January 30, 20071 ECET 581/CPET/ECET 499 Mobile Computing Technologies & Apps Mobility Management 2 of 3 Based on the Text used in the course: Fundamentals

January 30, 2007January 30, 2007 11

ECET 581/CPET/ECET 499ECET 581/CPET/ECET 499 Mobile Computing Technologies & AppsMobile Computing Technologies & Apps

Mobility Management Mobility Management 2 of 32 of 3

Based on the Text used in the course: Fundamentals of Mobile & Based on the Text used in the course: Fundamentals of Mobile & Pervasive Computing, 2005, by Frank Adelstein, et. al, Pervasive Computing, 2005, by Frank Adelstein, et. al,

from McGraw-Hillfrom McGraw-Hill

Lecture 5Lecture 5

Paul I-Hai Lin, Professor Paul I-Hai Lin, Professor Electrical and Computer Engineering TechnologyElectrical and Computer Engineering Technology

Indiana University-Purdue University Fort WayneIndiana University-Purdue University Fort Wayne


Mobility Management Mobility Management (cont.)(cont.)

Mobile Location CodeMobile Location Code• Mobile Country CodeMobile Country Code• Mobile Network CodeMobile Network Code• Local Area CodeLocal Area Code• Routing Area CodeRouting Area Code• Cell IdentifyCell Identify

Location Update ProcedureLocation Update Procedure• A mobile device inform a cellular network A mobile device inform a cellular network

whenever it moves from one location area to whenever it moves from one location area to anotheranother

• Mobiles are responsible for detecting location Mobiles are responsible for detecting location area codearea code



Periodic Location UpdatePeriodic Location Update• Each mobile is require to regularly report Each mobile is require to regularly report

its location at a set time intervalits location at a set time interval Radom Location UpdateRadom Location Update

• When a mobile moves from one location area When a mobile moves from one location area to the next while not on a callto the next while not on a call

• A stationary mobile that selects coverage from A stationary mobile that selects coverage from a cell in a different location area because of a cell in a different location area because of signal fadingsignal fading

RoamingRoaming• A Mobility management procedure of all cellular A Mobility management procedure of all cellular

networksnetworks



TMSITMSI (Temporary Mobile Subscriber Identity) (Temporary Mobile Subscriber Identity)

• Given to the mobile, the moment it is switched Given to the mobile, the moment it is switched onon

• Local to location areaLocal to location area• Has to be updated, each time the mobile moves Has to be updated, each time the mobile moves

to a new geographical areato a new geographical area IMSI (International Mobile Subscriber Identify)IMSI (International Mobile Subscriber Identify)

• A unique number associated with GSM and A unique number associated with GSM and UMTS network mobile phone usersUMTS network mobile phone users

• The number is stored in SIM (Subscriber The number is stored in SIM (Subscriber Identity Module) cardIdentity Module) card



Location Management Principles Location Management Principles & techniques& techniques• Location Registrars (databases)Location Registrars (databases)• Location AreaLocation Area

A set of base stations (10s or A set of base stations (10s or even 100s)even 100s)

Grouped for optimized signalingGrouped for optimized signaling• Search OperationSearch Operation• Update operationUpdate operation

Static Update SchemesStatic Update Schemes Dynamic Update SchemesDynamic Update Schemes


Simple Location Management Scheme Simple Location Management Scheme (cont.)(cont.) Search and Update Operations (mobile node m Search and Update Operations (mobile node m

is switched on) – Static Updateis switched on) – Static Update

Home Location Registrar

(a) Registration upon mobile switching on

Base-station(cell d)Base-station

(cell c)

Mobile m is in cell cI a

m in

yo

ur c

ell

m is switched on Mobile m’s trajectory


Simple Location Management Scheme Simple Location Management Scheme (cont.)(cont.)

Search and Update Operations (mobile node Search and Update Operations (mobile node moves from cell c to cell d)moves from cell c to cell d)


(b) Registration upon cell handoff

Mobile m’s trajectory


(cell c)

I wan

t to

be in

you

r cel

l

Mobile m is in cell d

Found m!


