Scalable Location Management for Large Mobile Ad hoc Networks

Sumesh J. Philip

Contents

Wireless Ad hoc networks Issue of Scalability Geographic Routing

Scalable Location Update based RoutingSLALoM - Scalable Location ManagementGrid Location ServiceHierarchical Grid Location ManagementSimulations and ResultsConclusion

Wireless Ad hoc networks

Infrastructure-less networks that can be easily deployedEach wireless host acts as an independent router for relaying packetsNetwork topology changes frequently and unpredictablyHow to route packets?Quite a lot of protocols proposed in literature (table driven/reactive/hybrid)Dynamic source Routing (DSR) works well for small networks

Issue of Scalability

Increasing density increases average node degree, decreases network diameter Routing cost less Any reasonable scheme might work!

To test scalability, area (playground size) must increase with nodes Average node degree constant Will present a mobility model that

consolidates the above relationship

Traditional Protocols

Table driven incur large overheads due to routing table

maintenance Delayed control as good as no control

On-demand flood the entire network with discovery packets long latency for discovery Path maintenance means additional state

No separation between data and controlUltimately, data suffers!!

Any contenders ?

Not many invariants to play with (IP address, local connectivity)Nodes physically located closer likely to be connected by a small number of radio hopsPossible to obtain node location via a GPS receiverGeographic forwarding Packet header contains the destination’s

location Most forward with fixed radius

Geographic Forwarding

A

B

CD F

C’s radio range

E

G

A addresses a packet to G’s latitude, longitudeC only needs to know its immediate neighbors to forward packets towards G.Geographic forwarding needs location management!

Desirable Properties ofLocation Management

Spread load evenly over all nodesDegrade gracefully as nodes failQueries for nearby nodes stay localPer-node storage and communication costs grow slowly as the network size grows

Scalable Location based Routing Protocol (SLURP)

Hybrid Protocol that has a deterministic manner of discovering the destination

Topography divided into square grids

Each node (ID) selects a home region using f(ID), and periodically registers with the HR

Nodes that wish to communicate with a node query its HR using f--1(ID)

Use geographic forwarding to send data, once location is known (e.g. MFR)

Example

[12]

[10]

- Home region

- Update/Query

- Location Database

- Data

f(ID) - ID Mod(RT)

ID = 22; RT= 12;HR=22%12 = 10;

DST = 22; RT= 12;

HR=22%12 = 10;

Cost of Location Management

Location Registration Periodic Triggered

Location Maintenance Operations for database consistency

Location Discovery Query/response

Data Transfer

Mobility Model

Each node moves independently and randomlyDirection , Velocity [v-c, v+c] at tNew direction and velocity at destinationNode degree =

To keep degree constant, A must grow linearly with N

]20[

NA

rt2

Location update Overhead

region of area

region of side 2

rangeion transmiss

node of velocity

hops ofnumber

costbroadcast

crossingregion of rate

a

R

r

v

u

b

t

R

v

dRCos

v

4

22

21

tr

ab

sec/)( )(cost pdateLocation U ubcu

Location update Overhead

dzzzfz

e

e

zrzf

t

z

r

z

An

tz

)(

1

2)(

0

2

22

regions ofNumber G

region ain nodes Average

region excluded of Area

distance node-intermean

degree node average

progress forwardmost

N

A

n

z

z

)(

)(

)( )(

2

NvO

NRR

R

v

z

dbubc

NRGRd

u

Home Region Maintenance

)( Overhead eMaintenanc

))1(2(4

1 );2(

2

vO

r

a

R

v

bc

t

m

On region crossingInform previous region of departureInform new region of arrivalUpdate from any node in new region

regionper nodes ofnumber Average

nodes ofnumber Total

N

Total Overhead

)(2 2 NOz

ducl

Cost of LocatingSend a Location query to Home region

Total Overhead = Sum of all overheads for all nodes

sec/)(

NvNO

NNNvNNv

cccc lmu

ScaLAble Location Management (SLALoM)

