ODMRP-ASYM (On Demand Multicast Routing Protocol) For Linux Implementation

This paper presents our work with an ODMRP (on demand multicast Routing Protocol) to extend its functionality to work with asymmetric links in a Linux Environment. We were given the functional code for the ODMRP protocol, as well as a test-bed to work with which consisted of five Dell Lattitude laptops equipped with Lucent Wireless PCMCIA 802.11 cards. Our implementation consists of adding to the existing ODMRP code two packet definition types, as well as handlers for these packet types. The packet types are the new Loop Discovery Packet and Loop Marking Packet. These are used to detect loops in order to solve the asymmetric link problem in routing. This is done in the reply phase of the path discovery for ODMRP. When the node sending the Join Table Packet times out while waiting for an acknowledgement, the Loop Discovery Packet is then transmitted from that node. This packet goes around the loop collecting IP addresses of the nodes in the loop, and when the node that timed out sees this packet again, the loop has been discovered. That node then sends out the Loop Marking Packet, which marks all the nodes in that loop as forwarding nodes. Through this procedure, the forwarding group is created even with asymmetric links, and the sending node is able to have an established path to the receiving node. Much of the difficulty of this implementation was in the configuration of the test-bed to be able to enable the laptops to communicate correctly with each other.