Simple Location Management Scheme Simple Location Management Scheme (cont.)(cont.)

Search and Update Operations (m in cell c & ON)Search and Update Operations (m in cell c & ON)


(c) Another mobile wants to find m – success case



(cell c)

2

1 Where is mobile m?

Is mobile m in your cell?

Pag

e m

34

Find m 5

I am

her

e

6


Simple Location Management Scheme Simple Location Management Scheme (cont.)(cont.) Search and Update Operations (find m location; m is Search and Update Operations (find m location; m is

OFF)OFF)


(d) Another mobile wants to find m – a failure case

M is switched-offMobile m’s trajectory


(cell c)

2

1 Where is mobile

m?


Pag

e m

3

4 Did not find m

5 Failure to find m

January 30, 2007January 30, 2007 1010

Mobility Binding of a Mobile NodeMobility Binding of a Mobile Node How to reduce the probability of failure How to reduce the probability of failure

(1 – max, 0 – min)?(1 – max, 0 – min)? Enhancement 1 – reduce search cost Enhancement 1 – reduce search cost

through the # of updates performed at through the # of updates performed at HLR per mobile nodeHLR per mobile node• tU – the time when the binding was last tU – the time when the binding was last

updatedupdated• ttL – the time to live (how long the binding is ttL – the time to live (how long the binding is

valid)valid)• tP – periodically update time < ttLtP – periodically update time < ttL

January 30, 2007January 30, 2007 1111

Mobility Binding of a Mobile Node Mobility Binding of a Mobile Node (cont.)(cont.)

How to reduce the probability of failure (1 How to reduce the probability of failure (1 – max, 0 – min)?– max, 0 – min)?

Enhancement 2 – page neighbor cellsEnhancement 2 – page neighbor cells• Increasing areas/cells for a maximum of k Increasing areas/cells for a maximum of k

ringsrings• If the speed of mobile node m is a maximum If the speed of mobile node m is a maximum

of vm cells per second, then k can be set toof vm cells per second, then k can be set to

k = vm x tpk = vm x tp

January 30, 2007January 30, 2007 1212

Registration Area-based Location Registration Area-based Location ManagementManagement

Used by Personal Communication Service Used by Personal Communication Service - GSM- GSM

Service areas of PCs – the set of all cells Service areas of PCs – the set of all cells (the union of coverage area of all the cells)(the union of coverage area of all the cells)• Partitioned into several Registration Areas Partitioned into several Registration Areas

(RAs) or Location Areas(RAs) or Location Areas• Each RA consists of several contiguous Each RA consists of several contiguous

communication cellscommunication cells

January 30, 2007January 30, 2007 1313

Registration Area-based Location Registration Area-based Location Management Management (cont.)(cont.)

Base-station(cell c)


(1) Registration upon mobile switching on

Mobile m


21

Where is mobile m?


Mobile m is in RA1

Mobile m is in RA2

Base-station(cell e)

Base-station(cell d)

3 4

(2) Mobile is being located (3) Cell handoff but no registration with HLR(4) Registration upon crossing RA boundary

Reg

iste

r me

in y

our

cell

I am

her

e

Reg

iste

r me

in y

our c

ell

Pag

e fo

r m

Pag

e fo

r m

Pag

e m

e fo

r m

m is

in c

ell c

Mobile m is in RA1

Registration Area 1 (RA1) Registration Area 2 (RA2)

January 30, 2007January 30, 2007 1414


Cell c & d – in RA1Cell c & d – in RA1 Cell e – in RA2Cell e – in RA2 Node m moves from cell c to dNode m moves from cell c to d

• Average update cost is reduced, because the Average update cost is reduced, because the HLR is not informed when handoff involves HLR is not informed when handoff involves cells belonging to same RAscells belonging to same RAs

