ODMRP Enhancement

Multicasting in ad hoc nets ODMRP: On Demand Multicast Routing Protocol Most widely accepted ad hoc multicast routing protocol Simple yet high-performing Why multicast in ad hoc nets? Group (1-to-many) communication Wireless “broadcast” medium Spectral efficiency

ODMRP: Initialization Phase Join Query Join Reply Forwarding Node Link Multicast Route On-demand approach: A source initiates Join Query only when it has data to send The sender periodically floods Join Query control messages All intermediate nodes set up route to sender (backward pointer) Members send Join Reply message Routes from sources to receivers build a mesh of nodes called “forwarding group”. Forwarding Group S1 R S R S2 R R

ODMRP: operation No explicit join/leave messages Source broadcasts data packet to neighbors The Forwarding Group neighbors forward the M-cast packet via “restricted” flooding on the forwarding mesh Soft state No explicit join/leave messages Forwarding nodes clear state upon timeout Extremely robust to mobility Forwarding Group R S R S2 R R

ODMRP Performance - PDR

Simulation result – O/H

ODMRP Soft-state Pros/Cons Advantage Simple Frequent refresh helps overcoming node displacements and channel fading Keep shortest path Disadvantage Too much overhead when low mobility

Enhancing ODMRP Adaptive route refresh rate Semi soft state: Explicit join + timeout Local route recovery

Enhancing ODMRP Explicit join A node that wants to join multicast group starts expanded ring search to find a member or forwarder The node connects with any node in multicast group with 3 step hand-shaking A node does not need to wait next route refresh from the source We can change refresh interval

Enhancing ODMRP Cont. Expanding Ring Search A node broadcasts packet with increasing TTL If TTL is too large, it may generate control packet overhead so we need maximum TTL when ring search Maximum TTL in ring search is 3~5 since the node is still near the ODMRP mesh when the route is broken with mobility. Reach maximum TTL, the node broadcasts Join Query Request packet. When the source receives this packet, it sends Join Query for route refresh

Enhancing ODMRP Cont. Local Route Recovery Each node stores the longest data packet arrival interval that the source node sends with Join Query packet. If nodes do not receive any data during 2*packet arrival interval, they start route recovery When nodes recognize route breakage, they start route recovery Process is the same to explicit join

Enhancing ODMRP Cont. Route Refresh Interval The source sends Join Query every 30 second (Odmrp is 3 second) The source sends Join Query when it receives Join Query Request packet from any member node.

Simulation result - Packet Delivery Rate 1 sources, 20 members, and total 50 nodes with various mobility ODMRP and Enhanced ODMRP similar performance

Simulation result - Control Packet Overhead 1 sources, 20 members, and total 50 nodes with various speed

Unidirectional Link: Characteristics and Problems link that connects A to B, but not B to A Sources of asymmetry External interference Transmission power control Directional antennas Unidirectional link problem in on-demand routing Reverse Path technique does not work. A B

ODMRP-ASYM FACT: A loop must exist if the network is connected (ie, there are two unidirectional paths between a pair of nodes). Our strategy: Discover the loop and use it! Path from S to D S A B Loop! Unidirectional links E C D Path from D to S

ODMRP with unidirectional links Source S floods Join Query toward D Reverse path to relay Join Reply from D to S is blocked at B due to link asymmetry Join Query S A B F E C D Join Reply

ODMRP-ASYM: Loop Discovery On detecting asymmetric link, node B initiates Loop Discovery Packet (LDP) flooding LDP goes around the loop while collecting node IDs in the loop and returns to B LDP LDP S A B CEA E C D

Simulation QualNet Two-power-level model: two different tx power levels are assigned to nodes randomly 50 nodes, 1 source, 1 group with 10 members Traffic: CBR, 4 packets/sec, 512 bytes/packet Varying density by changing field size: 1500 x 1500 m2 ~ 3500 x 3500 m2 Mobility model: Random waypoint

Simulation results: Packet Delivery Ratio Figure 1: Packet Delivery Ratios (mobile nodes with max speed = 20m/s and pause time = 15s) Figure 2: Packet Delivery Ratios (static nodes)