ExOR: Opportunistic Multi-Hop routing for wireless Networks

ExOR proposes a integrated routing and MAC protocol. The basic mechanism introduced is to use the inherit broadcast property of wireless links to broadcast a packet to multiple receivers. Once we know the receivers that actually received the packet, then based on the location of the receiver from the destination, we choose the best receiver to forward the packet. This effectively delays the forwarding decision until after the transmission of the packet. In the paper it mentions 4 key challenges. First, only a subset of nodes should receive the packet. Since there needs to be some sort of communication between the nodes to determine the best fit forwarder, the more nodes that receive the packet, the more communication overhead there will be. Thus, there needs to be a small yet effective set of nodes that receive the broadcast. Secondly, the metric used to determine which node forwards the packet needs to be well designed, and we need ot make sure that one and only one node forwards the packet. Third, similar to the first point, only a subset of useful nodes should receive the packet. Finally, ExOR must avoid simultaneous tranmission to minimize collisions. The results looked decent, giving on average a 2 to 4 times gain on the throughput.

Both the papers we read seems to rely on the fact that all nodes can openly see the packets being transmitted. Conceptually we can almost think of this like a bus, where only one sender can send at a time and all receivers can see if the packet is destined for them. So it seems like broadcasting is one of the essential features of improving throughput now. But with ExOR, one major concern is its compatibility with TCP. The results they obtained was not directly layering ExOR over TCP, they used a split way proxy, and only the connection between 2 proxy points were using ExOR, thus the deployment of this seems to need more improvement in terms of compatability with TCP.