ad-hoc on-demand distance vector

8/12/2019 Ad-hoc on-Demand Distance Vector

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Ad-hoc On-demand Distance Vector

Ad-hoc On-demand Distance Vector(AODV) routing is a routing protocol for Mobile

Ad-hoc Networks(MANETs) and other wireless ad-hoc networks. It is jointl de!eloped

in Nokia "esearch #enter of $ni!ersit of #alifornia% &anta 'arbaraand $ni!ersit of

#incinnatib #. erkins and &. as *+,. A is capable of both unicast and /ulticast

routing. It is a reacti!e routing protocol% /eaning that it establishes a route to a

destination onl on de/and. In contrast% the /ost co//on routing protocols of the

Internet are proacti!e% /eaning the find routing paths independentl of the usage of the

paths. A is% as the na/e indicates% a distance-!ector routing protocol. A a!oids

the counting-to-infinity proble/ of other distance-!ector protocols b using se0uencenu/bers on route updates% a techni0ue pioneered b &.

In A% the network is silent until a connection is needed. At that point the network

node that needs a connection broadcasts a re0uest for connection. ther A nodes

forward this /essage% and record the node that the heard it fro/% creating an e1plosion

of te/porar routes back to the need node. 2hen a node recei!es such a /essage and

alread has a route to the desired node% it sends a /essage backwards through a

te/porar route to the re0uesting node. The need node then begins using the route that

has the least nu/ber of hops through other nodes. $nused entries in the routing tables are

reccled after a ti/e.

2hen a linkfails% a routing error is passed back to a trans/itting node% and the process

repeats.

Much of the co/ple1it of theprotocolis to lower the nu/ber of /essages to conser!e

the capacit of the network. 3or e1a/ple% each re0uest for a route has a se0uence

nu/ber. Nodes use this se0uence nu/ber so that the do not repeat route re0uests that

the ha!e alread passed on. Another such feature is that the route re0uests ha!e a 4ti/e

to li!e4 nu/ber that li/its how /an ti/es the can be retrans/itted. Another such
http://en.wikipedia.org/wiki/Mobile_ad_hoc_networkhttp://en.wikipedia.org/wiki/Mobile_ad_hoc_networkhttp://en.wikipedia.org/wiki/Wireless_ad-hoc_networkhttp://en.wikipedia.org/wiki/University_of_California%2C_Santa_Barbarahttp://en.wikipedia.org/wiki/University_of_Cincinnatihttp://en.wikipedia.org/wiki/University_of_Cincinnatihttp://en.wikipedia.org/wiki/AODV#_note-0%23_note-0http://en.wikipedia.org/wiki/Unicasthttp://en.wikipedia.org/wiki/Multicasthttp://en.wikipedia.org/wiki/Distance-vector_routing_protocolhttp://en.wikipedia.org/wiki/DSDVhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Broadcasting_(computing)http://en.wikipedia.org/wiki/Broadcasting_(computing)http://en.wikipedia.org/wiki/Broadcasting_(computing)http://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Communications_protocolhttp://en.wikipedia.org/wiki/Communications_protocolhttp://en.wikipedia.org/wiki/Mobile_ad_hoc_networkhttp://en.wikipedia.org/wiki/Mobile_ad_hoc_networkhttp://en.wikipedia.org/wiki/Wireless_ad-hoc_networkhttp://en.wikipedia.org/wiki/University_of_California%2C_Santa_Barbarahttp://en.wikipedia.org/wiki/University_of_Cincinnatihttp://en.wikipedia.org/wiki/University_of_Cincinnatihttp://en.wikipedia.org/wiki/AODV#_note-0%23_note-0http://en.wikipedia.org/wiki/Unicasthttp://en.wikipedia.org/wiki/Multicasthttp://en.wikipedia.org/wiki/Distance-vector_routing_protocolhttp://en.wikipedia.org/wiki/DSDVhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Broadcasting_(computing)http://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Communications_protocol


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feature is that if a route re0uest fails% another route re0uest /a not be sent until twice as

/uch ti/e has passed as the ti/eout of the pre!ious route re0uest.

