Introduction To Ad Hoc Networks and

Routing Protocols

Presented By :Karthik Samudram Jayaraman

Introduction• What is Ad Hoc Network?

• In Latin, ad hoc means "for this," further meaning "for this purpose only.”

• All nodes are mobile and can be connected dynamically in an arbitrary manner.

• No default router available.• Potentially every node becomes a router: must be able to forward traffic on behalf of others.

Two types of wireless networks • Infrastructured network:

A network with fixed and wired gateways. When a mobile unit goes out of range of one base station, it connects with new base station.

• Infrastructureless (ad hoc) networks:All nodes of these networks behave as routers and take part in discovery and maintenance of routes to other nodes.

Why is Ad Hoc hard?

• Because of a constantly changing set of nodes – Routing is a major issue!

• Security new vulnerabilities, nasty neighbors.• Power running with batteries, little computing

power.

The Desired Properties of Protocols (For Routing)

1. A routing protocol should be distributed.2. Assume routes as unidirectional links.3. Power efficient.4. Consider its security.5. Hybrid protocols can be preferred.

Two Main categories of Protocols

1. Table Driven Routing ProtocolsPro-active, learn the network’s topology before a forwarding request comes in

2. On-Demand Routing ProtocolsRe-active, become active only when needed

Destination Sequenced Distance Vector Algorithm (DSDV)

1. Based on Bellman-Ford Next Hop Routing.

2. Each Node Maintains Tables for :A. Next Hop on PathB. Distance (in hops) to destination.C. Sequence Number ( keep current route)

DSDV contd…

3. Nodes Exchange Updates With Neighbours

• Full Routing Updates• Incremental Updates

ClusterHead Gateway Switch Routing

• Adds hierarchical structure having DSDV as underlying routing algorithm.• Routing is performed over clusterheads and not individual nodes.• Requires Table to maintain cluster Membership, in addition to other routing tables.• Cluster heads are selected by a Least Cluster Change Algorithm to minimize routing changes

Wireless Routing Protocol

• Each node maintains a distance table, a routing table, a link-cost table and a message retransmission list.

• Distance table of node i: (matrix)For each destination j and each neighbor of i(k)• Distance to j

Wireless Routing Protocol

• Routing table of node i is a vector:• The destination’s identifier• The distance to the destination• The predecessor and successor of the chosen

shortest path

Wireless Routing Protocol

• Link-cost Table:• The cost of relaying information through each

neighbor • Message retransmission list:

• One or more retransmission entries

Wireless Routing Protocol

• Information Exchanged among nodes:(routing table update messages )

• Identifier of the sending node• A sequence number assigned by the sending

node• An update list of updates or ACKs to update

message • A response list of nodes that should send an

ACK to the update message

Wireless Routing Protocol

• Each node will communicate with its neighbors reporting any changes in the system

• Each node will keep track of which node should send an acknowledgement

• Nodes will keep track of the changes in the system by periodic transmission of ‘hello’ messages

• This protocol will force nodes to do consistent check of their predecessor hence avoiding count-to-infinity problem.

DSDV

DSDV is based on idea of classical Bellman-Ford Routing Algorithm

Each node maintains a routing table listing all available destinations. The attributes of each destination are the next hop, the number of hops to reach to the destination, and a sequence number, which is originated by the destination node.

Both periodic and triggered routing updates to maintain table

Problems of Distance Vector

Pro-active routing based on Distance Vector

• Topology changes are slowly propagated• Count-to-infinity problem

• Moving nodes create confusion:• they carry connectivity data which are wrong at new

place

• Table exchange eats bandwidth

DSDV

How DSDV addresses the problems?• Tagging of distance information:

• The destination issues increasing sequence number• Other nodes can discard old/duplicate updates

• Changes are not immediately propagated• Wait some setting time

• Incremental updates instead of full table exchange

What is “on-demand”

• The routes are created when required• The source has to discover a route to the

destination.• The source and intermediate nodes have to

maintain a route as long as it is used.• Routes have to be repaired in case of

topology changes.

On-Demand Routing Protocols

1. Ad hoc On-demand Distance Vector Routing

2. Dynamic Source Routing Protocol 3. Temporally Ordered Routing Algorithm 4. Associativity Based Routing 5. Signal Stability Routing

Ad Hoc On-demand Distance Vector Routing

• AODV includes route discovery and route maintenance.

• AODV minimizes the number of broadcasts by creating routes on-demand

• AODV uses only symmetric links because the route reply packet follows the reverse path of route request packet.

• AODV uses hello messages to know its neighbors and to ensure symmetic links.

