every time it moves from one cell to another • Tradeoff: more accurate location info vs. a large number of updates, which may overwhelm the system • Cell group—organize cells into groups, only update when leaving current group • Tradeoff: less accurate location info, which will require paging every BS in the group, fewer updates, so less load on the system

  5. Tradeoffs • There will be always be tradeoffs between cost of search and update operations • More updates == more accurate location info == less cost for search • Fewer updates == less accurate location info == more cost for search

  6. Handoff • Handoffs between BSs are required to support roaming • There isn’t necessarily a one-to-one correspondence between handoffs and updates • Issues: • When to handoff? • Selecting a new BS • Allocation of resources such as channels • Informing old BS so that packets destined for MH can be forwarded

  7. Handoff (2) • Mobile controlled handoff vs. • Network controlled handoff • Handoff may be necessary because: • Mobile host is moving • Current BS is overloaded • Quality of communication with current BS is poor

  8. Handoff (3) • Choosing a new BS: • Based on signal strength • Base on predicted movement of MH • Based on resources available at BS

  9. Location Registrars • Location Registrars (LR) are databases containing location information for MHs • Can be one or many • To get the idea, consider a system with only one LR, a Home Location Registrar • Location is maintained at single-cell granularity

  10. Single LR Scheme: Switching ON

  11. Single LR Scheme: Handoff

  12. Single LR Scheme: Search

  13. Single LR Scheme: Search Failure

  14. Enhancements to Single LR Scheme • Can add a timestamp and time-to-live to registration information • TTL (not same as residence time of node in cell) • Helps in constraining the search cost • Search diameters = max speed x ttl • Related to concept of soft-state • Hard-state – explicit revocation of “state” • Soft-state – implicit revocation of “state” • Makes the system more fault-tolerant – adaptive to changes in system • If time-to-live expires, then location for mobile host is assumed out of date • Can expand the search to neighboring cells when attempting to locate a MH

  15. Registration Area-Based Location Management Registration area == a group of cells; update only when crossing a registration area boundary

  16. Properties of RA based approach • Advantages • Reduces update cost • Bounds the search cost (number of cells queried) • Search is restricted to an RA • Makes LM more scalable • By reducing nos of regs to be processed by the HLr • Makes LM more manageable (as compared to per-user LM schemes) • Issues: • Granularity of RA (how to configure system into multiple RAs) • Same size (homogeneous) or different size (in terms cells)? • Optimization problem: how to partition the cells into RAs taking into account call+mobility pattern so as to optimize “LM cost”.

  17. Other Optimizations • Movement-based update (non-RA based) • Update location when MH crosses a specified number of cell boundaries • Distance-based update (non-RA based) • Update location when MH moves a specified distance away from the last point of update • Time/Movement/Distance-based schemes are per-mobile user based schemes. In contrast to these, RA based scheme looks at aggregate mobility and call patterns. • Forwarding pointers • When maintaining multiple location registrars, use a chain of forward pointers to track the MH • Replication of location registrars • Flat • Hierarchical

  18. Flat Replication

  19. Hierarchical Replication Non-leaf nodes cache all info in attached subtrees

More Related