The ad!antage of A is that it creates no e1tra traffic for co//unication along

e1isting links. Also% distance !ector routing is si/ple% and doesn5t re0uire /uch /e/or

or calculation. 6owe!er A re0uires /ore ti/e to establish a connection% and the

initial co//unication to establish a route is hea!ier than so/e other approaches.

3or other alternati!es see theAd hoc routing protocol list.

Ad 6oc on-de/and distance !ector (A) routing protocol uses an on-de/and

approach for finding routes% that is% a route is established onl when it is re0uired b a

source node for trans/itting data packets. It e/plos destination se0uence nu/bers to

identif the /ost recent path. The /ajor difference between A and &" ste/s out

fro/ the fact that &" uses source routing in which a data packet carries the co/plete

path to be tra!ersed. 6owe!er% in A% the source node and the inter/ediate nodes

store the ne1t-hop infor/ation corresponding to each flow for data packet trans/ission.

In an on-de/and routing protocol% the source node floods the "oute"e0uest packet in the

network when a route is not a!ailable for the desired destination. It /a obtain /ultiple

routes to different destinations fro/ a single "oute"e0uest. The /ajor differencebetween A and other on-de/and routing protocols is that it uses a destination

se0uence nu/ber (est&e0Nu/) to deter/ine an up-to-date path to the destination. A

node updates its path infor/ation onl if the est&e0Nu/ of the current packet recei!ed

is greater than the last est&e0Nu/ stored at the node. A "oute"e0uest carries the

source identifier (&rcI)% the destination identifier (estI)% the source se0uence nu/ber

(&rc&e0Nu/)% the destination se0uence nu/ber (es&e0Nu/)% the broadcast identifier

('castI)% and the ti/e to li!e (TT7) field. est&e0Nu/ indicated the freshness of the

route that is accepted b the source. 2hen an inter/ediate node recei!es a "oute"e0uest%

it either forwards it or prepares a "oute"epl if it has a !alid route to the destination. The

!alidit of a route at the inter/ediate node is deter/ined b co/paring the se0uence

nu/ber at the inter/ediate node with the destination se0uence nu/ber in the

"oute"e0uest packet. If a "oute"e0uest is recei!ed /ultiple ti/es% which is indicated b
http://en.wikipedia.org/wiki/Ad_hoc_routing_protocol_listhttp://en.wikipedia.org/wiki/Ad_hoc_routing_protocol_listhttp://en.wikipedia.org/wiki/Ad_hoc_routing_protocol_list


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the 'castI-&rcI pair% the duplicate copies are discarded. All inter/ediate nodes ha!ing

!alid routes to the destination% or the destination node itself% are allowed to send

"oute"epl packets to the source. E!er inter/ediate node% while forwarding a

"oute"e0uest% enters the pre!ious node address and its 'castI. A ti/er is used to delete

this entr in case a "oute"epl is not recei!ed before the ti/er e1pires. This helps in

storing an acti!e path at the inter/ediate node as A does not e/plo source routing

of data packets. 2hen a node recei!es a "oute"epl packet% infor/ation about the

pre!ious node fro/ which the packet was recei!ed is also stored in order to forward the

data packet to this ne1t node as the ne1t hop toward the destination.

Advantages and Disadvantages

The /ain ad!antage of this protocol is that routes are established on de/and and

destination se0uence nu/bers are used to find the latest route to the destination. The

connection setup dela is less. ne of the disad!antages of this protocol is that

inter/ediate nodes can lead to inconsistent routes if the source se0uence nu/ber is !er

old and the inter/ediate nodes ha!e a higher but not the latest destination se0uence

nu/ber% thereb ha!ing stale entries. Also /ultiple "oute"epl packets in response to a

single "oute"e0uest packet can lead to hea! control o!erhead. Another disad!antage of

A is that the periodic beaconing leads to unnecessar bandwidth consu/ption.

ad-hoc on-demand distance vector

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