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CPET 565 Mobile Computing SystemsCPET 565 Mobile Computing Systems
Mobility Management (2)Mobility Management (2)
Lecture 5Lecture 5
Hongli Luo Hongli Luo Indiana University-Purdue University Fort WayneIndiana University-Purdue University Fort Wayne
Mobility Management Mobility Management (cont.)(cont.)
Location AreaLocation Area• A set of base stations (10s or even 100s)A set of base stations (10s or even 100s)• Grouped for optimized signalingGrouped for optimized signaling• A unique Location Area Code is assignedA unique Location Area Code is assigned• Also called registration areaAlso called registration area
Location Update ProcedureLocation Update Procedure• A mobile device is switched onA mobile device is switched on• A mobile device inform a cellular network whenever it A mobile device inform a cellular network whenever it
moves from one location area to another moves from one location area to another • Mobiles are responsible for detecting location area codeMobiles are responsible for detecting location area code
RoamingRoaming• A Mobility management procedure of all cellular networksA Mobility management procedure of all cellular networks
Mobility Management Mobility Management (cont.)(cont.)
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
Mobility Management Mobility Management (cont.)(cont.)
Location Management Principles Location Management Principles & techniques& techniques• Location Registrars (databases)Location Registrars (databases)• Location AreaLocation Area• 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 OperationsSearch and Update Operations• Uses a single-location registrar to maintain the Uses a single-location registrar to maintain the
location information of all the mobile nodes.location information of all the mobile nodes.• home location registrar (HLR)home location registrar (HLR)• The location of a mobile node is maintained at the The location of a mobile node is maintained at the
granularity of a cellgranularity of a cell• Mobility (m,c)Mobility (m,c)
C – latest cell of mobile node m known to the C – latest cell of mobile node m known to the HLRHLR
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)
Home Location Registrar
(b) Registration upon cell handoff
Mobile m’s trajectory
Base-station(cell d)Base-station
(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)
Home Location Registrar
(c) Another mobile wants to find m – success case
Mobile m’s trajectory
Base-station(cell d)Base-station
(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)
Home Location Registrar
(d) Another mobile wants to find m – a failure case
M is switched-offMobile m’s trajectory
Base-station(cell d)Base-station
(cell c)
2
1 Where is mobile
m?
Is mobile m in your cell?
Pag
e m
3
4 Did not find m
5 Failure to find m
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
binding(m,c, tu, ttl)binding(m,c, tu, ttl)• 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
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
Registration Area-based Location Registration Area-based Location ManagementManagement
Used by Personal Communication Service Used by Personal Communication Service (PCS) - GSM(PCS) - 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
Registration Area-based Location Registration Area-based Location Management Management (cont.)(cont.)
Base-station(cell c)
Home Location Registrar
(1) Registration upon mobile switching on
Mobile m
Mobile m’s trajectory
21
Where is mobile m?
Is mobile m in your cell?
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)
Registration Area-based Location Registration Area-based Location Management Management (cont.)(cont.)
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
Registration Area-based Location Registration Area-based Location Management Management (cont.)(cont.)
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 the RA Used in GSM to avoid contacting all the cells in the RA to locate a mobile nodeto 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 Registrars All others location registrars as Remote Location Registrars
Accessing a local location registrar is less expensive Accessing a local location registrar is less expensive than accessing a remote location registrarthan accessing a remote location registrar
Location ManagementLocation Management
Home Location RegistrarsHome Location Registrars Visitor Location RegistersVisitor Location Registers Forwarding PointersForwarding Pointers Per-user CachingPer-user Caching
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)• Depends on whether Alice moves more often than Depends on whether Alice moves more often than
she is being contacted by some other person.she is being contacted by some other person.
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
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
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
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
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
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• Not suitable for stationary usersNot suitable for stationary users
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
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
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
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
Replicating Location Information Replicating Location Information (cont.)(cont.)
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)
Replicating Location Information Replicating Location Information (cont.)(cont.)
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
Replicating Location Information Replicating Location Information (cont.)(cont.)
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, LR8, LR12, Location Info maintained at LR1, LR8, LR12,
and LR14and LR14
Replicating Location Information Replicating Location Information (cont.)(cont.)
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
Replicating Location Information Replicating Location Information (cont.)(cont.)
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 LR9 and LR2Added to LR9 and LR2 Deleted from LR8 and LR1Deleted from LR8 and LR1