Routing and Location Managementin Mobile Ad-hoc Networks

By

Sumesh J. Philip(09/20/2001)

Contents

IntroductionRouting Protocols Table Driven (WRP, DSDV) On Demand (DSR, AODV, TORA) Performance Evaluation Geographic (LAR, DREAM)

Location Management for Large Scale Networks (GLS, SLURP, SLALOM)References

Mobile Ad-Hoc Network

Collection of mobile nodes forming a networkNo centralized administration or standard support servicesHighly co-operative, each host is an independent routerHosts use wireless RF transceivers as network interface

Conferences/Meetings

Search and Rescue

Disaster Recovery

Automated Battlefields

MaNet Constraints and Issues

Lack of a centralized entityNetwork topology changes frequently and unpredictablyRouting and Mobility ManagementChannel access/Bandwidth availabilityHidden/Exposed station problemLack of symmetrical linksPower limitation

Conventional Routing Protocols ?

Not designed for highly dynamic, low bandwidth networks“Count-to-infinity” problem and slow convergenceLoop formation during temporary node failures and network partitionsProtocols that use flooding techniques create excessive traffic and control overhead

MaNet Protocols

Proactive Protocols Table driven Continuously evaluate

routes No latency in route

discovery Large capacity to

keep network information current

A lot of routing information may never be used!

Reactive Protocols On Demand Route discovery by

some global search Bottleneck due to

latency of route discovery

May not be appropriate for real-time communication

Wireless Routing Protocol (WRP)

A Path finding algorithm; uses predecessor to destination in the shortest pathEliminates the “Count-to-infinity” problem and converges fasterNeighbor connectivity via periodic “Hello” messagesUpdate messages sent upon detecting a change in neighbor link

Each node i maintains a Distance table (iDjk), Routing table (Destination Identifier, Distance iDj , Predecessor Pj ,the successor Sj), link cost table (Cost, Update Period) Processing Updates and creating Route Table Update from k causes i to re-compute the

distances of all paths with k as the predecessor For a destination j, a neighbor p is selected as

the successor if p->j does not include i, and is the shortest path to j

Operation

J

K

IB

(0, J)

(2, K)

(2, K)

(1, K)

X1110

1

5

10

(, K)

(10, B)

(10, I)

(11, B)

Destination Sequenced Distance Vector (DSDV)

Each Route is tagged with a sequence number originated by destinationHosts perform periodic & triggered updates, issuing a new sequence numberSequence number indicates the “freshness” of a route Routes with more recent sequence numbers

are preferred for packet forwarding If same sequence number, one having

smallest metric used

Topology changes

Broken links assigned a metric of ∞Any route through a hop with a broken link is also assigned a metric of ∞“∞ routes” are assigned new sequence numbers by any host and immediately broadcast via a triggered updateIf a node has an equal/later sequence number with a finite metric for an “∞ route”, a route update is triggered

DSDV Operation

Damping Fluctuations

Routes preferred if later sequence numbers, or smaller metric for same sequence numbersProblem : Table fluctuations if worse metrics are received first, causing a ripple of triggered updatesSolution : Use average settling time as a parameter before advertising routesTantamount to using two tables, one for forwarding packets and another for advertising routes

Dynamic Source Routing (DSR)

Each packet header contains a route, which is represented as a complete sequence of nodes between a source-destination pairProtocol consists of two phases route discovery route maintenance

Optimizations for efficiency Route cache Piggybacking Error handling

DSR Route Discovery

Source broadcasts route request (id, target) Intermediate node action Discard if id is in <initiator, request id> or

node is in route record If node is the target, route record contains the

full route to the target; return a route reply Else append address in route record;

rebroadcast

Use existing routes to source to send route reply; else piggyback

DSR Route Maintenance

Use acknowledgements or a layer-2 scheme to detect broken links; inform sender via route error packetIf no route to the source exists Use piggybacking Send out a route request and buffer route

error

Sender truncates all routes which use nodes mentioned in route errorInitiate route discovery

