Routing Protocols

This paper compares several protocols: DSDV, TORA, DSR, and AODV. Another pair of papers I should have read in the opposite order. Anyway, the metrics it uses are the percentage of packets that get through, overhead introduced by the routing protocol (in number of packets), and path optimality (difference between length of chosen path and minimum length of path). It uses a simulation in which nodes move around a rectangular area at random speeds, with a variety of predetermined rest-times. These rest times range from 0 to 900 seconds (continuous motion to no motion). Furthermore, this is the first paper to gather metrics while multiple transmitters are sending data (10, 20, or 30).

First, a bit about the algorithms. DSDV (Destination Sequenced Distance Vector) is an algorithm in which each node maintains data about the next hop for each destination. Nodes regularly broadcast updates to eachother whenever the network topology changes. These broadcasts include sequence numbers, allowing other nodes to choose the most recent updates.

All other routing protocols are based on dynamic requests for routes. TORA (Temporally Ordered Routing Algorithm) responds to requests by attempting to compute the "height" of each node with respect to the destination, and then sending an update back to the requester. DSR (Dynamic Source Routing) works by simply asking for a route, and then allowing the entirety of the found route to be propagated backwards through updates. AODV (Ad hoc On demand Distance Vector) is essentially a combination of the DSR and DSDV algorithms. It keeps the same state as DSDV, but its updates are done by request-update, instead of periodic pushes.

In summary, All algorithms get approximately the same throughput across different rest times, except for DSDV, which cannot make its paths converge for small rest times. However, the overhead (in number of packets) of DSR is the smallest. The overhead of AODV is smaller in bytes than the overhead of DSR, but those bytes are distributed across many small packets. Most overheads decrease as rest time increases, with the exception of DSDV, which remains constant. Despite this, DSDV does second-best in path optimality, next to DSR.