Draft Notes 1 : Scaling in Ad hoc Routing Protocols

As a simple example, consider flooding. In flooding a source broadcasts a data packet along with a unique identifier (UID). This UID is used by every receiver to check if it has already heard this packet before or not. If not the receiver broadcasts the packet. In this way the data packet is eventually transmitted by every node in the network, except the receiver. How might we get a UID? The UID might be the source address and a distinct number assigned by that source. Flooding is simple in that it implicitly discovers the network topology, forming a tree of transmissions starting at the source and branching out to the other nodes in the network. It is robust since the message is repeated by many nodes in the network and thus a lost reception may not be significant if the receiver gets the packet from other nodes in the broadcast. The route choice is also implicit in that the packet follows all paths along the flooding tree. Route maintenance is also robust in the sense that it uses whatever connectivity exists at the time of the flood and assumes nothing based on prior floods. Flooding is a simple and robust protocol and so is a baseline against which to compare other protocols. How do we compare with other protocols? There might be several metrics related to packet delay, packet delivery ratio, and routing overhead. Delay might measure how much excess time it takes to deliver the data packet compared to the minimum time assuming the routing follows the shortest path. Packet delivery ratio is the ratio of packets