The node discards the packets having been seen

source

destination

The source broadcasts a route packetThe neighbors in turn broadcast the packet till it reaches the destination

Reply packet follows the reverse path of route request packet recorded in broadcast packet

RREQ

RREP

Route Maintenance

• If the source node moves, it reinitiates the route discovery.

• If intermediate node moves, its upstream node sends a RREP to the source. The source restarts the route discovery.

Dynamic Source Routing Protocol

• A node maintains route caches containing the routes it knows.

• Include route discovery and route maintenance.

Route discovery• The source sends a broadcast packet which contains source address, destination address, request id and path. • If a host saw the packet before, discards it.• Otherwise, the route looks up its route caches to look for a route to destination, If not find, appends its address into the packet, rebroadcast,• If finds a route in its route cache, sends a route reply packet, which is sent to the source by route cache or the route discovery.

destination

source1

65

4

3

2

8

7

(1,4)

(1,2)

(1,3)

(1,3,5,6)(1,3,5)

(1,4,7)

source broadcasts a packet containing address of source and destination

The route looks up its route caches to look for a route to destinationIf not find, appends its address into the packet

The destination sends a reply packet to source.

The node discards the packets having been seen

How to send a reply packet

• If the destination has a route to the source in its route cache, use it

• Else if symmetric links are supported, use the reverse of route record

• Else if symmetric links are not supported, the destination initiates route discovery to source

Route maintenance

• Whenever a node transmits a data packet, a route reply, or a route error, it must verify that the next hop correctly receives the packet.

• If not, the node must send a route error to the node responsible for generating this route header

• The source restart the route discovery

Add entries into route cache

• The Source and destination in route discovery

• Intermediate hosts in route discovery• The hosts receiving any broadcast

Temporally Order Routing Algorithm

• Creating Routes: query/reply• QRY packet is flooded through network• UPD packet propagates back if route exist

• Maintaining Routes: link-reversal• UPD packets re-orient the route structure

• Erasing Routes• CLR packet is floodthrough network to erase

invalid routes

a

fe

d

c

b

h

g

(-,-,-,-,d)

(-,-,-,-,b)

(-,-,-,-,c)

(-,-,-,-,f)(-,,-,-,-e)

Only the non-NULL node (destination) responds with a UPD packet.

(0,0,0,0,h)

(-,-,-,-,a)

The source broadcasts a QRY packet with height(D)=0, all others NULL

(0,0,0,4,b)

(0,0,0,4,c)

(0,0,0,3,e) (0,0,0,2,f)

(0,0,0,2,d)(0,0,0,3,a)

source

Dest.

A node receiving a UPD sets its height to one more than UPDSource receives a UPD with less height

UPD

QRY

QRYQRY

(-,-,-,-,g)(0,0,0,1,g)

TORA: Height metric

• Each node contains a quintuple• Logical time of a link failure• Unique ID of the node that defined the new

reference level• Reflection indicator bit• A propagation ordering parameter, height• Unique ID of the node

Route Maintenance and Erasing• No reaction necessary if all nodes still have downstream

links.

• A new reference level is defined if a node loses its last downstream link.

• Synchronized clock is important, accomplished via GPS or algorithm such as Network Time Protocol.

• CLR packet to be flooded to clear the invalid packet.

a

fe

d

c

b

h

g

(0,0,0,0,h)

(0,0,0,4,b)

(0,0,0,4,c)

(0,0,0,3,e)(0,0,0,2,f)

(0,0,0,2,d)(0,0,0,3,a)

Dest.

(0,0,0,1,g)

Link failure with no reaction

fe

d

c

b

h

g

(0,0,0,0,h)

(0,0,0,4,b)

(0,0,0,4,c)

(0,0,0,3,e)(0,0,0,2,f)

(0,0,0,2,d)(0,0,0,4,s)

Dest.

(0,0,0,1,g)

Re-establishing route after link failure

(1,d,0,0,d)A new reference level is defined

UDPas

UDP

(0,0,0,3,a)(1,d,0,-1,a)(1,d,0,-2,s)

Associativity Based Routing

• Each route keeps a associativity table• A high value of associativity tick indicates a

low state of node mobility• A route is selected based on associativity

states of nodes, finds the high value of associativity tick (low mobility routes)

Associativity table

• All nodes generate periodic beacons• When a neighbor node receives a beacon, it

increases its associativity tick with respect to the sending node in associativity table

• Associativity ticks are reset when the neighbors of a node or the node itself move out of proximity

Route Discovery

• The source broadcast a QRY message• Each intermediate node appends its address

and associativity ticks to QRY,• The destination can examine the

associativity ticks to select route. If the multiple paths have the same overall degree of stability, select the minimum number of hops

Route Erasing

• If the the route is no longer desired, the source may not be aware of any route node changes because partial reconstruction.