• Search cost is increased, because all the cells Search cost is increased, because all the cells in the RA have to be contacted for the exact in the RA have to be contacted for the exact location of the mobile nodelocation of the mobile node

January 30, 2007January 30, 2007 1515


2-Level Hierarchy of Location Registrars2-Level Hierarchy of Location Registrars• Local Location RegistrarsLocal Location Registrars• Remote Location RegistrarsRemote Location Registrars

Used in GSM to avoid contacting all the cells in Used in GSM to avoid contacting all the cells in the RA to locate a mobile nodethe RA to locate a mobile node• One Location Registrar One Location Registrar ↔ 1 RA↔ 1 RA• One Location Registrar One Location Registrar ↔ several RAs (in practice) ↔ several RAs (in practice) • N Registration Areas (RA1, RA2, …, RAn)N Registration Areas (RA1, RA2, …, RAn)• N Local Location Registrars (LR1, LR2, …, LRn) N Local Location Registrars (LR1, LR2, …, LRn) • LRi is the Local Location Registrars of RAiLRi is the Local Location Registrars of RAi• All others location registrars as Remote Location All others location registrars as Remote Location

Registrars Registrars

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Location ManagementLocation Management

Home Location RegistrarsHome Location Registrars Visitor Location RegistersVisitor Location Registers Forwarding PointersForwarding Pointers Per-user CachingPer-user Caching

January 30, 2007January 30, 2007 1717

Actual Address vs. Forwarding PointerActual Address vs. Forwarding Pointer Alice in & moves quite often (every week) – Alice in & moves quite often (every week) –

Texas: Dallas Texas: Dallas → → El Paso El Paso → → Austin Austin → → HoustonHouston• Maintaining a forwarding location pointer: reduce the Maintaining a forwarding location pointer: reduce the

burden of Local Updating cost for Aliceburden of Local Updating cost for Alice BobBob

• Increasing the Remote Search CostIncreasing the Remote Search Cost• Contact NY Registrar first, then contact Texas Contact NY Registrar first, then contact Texas

RegistrarRegistrar Which Method is better?Which Method is better?

• Actual Address at Home Location RegistrarActual Address at Home Location Registrar• Forwarding Pointer (Location pointer)Forwarding Pointer (Location pointer)

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Actual Address vs. Forwarding Pointer Actual Address vs. Forwarding Pointer (cont.)(cont.)

Figure 2.3 (1) Maintaining actual address at HLR (courtesy: http://www.infoplease.com/atlas/

unitedstates.html)

El pasoHouston

Austin

Dallas

NY-LR

Tx-LR

Alice: If Never Changeaddress in TX *Maintain the Actual addr atHome LR: NY Is better!

Bob:

→ NY LR

January 30, 2007January 30, 2007 1919

Actual Address vs. Forwarding Pointer Actual Address vs. Forwarding Pointer (cont.)(cont.)

Figure 2.3 (2) Maintaining forwarding pointer at Home Location Registrar (HLR)

(courtesy: http://www.infoplease.com/atlas/unitedstates.html)

El pasoHouston

Austin

Dallas

NY-LR

Tx-LR

1

2

Alice moves often: Dallas, El Paso, Austin, Houston

* Maintain a location pointer at NY

Bob: contact

Tx-LR for subsequent loc. info

January 30, 2007January 30, 2007 2020

A Chain of Forwarding PointersA Chain of Forwarding Pointers AliceAlice

• Maintaining Forwarding Pointers of length 3Maintaining Forwarding Pointers of length 3• New York New York → Texas → Alaska → Alabama→ Texas → Alaska → Alabama

BobBob• Trying to locate AliceTrying to locate Alice• Start with New York registrar then follow the Start with New York registrar then follow the

forwarding pointers forwarding pointers • For 4 location registrars New York → Texas For 4 location registrars New York → Texas

→ Alaska → Alabama → Alaska → Alabama

January 30, 2007January 30, 2007 2121

A Chain of Forwarding Pointers A Chain of Forwarding Pointers (cont.)(cont.)

