Centre for Wireless Communications Ad hoc On-demand Distance Vector Routing Protocol The presentation is based on a paper: C.E. Perkins, E.M. Royer, “Ad

Centre for Wireless Communications

Centre for Wireless Communications

Ad hoc On-demand Distance Vector Routing

Protocol

Ad hoc On-demand Distance Vector Routing

ProtocolThe presentation is based on a paper:

C.E. Perkins, E.M. Royer, “Ad hoc On-Demand Distance Vector Routing” Mobile Computing Systems and Applications, 1999.

Proceedings.WMCSA '99, 25-26 Feb. 1999

M.Sc. (EE) Jarmo Prokkola

University of Oulu, Telecommunication Laboratory & Centre for Wireless Communications

P.O. Box 4500 (Tutkijantie 2 E)FIN-90014 University of Oulu, Finland

[email protected], GSM: +358 40 706 1549

Telecommunication laboratory 27.01.2004

AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications

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Contents Introduction General information Basic functionality Path discovery Route tables Path maintenance Parameters of AODV The end discussion


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Introduction Ad hoc network is a self-organizing network

without centralized control, where each node acts as router to attain coverage over multiple hops.o Routing protocol has a very important role

Routing protocols have been studied widely and dozens of them have been presentedo Ad hoc On-demand Distance Vector (AODV) routing

protocol is considered in this presentation

Routing protocols

ReactiveProactive Hybrid

DSDV WRP

CGSR

AODV DSR LMR ABR LAR

TORA SSA

ZRP CBRP


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General Information Based on DSDV (Destination-Sequenced Distance

Vector) routing protocolo DSDV is effective in small networkso DSDV is ineffective in larger networks because of the

huge increase of control-information (of order n²)• Periodic update of the whole network topology

Reactive on-demand routing protocolo Route is formed only when neededo Pure on-demand route acquisition protocol

• No periodic routing table updateso More effective in larger networks=> Less control-information than in table-driven protocols

In principle, AODV is independent from lower layer functionalities as long as node’s can communicate with each other (basic connectivity).o Symmetric links (not strictly required)

Loop-free


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Basic Functionality Node has to be aware of the local connectivity

o Quick response time to local topology changes and route searches

o Local hello messages (a special form of RREP-packet)o Passive routing table update (i.e. listen to neighbor’s

transmissions) AODV relies on dynamically establishing route

table entries at intermediate nodes instead of source routing (e.g. DSR)o Packets do not carry the information of the whole

routeo Less control information

Fresh route information maintenance system is based on the method used in DSDVo Monotonically increasing route sequence numbers

are used to supersede stale cached routes


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Path discovery (1/5) Initiated, when node needs to

communicate with new node (no routing information in table)

Route Request (RREQ) packet is broadcasted to network

An expanding ring search should be usedo TTL (Time to live) parameter in IP-header sets

the lifetime in hops for packetso TTL is first small and is then increased, if a

route is not found until a limit is reached

source_addr source_seq_num

broadcast_id (RREQ_id)dest_addr dest_seq_num

hop_cntctrl_info

64 bits

192 bits

RR

EQ


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Path discovery (2/5) Example: Node A

needs to communicate with F

RREQ A->F is released to network

Neighbors C and B receive RREQ and learn route to A

A

B

C

D

E F

RREQ

RREQ


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Path discovery (3/5) Intermediate nodes C

and B do not have route to F

RREQ is broadcasted forward with increased hop count only if hop limit is not yet reached

A receives it’s own RREQo Reverse paths to B and C

are formedo RREQ is discarded

Intermediate node D receives multiple copies of RREQ form Ao Direct routes to C and B

are formedo The first arrived RREQ is

set used to form route to A

(e.g. B here)

A

B

C

D

EF


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Path discovery (4/5) D forwards RREQ B and C discard

duplicate RREQ and learn route to D

Destination node F finally gets RREQ

A

B

C

D

EF


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Path discovery (5/5) Route reply packet (RREP) is

sent back to node A along reverse routeo In fact any node, which has

a fresh route to destination can send RREP and therefore end route search

Active forward path from A to F is createdo Intermediate nodes also

have now active forward path to F

Route is ready for data transmission

A

B

C

D

E F

RREP

RREP

RREP

source_addr lifetimedest_addr dest_seq_num

hop_cntctrl_info

64 bits

160 bits

RR

EP


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Routing tables

A

B

C

D

E F

Dest Nex hop Num hops Exp time Seq num dest Active neighborsB B 1 10 sC C 1 3 sF B 3 20 s

