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Ad Hoc Networking with AODV
Charles E. Perkins
Nokia Research Center
Mountain View, CA USA
http://people.nokia.net/charliep
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Outline of Presentation
• Ad Hoc Networks in general
• AODV in particular
• Recent results from manet
• Internet Gateways for ad hoc networks
• Address autoconfiguration
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Ad Hoc Network characteristics
• peer-to-peer
• multihop
• dynamic
• zero-administration
• low power
• autonomous
• autoconfigured
But, most of these have exceptions!Idea: let (?almost?) every node be a router
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Commercial (or not!) Opportunities
• Conferencing
• Home networking
• Range extension for cellular base stations
• Emergency services• Ambulance• Police
• Hospitals
• Embedded computing applications• Ubiquitous computers with short-range interactions• Automotive/PC interaction
• Enable computing where subnets do not exist
• Jungle telemetry
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Technical/Market/Political hurdles
• Scalability (memory search time, bandwidth, processing)
• Power budget vs. latency
• Protocol deployment, incompatible standards
• Why should one node “waste power'' to help a neighbor ?
• Wireless data rates
• Obsoletes the client/server model... breaks a lot of protocols
• User education, acculturation
• Antenna inconvenience (not anymore, really)
• Higher bit-error-rate (BER)
• Additional security exposure
• Non-ubiquitous coverage
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On-Demand Routing Protocols
• Eliminate route table updates for routes that are not used
• Fewer control packets: better scalability, reduced congestion, better
robustness reduced processing requirement
• Even more localization for topology changes if distance vector
• Also can be made to work for (partial) link state• or, better, hybridized distance vector and link state
• Downsides:• Latency• Route Discovery broadcasts• ICMP Unreachable only after Route Discovery attempt
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Mobile Ad Hoc Networking (manet)/ AODV
• AODV: on-demand, and distance vector• Route caching & timeout offers improvement over
others• Proved “correct”• Interoperability testing, and (soon?!) Experimental RFC
status
• AODV uses network-wide RREQ, unicast RREP along reverse path to source of the request.
• DSR uses similar route discovery, maintains source routes
• OLSR and TBRPF are link state, proactive protocols
• Active discussion about Internet Gateways
• Address Autoconfiguration
• Reducing retransmissions for system-wide flooding
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AODV Features
• Reactive routing protocol; route discovery cycle for route finding
• Route repairs and TTL restrictions reduce network-wide flooding
• Maintenance of active routes• Loop freedom achieved through sequence numbers• No overhead on data packets• Scalability shown to 10,000 nodes
• performance suffers• Integrated multicast protocol (MAODV) specified
• multiple next hops• group leader maintains sequence number
• QoS extension specified (undergoing revision)• AODV for IPv6 is specified, built, and works
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AODV Unicast Route Discovery Initiation
Route Request (RREQ) broadcast flood
Source
Destination
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AODV Unicast Route Discovery Completion
Route Reply (RREP) propagation
Destination
Source
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Internet Gateways for Ad Hoc Networks
• Our model: do not inject per-host routes into Internet
• Good start: ad hoc nodes use gateway as default router• but it could be multiple hops away• plus, the ad hoc nodes need to know its IP address• router solicitation/advertisement “work”, with changes
• Gateway should be “protocol-agnostic” (for any manet protocol)
• Gateway needs a host route for each manet node
Gateway
Entry node
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Address Autoconfiguration
• Node discovers Internet-routable prefix from Internet Gateway, if any
• Otherwise, use canonical site-local address
• Required: some variety of Duplicate Address Detection (DAD)
• For connected networks, RREQ/RREP does the job• tricky part: what is the source address?• have specified AREQ and AREP for “general” case (should
work with protocols other than AODV)
• The hard part: dealing with network merge or healing
Gateway
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Ad Hoc Networking Research
• MobiHoc (ACM SIGMOBILE) (plus quite a few others!)• Third conference held in June – 150 papers submitted
• Active research areas (a few among many!)• Inherent capacity bounds?• Better Routing• Automotive (“parallel” one-dimensional networks?)• Backbones, Clustering• Power control• Simulations seem quite untrusted
• AODVng• Gray zones (interference range vs. signal range;
HELLO nonworking)• QoS/Diffserv/”no free lunch”• Security (!!)• Implementer’s mailing list• Multipath• AODVjr.
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Summary and Conclusions
• Ad Hoc Networking is well-established as a viable research area
• Infrastructureless operation has many applications
• On-demand protocols offer many advantages
• AODV makes use of advantages from both Distance-Vector and On-demand
• AODV has good chances for standardization
• Ad hoc networks can be glued to the Internet and then provide wireless extension domains
• Address autoconfiguration techniques have been adapted
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Various Ad Hoc Routing Projects
• DSR (Dave Johnson, CMU)
• WINGs (JJ Garcia/UCSC)
• ROAM (JJ Garcia/UCSC)
• WAMIS (Gerla/UCLA)
• ODMRP (Gerla et.al/UCLA)
• TRAVLR (Kleinrock/UCLA)
• Tora/IMEP (Park, Corson/UMD)
• Link Quality (Rohit Dube/UMD)
• LAR (Texas A&M)
• TBRPF (SRI)
• OLSR (Inria: Clausen./Jacquet)
• DSDV (Dest. Sequence #'s)
• AODV (refinement of DSDV)
• AOMDV (Multipath – Das/Marina)
• Hierarchical (Akyildiz/Georgia Tech)
• GPSR (Karp/Harvard)
• CBRP (Singapore)
• Terminodes (EPFL)
• MMWN (Steenstrup/BBN)
• ABR (C.K. Toh)
• STAR (JJ Garcia/UCSC)
• ZRP (Zygmunt Haas/Cornell)
• Fisheye/Hierarchical (UCLA)
• CEDAR (Urbana-Champaign)
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Distance Vector Routing Protocols
• Route table has (metric, next hop) – i.e., (distance, vector).
• Other metrics (e.g., time) may be more useful in many cases
• “Distributed Bellman-Ford” algorithms
• Can be made loop-free
• Easy to program
• Low memory and processor utilization
• Localized update operations (important for ad hoc)
• Susceptible to counting-to-infinity problem
• Previous solutions (poison reverse/split-horizon) must be undone
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