Define a hierarchy of regions : Order(3), Order(2), Order(1)Each Order(2) region consists of K2 Order(1) regionsEach node assigned a HR in an Order(2) regionTo reduce location update overhead, define far and near HRs; near regions updated frequentlyNodes that wish to communicate with another node query its HR in current Order(2) gridQueries from far HRs find way to near ones for exact location of destination

Protocol Operation- Order 3

- Update/Query

- Location Database

- Data

K = 3

- Order 2

- Home region

Control Overhead

)(

))()9((

2

222

1

K

vNvKO

uK

AbubOc fnu

)(

1 );2(1

vO

bcm

Maintenance Overhead Location Update

Cost of Locating

)()(z

KO

z

KOcl

Total Overhead

)(

at minimized );(

3

4

3

1

2

2

vNO

NKK

NvvKNOc

Grid Location Service (GLS)

n

s

ss

s

s

s

s

s s

• s is n’s successor in that square. (Successor is the node with “least ID greater than” n )

sibling level-0squares

sibling level-1squares

sibling level-2squares

... 1

...

...

...

GLS Updates9

23, 2

11, 2

6

9

11

1623

6

17

4

26

21

5

19

25

7

3

292

...

...

...

...

...

...

......

...

1

8

1

location table content

location update

2Invariant (for all levels):For node n in a square, n’s successor in each sibling square “knows” about n.

1

...

...

...

9

23, 2

11, 2

6

9

112

1623

6

17

4

26

21

5

19

25

7

3

292

...

...

...

...

...

...

......

...

1

8

... 1

location table content

query from 23 for 1

GLS Query

HIEARCHICAL GRID LOCATION MGMT

Motivations Current solutions do not scale well or not robust with node

mobility Do not consider localized mobility or local communication needs Although there are grid based solutions, they use a single layer for

location management, and hence can be improvedContributions

Proposed a multi-layer Grid scheme which uses hierarchical location management, suitable for large networks

Analyzed cost for location management overhead Show that the proposed scheme performs better in large, dense

systems

LOCATION REGISTRATION

Nodes in unit grid aware of each other by periodic broadcastNodes located in a region act as location serversHierarchy of a server decided by its position as well as the locale of the regionNodes update servers as they cross grid boundariesNumber of updates, and distance traversed by the updates depends upon boundary hierarchyLocalized movement results in few updates that traverse short distances

Mobile Node

Movement

Update msg

LOCATION MAINTENANCE

On entry into a grid, a node announces its presence

If the unit grid is a server region, a node already present in the region replies with location information that the newly arrived node has to store

Use of timers to avoid a broadcast storm

Mobile Node

Movement

Locationdatabase to store ?

A (A_loc)B (B_loc) …

LOCATION DISCOVERY& DATA TRANSFER

If source, destination located in the same unit grid, they can talk directly

If not, source initiates a query message to discover the location of the destination

Query visits leaders until the approximate location of the destination is known

Data forwarded to the approximate location

Data continues to be forwarded to leaders that have more accurate information of the destination or until it reaches the destination

Response msg

Query msg

Data

PERFORMANCE ANALYSIS: Location Management Overhead

Observations Cost of location management consists of registration, maintenance and

discovery The number of transmissions required per message proportional to distance

traversed by the message An update that resulted from an ith boundary crossing visits at most (i +1)

leader grids for (0 i k ) A query visits at most i leader grids, if source and destination located in the

same ith gridNotations:

progress forward average - z

crossing grid of rate - cost broadcast - b

crossingboundary for )2

log(hierarchy of levels -k

updatefor distance average - d grid nodes/unit average -

gridunit a of side - d Nodes ofNumber - N

2

th

i

iN

LOCATION REGISTRATION COST

Pr[ ith server is updated] =

Average distance traversed by update =

Average number of broadcasts =

Average location update cost =

)1( )12)(21(2

1kiP

iki

i

k

ii DPD

1

kkOk

dk

largefor )()121

)(4

22(2

k

iiiPb

1

kOk

k largefor )1(

122

)( bz

Dcu

c/nodepackets/se )log(

)log(

)())1((

2

2

NvO

NOz

kOO

z

D

LOCATION MAINTENANCE COST

When a node enters a new grid, it broadcasts its presence

A server node will respond with location information to store

In the worst case, all the nodes in the grid will broadcast back the location maintenance message