• The source node initiates a route delete (RD) broadcast to erase the invalid route.

Conclusion

• DSR has lower routing load than AODVBecause AODV has to depend on route discovery more often, DSR limits the overhead by using route cache

• TORA is higher because its overhead is the sum of neighbor discovery plus routing creating and maintenance

• DSR and AODV perform well than TORA, delivering over 95% packet regardless of mobility rate.

• TORA is lower because the link-reversal process fails in the routing maintenance.

• TORA has a better performance in the less sources.

• The overhead of TORA is worst. It has a better delivery ratio in less sources.

• DSR is good at all mobility rate and movement speed. Its performance is poor in a higher load.

• AODV performs almost as well as DST at all mobility rates and movement. It depends more on route discovery which may increase overhead in

• network

Advantage and Disadvantage

On-Demand AODV DSR TORA ABR SSR Overall complexity

Medium Medium High High High

Overhead Low Medium Medium High High Loop-free Yes Yes Yes Yes Yes Beaconing requirements

No No No Yes Yes

Multiple route support

No Yes Yes No No

Routes maintained in

Route table Route cache Route table Route table Route table

Route reconfiguration methodology

Erase route; notify source

Erase route; notify source

Link reversal; route repair

Localized broadcast query

Erase route; notify source

Routing metric

Freshest and shortest path

Shortest path Shortest path Associativity and shortest path and others

Associativity and stability

Overview

Reference1. Routing Protocols for Ad Hoc Mobile Wireless Networt by Padmini Misra,

ftp://ftp.netlab.ohio-state.edu/pub/jain/courses/cis788-99/adhoc_routing/index.html#CBRP2. A Comparison of On-Demand and Table Driven Routing for Ad-Hoc Wireless

Networks, by Jyoti Raju  and J.J. Garcia-Luna-Aceves, http://www.soe.ucsc.edu/~jyoti/paper2/

3. A New Routing Protocol for the Reconfigurable Wireless Networks, Zygmunt J Hass4. Caching strategies in on-demand routing protocols for wireless ad hoc networks, by

Yih-chun hu and Divid B. Johnson, http://monarch.cs.cmu.edu5. Highly Dynamic Destination-Sequenced Distance-Vector Routing for Mobile

Computers, Pravin Bhagwat, Charles E. Perkins6. Dynamic source routing in ad hoc wireless networks, by David B. Johnson and David

A. Maltz, http://www1.ics.uci.edu/~atm/adhoc/paper-collection/johnson-dsr.pdf7. A Performace Comparison of Multi-Hop Wireless Ad Hoc Network Routing

Protocols, Josh Broch etc8. An Efficient Routing Protocol for Wireless Netwrok, Shree Murthy etc9. Temporally-Ordered Routing Algorithm (TORA) Version 1 Funtional

Specification,  by V. Park, S. Corson, http://www1.ics.uci.edu/~atm/adhoc/paper-collection/corson-draft-ietf-manet-tora-spec-00.txt

10. Ad Hoc On Demand Distance Vector (AODV) Routing, by Charles Perkins, http://www1.ics.uci.edu/~atm/adhoc/paper-collection/perkins-draft-ietf-manet-aodv-00.txt

Reference (cont.)7. An Introduction to Mobile Ad Hoc Network, by Ming Yu Jiang,

http://kiki.ee.ntu.edu.tw/mmnet1/adhoc/8. Scalable Routing Strategies for Ad hoc Wireless Network, by Atsushi Iwata , Ching-

Chuan Chiang etc.9. A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing

Protocols, by Josh Broch, David A. Maltz, David B. Johnson, Yih-Chun Hu, Jorjeta Jetcheva, http://www1.ics.uci.edu/~atm/adhoc/paper-collection/johnson-performance-comparison-mobicom98.pdf

10. Fisheye State Routing: A Routing Schema for Ad Hoc Wireless Networks, by guangyu Pei, Mario Gerla, Tsi-Wei Chen

11. A review of current Routing protocols for ad-hoc Mobile Wireless Networks, by Elizabeth M. Royer and C-K Toh http://www.cs.ucsb.edu/~vigna/courses/CS595_Fall01/royer99review.pdf

12. CEDAR: a Core-Extraction distributed Ad Hoc Routing Algorithm, Prasun Sinha, Vaduvur Nharghavan, etc

13. Mobile computing today & in the future, by M.J. Fahham and M.K. Hauge. http://www.doc.ic.ac.uk/~nd/surprise_95/journal/vol4/mjf/report.html

14. Performance Comparison of On-demand Routing Protocols in Ad Hoc Network by Sohela Kaniz http://fiddle.visc.vt.edu/courses/ecpe6504-wireless/projects_spring2000/pres_kaniz.pdf