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:

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 if the 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  RREP (route reply) is unicast back From destination if necessary From intermediate node if that node has a recent route

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

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.