## 7 Discussion  
Reactive routing protocols rely on flooding, as part of their route discovery process. In wireless networks, flooding incurs the risk of on-the-media collisions and resulting data losses, with the use of  
Figure 18: Simulation results of shortest-delay RREQ forwarding. (**a**) The number of collisions; (**b**) The average route discovery delay; (**c**) Average path length. jitter on packet (re-)transmissions being the remedy commonly employed for alleviating these losses. The performance of the flooding operation has, as this paper has presented, a direct impact on the quality of the routes discovered. A similar conclusion was found in [25], in which not jitter, but different flooding algorithms were compared for their impact on route quality when used as part of the route discovery process of a reactive routing protocol. For the purpose of route discovery, the performance of a flooding operation can be evaluated through three main criteria: (1) the resulting quality (path lengths) of discovered routes; (2) the delay incurred when discovering a new route; and (3) the number of collisions caused by route request flooding. Collisions and route quality have a direct impact on the network load: packet collisions may lead to retransmissions, longer paths imply that more transmissions happen than would otherwise be required between a source and a destination. Alas, with respect to jitter, it is not possible to optimize a flooding operation according to all criteria: an infinitely large jitter interval might, for example, eliminate collisions, but would incur unacceptable delays before routes were established. This section summarizes the trade-offs achieved by the different mechanisms proposed and evaluated in this paper. It is well established that pure flooding (_i.e._, without jitter) in wireless multi-hop networks entails an unacceptable level of packet collisions. The use of \"standard jitter\" (_i.e._, uniform jitter according to RFC 5148 [9] distributed within \([0,J_{m}]\)) reduces the amount of flooding collisions, at the expense of: (1) slowing down the flooding process; and (2) causing the \"delay inversion\" effect, as described in Section 3. According to the analysis of Section 4, delay inversion does not depend on the length of jittering time interval (\(J_{m}\)) and becomes more relevant in long paths; that is, in big-diameter networks. Window jitter introduces a minimum non-zero pre-forwarding delay (\(\alpha J_{m}\)). This dramatically reduces the probability that delay inversion occurs, and thereby an improvement of the quality of discovered routes (in the shortest-delay mode) or a reduction in control overhead and packet collisions (in the shortest-path mode). It also increases the number of collisions in the first hop of flooding of the flooding process (_i.e._, when an RREQ is retransmitted by routers one hop away from the source), as jitter selection becomes more deterministic. Further evaluation of the performance of RREQ flooding, with \"standard\" jitter and window jitter, via graph and network simulations (Sections 5 and 6), provide empirical evidence of the route quality improvement with window jitter and shows that the number of collisions along the explored paths is also reduced with this mechanism. Additional collisions in the first hop are thus largely compensated for by the reduction in the number of transmissions farther away; an effect that becomes relevant as the network density increases. Figure 19 provides a qualitative representation of the different trade-offs achieved by the three main variants (no jitter, uniform and window jitter). Window jitter outperforms standard jitter in hop count networks, but performs poorly when link quality values are heterogeneous. In scenarios in which link quality information is available across the network (for instance, via link quality estimation), adaptive jitter presents clear advantages with respect to the two static configurations (standard and window jitter).