Dest Nex hop Num hops Exp time Seq num dest Active neighborsA A 1 10 sD D 1 3 sF D 2 20 s

Dest Nex hop Num hops Exp time Seq num dest Active neighborsD D 1 10 sA D 3 10 s

Dest Nex hop Num hops Exp time Seq num dest Active neighborsC C 1 3 sE E 1 3 sA B 2 10 sB B 1 10 sF F 1 20 s

Route expiration times are updated when route is used Routes in AODV are in fact virtual routes!

o a single node do not know the complete route and therefore “route control” is distributed


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Path maintenance (original AODV)

Example: Link D<->F is broken due to movement of F

A special RREP is send upstream in path (now B->A)o hop_count to lost

destination (now F) is set to ∞

From RREP node A sees a broken link towards Fo New route is searched as in

initial route search (RREQ) if needed

A

B

C

D

E

F

F

RREP (lost node)

RREP (lost node)

lost link

RREP (lost node)

RREP (lost node)


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Path maintenance (AODV, July 2003)

If a link is broken, route repair is initiated (if active)o Link failure detecting node initiates

route search (Now, RREQ D->F) Route Error (RERR) is generated if

repair is failed or deactivatedo All the routes concerning the lost

link will be written to RERRo Entries of the unreachable nodes

are invalidated o A DELETE_PERIOD is set to indicate

final elimination of the route table entry

o RERR is send to all nodes affected by the link breakage

A new route to known node is accepted if route’s sequence number is greater than the number of old routeo If hop count of a new route is

greater, it is up to source node to decide what to do (RERR-notification is sent)

A

B

C

D

E

F

F

RREQ

RREQ

RREP

RREP

RREQ RREQ


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About AODV parametersParameter name Default value (description)

ACTIVE_ROUTE_TIMEOUT 3 (The timeout for route expiration) ALLOWED_HELLO_LOSS 2 HELLO_INTERVAL 1 (The interarrival time of hello-messages)BLACKLIST_TIMEOUT RREQ_RETRIES * NET_TRAVERSAL_TIMEDELETE_PERIOD depends on the link-layer (delete-timeout for route

entry)LOCAL_ADD_TTL 2MAX_REPAIR_TTL 0.3 * NET_DIAMETER MIN_REPAIR_TTL should be at least the last known hop count to

destinationMY_ROUTE_TIMEOUT 2 * ACTIVE_ROUTE_TIMEOUTNET_DIAMETER 35 (the maximum number of hops between two nodes)NET_TRAVERSAL_TIME 2 * NODE_TRAVERSAL_TIME * NET_DIAMETERNEXT_HOP_WAIT NODE_TRAVERSAL_TIME + 10 sNODE_TRAVERSAL_TIME (Conservative estimate of the 1 hop packet delay)PATH_DISCOVERY_TIME 2 * NET_TRAVERSAL_TIMERERR_RATELIMIT 10RING_TRAVERSAL_TIME 2*NODE_TRAVERSAL_TIME * (TTL_VALUE+TIMEOUT_BUFFER)RREQ_RETRIES 2RREQ_RATELIMIT 10TIMEOUT_BUFFER 2TTL_START 1TTL_INCREMENT 2TTL_THERESHOLD 7TTL_VALUE (the TTL in packet header in operation)


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Properties of AODV Performs generally well in most cases

o Adapts easily to changing environment (mobility)o The amount of control-information is reducedo With pure on-demand nature, it enables huge

networks Has been studied widely and the development

of the protocol is in rather advanced state Is easy to implement over different lower layers Does not require anything else but a possibility

to communicate with neighbors Difficult to be adapted with changing traffic load

because of numerous parameters, even though the protocol itself is quite simple

Often used as a comparison point for other routing protocols

Documents

Centre for Wireless Communications Ad hoc On-demand Distance Vector Routing Protocol The presentation is based on a paper: C.E. Perkins, E.M. Royer, “Ad