Pr[node enters a server grid] =

Average location maintenance cost =

4

1

)(1 )1(4

bcm

c/nodepackets/se )(vO

LOCATION DISCOVERY COST

Location query visits at most k leaders

Average distance for query in the kth grid =

Assuming worst case distance in the ith grid,

Average location discovery cost =

k

kk

kk

kddd

2

11

22

1

4

74313224

)4 ...4 (44

3

kd

)2( )4

12(

7

23 kk

kk Od

c/nodepackets/se )(

)2

()(

NvO

zO

z

dc

kk

d

PERFORMANCE ANALYSIS: Simulations (GloMoSim)

Compared against SLURP, a well known protocol in literatureParameter values

Topography size varied from 1000x1000m – 4000x4000m Node density 80 nodes/km2 (unit grid side 250 m) Transmission range 350 m, speed 2Mbps IEEE 802.11 MAC Random Waypoint mobility (Maximum speed 25 m/s, Minimum speed

0 m/s, Pause Time 0s) Random, Constant Bit Rate traffic 1024 bit payload

Performance Metrics Registration overhead, registration delay, data delivery ratio, data delay Results shown for increasing number of nodes

RESULTSRegistration Overhead Registration Delay

Data Delivery Ratio Data Delay

CONCLUSIONS

Cost of location management is important in geographic forwarding based protocols

Designed a multi-level grid ordering scheme for hierarchical location management

Average location registration cost increases only logarithmically in number of nodes for our scheme; hence scales well for large ad hoc networks

Simulations show that our scheme outperforms SLURP

For dense networks, simulations indicate that the protocol is robust with node mobility

For localized movements and local communication needs, hierarchical grid location management should perform even better

References

C. Cheng, S. Philip, H. Lemberg, E. van den Berg, T. Zhang, SLALoM: A Scalable Location Management Scheme for Large Mobile Ad-hoc Networks, to appear in Proceedings of Wireless Communications and Networking Conference, March, 2002 Y. B. Ko, N. H. Vaidya, Location Aided Routing in Ad-Hoc networks, Proceedings of ACM/IEEE Mobicom’98, Dallas, TX, Oct. 1998Josh Broch, David A. Maltz, David B. Johnson, Yih-Chun Hu, and Jorjeta Jetcheva. A Performance comparison of multi-hop wireless Ad-Hoc network routing protocols. In Proceedings ACM/IEEE MobiCom, pages 85-97, October 1998.Jinyang Li, John Janotti, Douglas S. J. De Couto, David R. Karger, and Robert Morris, A Scalable Location Service for Geographic Ad Hoc Routing, The Sixth Annual International Conference on Mobile Computing and Netwroking, pages 120-130, August 2000Seung-Chul M. Woo and Suresh Singh, Scalable Routing in Ad-Hoc Networks, Technical Report, TR00.001, March 2000 Basagni S. and Chlamtac, I. and Syrotiuk, V. R. and Woodward, B. A. A Distance Routing Effect Algorithm for Mobility (DREAM), Proceedings of the Fourth Annual ACM/IEEE International conference on Mobile Computing and Networking, MobiCom'98, pp. 76-84, Dallas, TX, October 25-30, 998K. Fall and K. Varadhan, NS notes and documentation, technical report, UC Berkeley, LBL, USC/ISI and Xerox Parc, 1997. http://www.isi.edu/nsnam/ns