CSE 535 - PowerPoint PPT Presentation

1 / 19
About This Presentation
Title:

CSE 535

Description:

Cell group organize cells into groups, only update when leaving current group ... There will be always be tradeoffs between cost of search and update operations ... – PowerPoint PPT presentation

Number of Views:51
Avg rating:3.0/5.0
Slides: 20
Provided by: impac1
Category:

less

Transcript and Presenter's Notes

Title: CSE 535


1
CSE 535 Mobile ComputingLecture 7Location
Management
  • Sandeep K. S. Gupta
  • School of Computing and Informatics
  • Arizona State University

2
Location Management
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 cellrequires 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 grouporganize 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 isnt 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 callmobility
    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
Write a Comment
User Comments (0)
About PowerShow.com