Optimizations for efficiency

Route Cache Use cached entries

for during route discovery

Promiscuous mode to add more routes

Use hop based delays for local congestion

Must be careful to avoid loop formation

Non propagating RREQs

Optimizations

Piggybacking Data piggybacked on route request Packet Problem : route caching can cause piggybacked

route replies to be discardedImproved Error Handling when network becomes partitioned, buffer

packets and use exponential back-off for route discovery

Listen to route replies promiscuously to remove entries

Use negative information to ignore corrupt replies

Ad-hoc On DemandDistance Vector (AODV)

On demand protocol that uses sequence numbers (DSDV) to build loop free routesKey difference from DSR is that source route is no longer requiredPath discovery Reverse Path setup Forward path setup

Table management and path maintenanceLocal connectivity management

AODV Reverse path setup

Counters : Sequence number, Broadcast idReverse Path Broadcast route request (RREQ) < source_addr,

source_sequence-# , broadcast_id, dest_addr, dest_sequence_#, hop_cnt >

RREQ uniquely identified by <source_addr , broadcast_id>

Route reply (RREP) if neighbor is the target, or knows a higher dest_sequence_#

Otherwise setup a pointer to the neighbor from whom RREQ was received

Maintain reverse path entries based on timeouts

AODV Forward path setup

RREQ arrives at a node that has current route to the destination ( larger/same sequence number) unicast request reply (RREP)<source_addr, dest_addr, dest_sequence_#, hop_cnt,lifetime> to neighborRREP travels back to the source along reverse path each upstream node updates dest_sequence_#, sets up a forward pointer to the neighbor who transmit the RREP

AODV OperationD

S

X

X

Protocol Maintenance

Route Table management Route request expiration timer purges

reverse paths that do not lie on active route Active neighbor relays a packet within

active_route_timeout Route cache timer purges inactive routes New routes preferred if higher destination

sequence number or lower metric

AODV Maintenance

Path maintenance Upon link breakage, affected node

propagates an unsolicited RREP <dest_sequence_#+1, ∞> to all upstream nodes

Source may restart route discovery processLocal connectivity management Broadcasts used to update local

connectivity information Inactive nodes in an active path required to

send “hello” messages

Temporally OrderedRouting Algorithm (TORA)

Link reversal algorithm Destination oriented Directed Acyclic Graph

(DAG) Full/Partial reversal of links

Assigns a reference level (height) to each nodeAdjust reference level to restore routes on link failureMultiple routes to destination; route optimality not importantQuery, Update, Clear packets used for creating, maintaining and erasing routes

Creating Routes

C

A B

E

G (DEST)

FH

D

QRY

QRY

QRY UPD

QRY

QRY

UPD

UPD

UPD

UPD UPD

UPD

Route Maintenance

C

A B

E

G (DEST)

FH

D

UPD

X

UPD

UPD

Erasing Invalid Routes

Performance Analysis

Simulation Environment Network Simulator, 50 nodes in a 1500x300m

rectangular flat grid Random waypoint mobility Constant bit rate traffic

Address resolution : ARP implementation in BSD UnixMedium Access Control : IEEE 802.11 Physical Layer model : combines both free space and two ray ground reflection modelProtocols studied : DSDV(SQ), AODV, DSR, TORA

Performance Analysis

Metrics Packet Delivery Ratio : Ratio of number of

packets generated by CBR sources to that received by CBR sinks at destination

Routing Overhead : number of routing packets sent; each transmission counts as one transmission

Path Optimality : Difference between length of actual path took and the length of the shortest path

Packet Delivery Ratio

95-100% in most cases for DSR, AODVStale route entries in DSDV cause dropsShort lived loops in TORA as part of link reversalAll protocols perform well when there is low node mobility

Routing Overhead (packets)

Route caching and non-propagating RREQs in DSRTORA

Sum of mobility dependant, independent overhead for TORA

Congestive collapse

Nearly constant for DSDV due to periodic updates

Routing Overhead (Bytes)

DSR more expensive than AODV except at high mobilitySmaller packets in AODV, may be more expensive in terms of media access, power and network utilization

Path Optimality

DSDV, DSR use routes close to optimalTORA not designed to find shortest pathTORA, AODV use paths close to optimum when node mobility is low

Geographic Routing

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 systemGeographic forwarding Packet header contains the destination’s

location Most forward with fixed radius

Distance Routing EffectAlgorithm for Mobility (DREAM)

