A Performance Comparision of Multi-Hop Wireless Ad Hoc Networking Routing Protocols

There are several choices to be made in constructing ad-hoc routing protocols, several of which are explored by the protocols in this paper:

• route construction time — on demand (AODV, DSR, TORA) or always (DSDV)
  
• loop avoidance mechanism — sequence number (DSDV, AODV), source routing (DSR), topological ordering + drop packets during link reversal (temporary routing loop) (TORA)
  
• route storage — next hop table (DSDV, AODV), topological ordering (“height”) (TORA), at source/on data packets (DSR)
  

Additionally, these algorithms need to choose various timeouts and rates and delays (to avoid accidental synchronization) for link state and route discovery messages as well as route propagation policies.

The authors of this paper implemented DSDV (with two different route propagation policies), AODV (with explicit beacons and with on-send loss detection), DSR, TORA in a detailed simulation of a 802.11 network with RTS/CTS. They choose several simulations scenarios with varying degrees of mobility (both in speed and movement frequencies) randomly in the simulated space. They used several fixed-rate packet sources (between 10, 20, or 30 random pairs of hosts) with sufficiently small packet sizes to usually avoid congestion losses. Given these scenarios, they measured the delivery rate, routing overhead (in bytes and packets), and route length versus the optimal path.

They found that routing protocol efficiency greatly depended upon the degree of mobility: faster, more frequent movement resulted in substantially larger overheads for all but DSDV. Except for TORA at high packet rates (where it experienced a routing protocol congestion collapse) and DSDV with high mobility (where its periodic updates were not fast enough), performance was good overall: more than 95% of packets were delivered and most packets took the shortest route. In terms of routing overhead, results were not surprising (except for TORA, which seems to be clearly broken), demand routing protocols (except for TORA) did substantially better and DSR seemed to trade off increased byte usage for decreased packet usage.

It's good to see a careful simulation of these various routing protocols under enough circumstances that it should be difficult to claim that an advantageous situation has been missed. Of course, the downside of a big sensitivity analysis like this is that reading the paper, I can't really tell how the choice of protocol would matter for a realistic application of an ad-hoc network. Except for the obviously bad cases (e.g. most of TORA, DSDV with very high mobility), would these differences (in overheads, delivery rates) even have a substantial effect on application performance?