Figure 2.4 Location management using a chain of forwarding pointer(courtesy: http://www.infoplease.com/atlas/unitedstates.html)

1

2

3

4

January 30, 2007January 30, 2007 2222

Static vs Dynamic Update SchemesStatic vs Dynamic Update Schemes Static Update SchemeStatic Update Scheme

• RA-based Location UpdateRA-based Location Update• Ignore dynamic behavior of mobile nodesIgnore dynamic behavior of mobile nodes• Boundaries of RAs are predetermined (static)Boundaries of RAs are predetermined (static)• Cost: a lot of location update due to mobile Cost: a lot of location update due to mobile

nodes moving between two adjacent RAs in nodes moving between two adjacent RAs in quick successionquick succession

Dynamic Update SchemesDynamic Update Schemes• Time-based (periodic) UpdatesTime-based (periodic) Updates• Movement-based UpdatesMovement-based Updates• Distance-based UpdatesDistance-based Updates

January 30, 2007January 30, 2007 2323

Dynamic Update SchemesDynamic Update Schemes Time-based (periodic) UpdatesTime-based (periodic) Updates

• Update Control TimerUpdate Control Timer• The simplest method to implementThe simplest method to implement

January 30, 2007January 30, 2007 2424

Dynamic Update SchemesDynamic Update Schemes Movement-based UpdatesMovement-based Updates

• A mobile node update A mobile node update its locationits location

• When? When? It crosses a certain It crosses a certain

number of cell number of cell boundaries M since boundaries M since it last registeredit last registered

• MechanismMechanism Counting the number Counting the number

of Handoffs since the of Handoffs since the last updatelast update

• Suitable for stationary Suitable for stationary usersusers

1

2

3

4

1

2

3

4

1

2

3

4Boundary 1

Boundary 2

Boundary 4

Boundary 3

M

January 30, 2007January 30, 2007 2525

Dynamic Update SchemesDynamic Update Schemes Distance-based UpdatesDistance-based Updates

• A mobile node updates its A mobile node updates its locationlocation

• When?When? It moves a certain number of It moves a certain number of

cells D away from the last cells D away from the last cell at which it last updated cell at which it last updated its locationits location

• Need to know the topology Need to know the topology of cellular networkof cellular network

• Difficult to implementDifficult to implement• Suitable for mobile user Suitable for mobile user

who moves within a who moves within a localitylocality

6

7

5

1

2

3

4

6

7

5

1

2

3

4

6

7

5

1

2

3

4

* Last update at Cell 1

* Update at Cell 4 after moved D cells away

D

January 30, 2007January 30, 2007 2626

Dynamic Update Schemes Dynamic Update Schemes (cont.)(cont.)

Per-User Location Caching (on the mobile)Per-User Location Caching (on the mobile)• Used to avoid accessing a roaming mobile’s Used to avoid accessing a roaming mobile’s

location frequentlylocation frequently• CMR (Call-to-Mobility Ratio) = CMR (Call-to-Mobility Ratio) =

(Avg rate at which a user received calls) over (Avg (Avg rate at which a user received calls) over (Avg rate at which the user moves)rate at which the user moves)

• LCMR (Local CMR) = LCMR (Local CMR) = (Avg rate at which a user receives calls from a (Avg rate at which a user receives calls from a

given Registration Area) over (Avg rate at which given Registration Area) over (Avg rate at which the user moves)the user moves)

• RCMR (Regional CMR) = RCMR (Regional CMR) = Same definition as that of the LCMRSame definition as that of the LCMR

January 30, 2007January 30, 2007 2727

Replicating Location Information Replicating Location Information (cont.)(cont.)