Proactively disseminate location informationDistance Effect :

Closer nodes are updated more frequently “age” field in location update

Mobility Effect : rate of location update controlled by mobility No bandwidth wastage for no movement

Geographic forwarding If no entry for destination in table, flood Otherwise forward data to m neighbors in the

direction of destination

Location Aided Routing (LAR)

On Demand protocol; used restricted flooding for locating destination Flooding is restricted to a “request zone”, defined by an “expected zone”A node forwards a route request only if it belongs to the “request zone”Tradeoff between latency of route determination and message overhead Resorts to flooding when prior information of destination is not available

LAR Scheme 1

Source calculates the “expected zone”, defines a “request zone” in the request packet and initiates route discoveryNode I receiving the route request forwards the request if it falls inside the “request zone”, otherwise discards itWhen destination receives the request, replies with a route reply including current location, time and average speedSize of request zone is large at low and high node speeds

LAR Scheme 2

Source calculates the distance Dists to destination (xd, yd) and initiates route discovery with both parametersNode I calculates it’s distance Disti from (xd, yd) and forwards the request only if Disti<= Dists + δ, otherwise discards the request

Node I replaces Dists with Disti before forwarding the requestNon zero δ increases probability of route discovery

LAR schemes

N

S (xs,ys)

I

J

D(xd,yd)

R = v(t-t0)

N

S (xs,ys)

I

J

Scheme 1 Scheme 2

D(xd,yd)

Issue of Scalability

The number of packets each node has to forward and the amount of state kept at each node grow slowly with the size of the networkMost existing protocols break down for large networksTable driven

incur large overheads due to routing table maintenanceOn-demand

flood the entire network with discovery packets, wastes network resources

long latency for discoveryProtocols which use geographic routing use global flooding to build tables or destination discovery; may not be scalable

Location Management

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 a location service!

Desirable Properties ofLocation service

Spread load evenly over all nodes.Degrade gracefully as nodes fail.Queries for nearby nodes stay local.Per-node storage and communication costs grow slowly as the network size grows

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

Scalable Location based Routing Protocol (SLURP)

Hybrid Protocol that has a deterministic manner of discovering the destinationEach node selects a ‘home region’ using , which maintains the node’s current locationNodes that wish to communicate with a node query its ‘home region’ using Can use most forward with fixed radius without backward progression to send data, once location is known Routing overhead

)(vN 3/2

)(IDf

)(1 IDf

Protocol Operation

[12]

[10]

Scalable Location Management (SLALOM)

Define a hierarchy of grids : Order(3), Order(2), Order(1)Assign a Order(1) ‘home region’ for each node in an Order(2) gridNodes that wish to communicate with another node query its ‘home region’ in their Order(2) gridTo reduce location update overhead, define ‘far’ and ’near’ home regions; ‘near’ regions updated frequentlyRouting overhead )(vN 4/3

Protocol Operation

References

S. Murthy and J.J Garcia Luna Aceves, A Routing Protocol for Packet Radio Networks, Proc. IEEE Mobicom, Nov. 1995Y. B. Ko, N. H. Vaidya, Location Aided Routing in Ad-Hoc networks, Proceedings of ACM/IEEE Mobicom’98, Dallas, TX, Oct. 1998Josch Broch, David B. Johnson, and David A. Maltz. The Dynamic Source Routing protocol for Mobile Ad-Hoc networks, Internet-Draft, draft-ietf-manet-dsr-00.txt, March 1998.Charles Perkins, Ad-Hoc On Demand Distance Vector (AODV) Routing. Internet-Draft, draft-ietf-manet-aodv-00.txt, November 1997.Charles E. Perkins and Pravin Bhagwat, Highly dynamic Destination Sequenced Distance Vector (DSDV) for mobile computers, In Proceedings of the SIGCOMM '94 Conference on Communication Architectures, Protocols and Applications, pages 234-244Josh 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 2000. Seung-Chul M. Woo and Suresh Singh, Scalable Routing in Ad-Hoc Networks, Technical Report, TR00.001, March 2000 V. Park, S. Corson, A Highly Adaptive Distributed Routing Algorithm for Mobile Wireless Networks, IEEE Infocom97 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, 998