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RFC 3561 AODV Routing Protocol

RFC 3561 AODV Routing Protocol

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RFC 3561 AODV Routing Protocol

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  1. RFC 3561 AODV Routing Protocol Mobile Ad Hoc Networking Working Group Charles E. Perkins INTERNET DRAFT Nokia Research Center 19 June 2002 Elizabeth M. Belding-Royer University of California, Santa Barbara Samir R. Das University of Cincinnati 資料來源:draft-ietf-manet-aodv-11.txt 報告人:吳政鴻 日期:2005/2/29

  2. What an ad-hoc routing protocol needs • Multi-hop paths • Self-starting • Dynamic topology maintenance • Loop-free • Low consumption of memory, bandwidth • Scalable to large node populations • Localized effect of link breakage • Minimal overhead for data transmission • Rapid convergence

  3. AODV: Ad-Hoc On-Demand Distance Vector Routing • Quick loop-free convergence • Route creation on demand, localizing the effect of topology changes, and minimizing control traffic. • Distance Vector, using Destination Sequence numbers for route updates (on both forward and reverse paths) • Triggered updates and minimal latency for route replies • two-dim'l metric: <seq#, hop-count>

  4. A destination node increments its own sequence number in two circumstances: • before a node originates a route discovery • before a destination node originates a RREP in response to a RREQ

  5. AODV route table entry • Destination IP Address • Destination Sequence Number • Vaild Destination Sequence Number flag • Network Interface • Hop Count (number of hops needed to reach destination) • Next Hop • List of Precursors • Lifetime (expiration or deletion time of the route) • Other State and routing flag (e.g. valid, invalid, repairable, being repaired)

  6. A node may change the sequence number in the routing table entry • it is itself the destination node, and offers a new route to itself • it receives an AODV message with new information about the sequence number for a destination node • the path towards the destination node expires or breaks

  7. The route is only updated ifthe new sequence number • higher than the destination sequence number in the route table • the sequence numbers are equal, but the hop count is smaller than the existing hop count in the routing table • the sequence number is unknown

  8. AODV Unicast Route Discovery • RREQ (route request) is broadcast • Reverse path is set up along the way • RREQ message contains < bcast_id; dest_ip; dest_seqno;src_ip; src_seqno; hop_count > • RREP (route reply) is unicast back • From destination if necessary • From intermediate node if that node has a recent route

  9. AODV Route Discovery Time Out Time Out : RREQ : RREP :Valid Route

  10. AODV Local Route Repair : RREQ : RREP :Valid Route Data packet be buffered

  11. : RREQ : RREP :Valid Route :RERR Data packet be buffered Data packet be discarded

  12. Route Request (RREQ) Message Format

  13. Route Reply (RREP) Message Format

  14. Route Error (RERR) Message Format

  15. Link Breakage • Nodes remember active routes • Next hop breaks ­> neighbors using that route are notified • Notification is a RREP with: - metric = ∞ - dest_seqno = previous + 1 and is sent to each active neighbor

  16. Ad-hoc Networking Example • Suppose MH1 moves away from MH2 towards MH7, and has active sessions with MH3 and MH6. The following actions occur:

  17. MH2 notices that its link to MH1 is broken • MH2 checks its routing table, and finds that its link to MH1 was actively in use by MH3 and MH4. • MH2 unicasts an ∞-metric route update, with an incremented destination sequence number, to MH3 and MH4. MH3 may subsequently issue a new route request for MH1. • MH4 also notes that its route to MH1 was actively in use, and forwards the ∞-metric route update to MH6. • MH6 may subsequently issue a new route request for MH1.

  18. Conclusions • AODV has the following features: - Nodes store only the routes that are needed - Need for broadcast is minimized - Reduces memory requirements and needless duplications - Quick response to link breakage in active routes - Loop-free routes maintained by use of destination sequence numbers - Scalable to large populations of nodes.