Location info stored at one of the n Location Location info stored at one of the n Location RegistrarsRegistrars

Load balancing of RegistrarsLoad balancing of Registrars Replicating info & methodsReplicating info & methods

• Redundancy – failed registrars (for example, hit by Redundancy – failed registrars (for example, hit by the storm)the storm)

• How many replicas?How many replicas? Full replication – increase the cost of updatesFull replication – increase the cost of updates Partial replication – preferablePartial replication – preferable

• Methods of replication Methods of replication Flat OrganizationFlat Organization Hierarchical OrganizationHierarchical Organization

January 30, 2007January 30, 2007 2828


Flat OrganizationFlat Organization• Given n Location RegistrarsGiven n Location Registrars• If a mobile node info can be stored any LR, If a mobile node info can be stored any LR,

without any penalty in terms of access costwithout any penalty in terms of access cost• An Example: An Example:

n = 16 LRsn = 16 LRs k Replication Factor = 4 (k k Replication Factor = 4 (k ≤ n)≤ n) Update starts at the randomly selected LR6 → Update starts at the randomly selected LR6 →

LR10 → LR14 → LR2LR10 → LR14 → LR2 Search for the same mobile node starts at Search for the same mobile node starts at

randomly selected location registrar, sequentially, randomly selected location registrar, sequentially, LR12 → LR13 →LR14 (found it)LR12 → LR13 →LR14 (found it)

January 30, 2007January 30, 2007 2929


Flat OrganizationFlat Organization

LR0

Figure 2.6 Search and update in a location management system with flat organization.

First LR to store mobiles location info (randomly selected)

LR1LR2

LR3 LR4 LR5

LR6

LR7

LR15LR14

LR13 LR12 LR11 LR10LR9

LR8

(k-1) remaining LRs updated at the stide of n/k

First LR to search is randomly selected

Following at most n/k-1 LRS searched in sequential

January 30, 2007January 30, 2007 3030


Hierarchical OrganizationHierarchical Organization• Multi-level (tree) of LRsMulti-level (tree) of LRs• Leaf LR: has info on all the mobile nodes in Leaf LR: has info on all the mobile nodes in

the RA(s) associated with itthe RA(s) associated with it• Root LR: stores info on all the mobile nodes in Root LR: stores info on all the mobile nodes in

the systemthe system An ExampleAn Example

• 15 LRs: LR0 … LR15 formed a balanced tree15 LRs: LR0 … LR15 formed a balanced tree• 8 RAs (RA0, RA1, …, RA7)8 RAs (RA0, RA1, …, RA7)• Caller – LR4Caller – LR4• Callee – LR1 (before move), LR2 (after move)Callee – LR1 (before move), LR2 (after move)• Location Info maintained at LR1, LR6, LR12, Location Info maintained at LR1, LR6, LR12,

and LR14and LR14

January 30, 2007January 30, 2007 3131


Hierarchical OrganizationHierarchical Organization

LR0

Figure 2.7 Update and search in a hierarchical (Tree) location management system.

Update starts at the root LR and proceeds till new LR of the mobile.

LR1 LR2 LR3 LR4 LR5 LR6 LR7

LR14

LR13LR12

LR11LR10LR9LR8

Caller search ends at LCA of caller’s and callee’s LR

Caller’s location registrar

Callee’s location registrar before

move

Callee’s location registrar after

move

January 30, 2007January 30, 2007 3232


The The Search Scenario (in Fig. 2.7)Search Scenario (in Fig. 2.7)• Caller – LR4 in RA4Caller – LR4 in RA4• Callee mobile node – in Ra1Callee mobile node – in Ra1• Search operationSearch operation

In the order: LR4, LR10, LR13, and LR14 In the order: LR4, LR10, LR13, and LR14 (root)(root)

Callee moves from RA1 to RA2Callee moves from RA1 to RA2 The Location info needs to be updated in: The Location info needs to be updated in:

LR14, LR12; LR14, LR12; Added to LR7 and LR2Added to LR7 and LR2 Deleted from LR6 and LR1Deleted from LR6 and LR1

Documents

January 30, 20071 ECET 581/CPET/ECET 499 Mobile Computing Technologies & Apps Mobility Management 2 of 3 Based on the Text used in the course: Fundamentals