06-08-2014, 12:13 PM
ODMRP
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Introduction
Issues in Ad Hoc Networks
Bandwidth Constraints
Frequent Topology changes
Limited Battery power
Problems with Current Multicast Routing Protocols
They have a tree based structure, so as the node connectivity changes, the tree structures changes accordingly.
Multicast trees require a global routing substructure
involving excessive channel and processing overhead
ODMRP
Provides a richer connectivity among multicast members using a mesh based approach
Supplies multiple route for one particular destination
Helps in case of topology changes and node failure
Uses a concept of Forwarding Group
Only a subset of nodes forwards multicast packets via scoped flooding
Data Forwarding
A node forwards the received multicast data packet only when it is not a duplicate one and the setting of FG_FLAG for that multicast group has not expired.
Soft state
No explicit control packet need to be sent to join or leave a group.
If a multicast source wants to leave a group, it simply stops sending the JOIN QUERY packets.
If a receiver o longer wants to receive from a multicast group it does not send the JOIN REPLY for that group.
Forwarding nodes are demoted to non-forwarding nodes if not refreshed( no Join Replies received) before they timeout.
Unicast Capability
It can operate as an unicast routing protocol also as well as coexist with any unicast routing protocol.
Adapting the Refresh Interval via Mobility Prediction
Periodic flooding of Join query to refresh routes and group membership is not a good idea due to bandwidth constraints.
Enhancing the performance of ODMRP demands selection of an optimal route interval .
GPS (Global positioning system) provides location and mobility information of a node. Thus Join Queries can be sent only when route breaks of ongoing data session are imminent.
In the paper, assumption is made that the clocks are synchronized by NTP or GPS itself at boot time.
By the knowledge of speed, direction and radio propagation range, one can determine how long a node will remain connected.
Conclusion
Features of ODMRP :
Simplicity
Low channel and storage overhead
Usage of Up-to-date shortest routes
Reliable construction of routes and forwarding group
Robustness to host mobility
Maintenance and utilization of multiple paths
Exploitation of the broadcast nature of the wireless environment
Unicast routing capability
Area to be looked into:
ODMRP has a problem of excessive flooding when number of multicast senders are more.
One solution to this is to make the route refresh as receiver initiated or one can make ODMRP adaptive to the way the network changes.