Multicast Operation of the Ad-Hoc On-Demand Distance Vector Routing Protocol

Royer, Perkins

network routing multicast aodv maodv

@inproceedings{royer:mobicom-1999,
  author={Royer, Elizabeth M. and Perkins, Charles E.},
  title={Multicast Operation of the Ad-Hoc On-Demand
         Distance Vector Routing Protocol},
 booktitle={{ACM}/{IEEE} International Conference on
            Mobile Computing and Networking ({Mobicom})},
 year={1999},
 pages={207--218},
 publisher={ACM},
} 

No single point of failure

Constructs trees as needed

Source IP and Identification number identify packets

Leverage topology information gained in unicast and multicast routing together

Assumes symmetric links

Multicast group leader maintains multicast group sequence number

Nodes send RREQs when they want to join group, or have data to send to group

When a node joins a group:

• If it has a record of the group leader, it sends the RREQ to them
• Otherwise the RREQ gets broadcast

Members of the group tree respond to the RREQ

Nodes tries a number of times to contact group leader

• If they fail, self-elects to be group leader

Prominent among these is Multicast Ad Hoc On-Demand Distance Vector (MAODV)~\cite{royer:mobicom-1999}, which directly applies principles of and incorporates into the Ad Hoc On-Demand Distance Vector (AODV) unicast protocol~\cite{perkins:wmcsa-1999}. MAODV constructs group shared trees on demand when requested by group members or message sources. Nodes that wish to join a group or send data to it construct and locally broadcast a route request message. Any current member of the multicast tree that receives such a request replies. If a non-member of the group that knows a current path to the group receives a route reuest, it replies if the request is not a join. Otherwise, the request is forwarded on by receiving nodes, eventually propagating across the entire network, with the each node storing the previous request forwarder as their next hop back to the source.

Replies from group members or informed nodes are then unicast back to the originating source using that reverse path information. The source will thus receive multiple responses to its route request. Among these it chooses the shortest path with the most fresh routing information, determined by a group sequence number controlled by the group leader. If the node is joining the group, it issues a multicast activation message, which is propagated to the current group and enables forwarding of group traffic on that path, extending the tree.

If several route requests go unanswered, the node may assume no other group members exist or are reachable. It then elects itself group leader and begins to respond to requests, establishing the multicast group tree around itself. Tree maintenance is conducted via timeouts on group traffic, with lulls filled in by keep-alive messages. Failed timeouts alert children that their parent has become disconnected, and they re-initiate the join process.