ad hoc on-demand distance vector routing protocol
DESCRIPTION
Ad hoc On-demand Distance Vector Routing Protocol. The 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 - PowerPoint PPT PresentationTRANSCRIPT
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
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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)
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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)
AODV Routing ProtocolM.Sc. (EE) Jarmo Prokkola 27.01.2004University of Oulu, Centre for Wireless Communications
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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