## 8 Conclusions  
Jitter is used for message flooding in wireless multi-hop networks, in order to avoid data losses. It has been shown to be an efficient remedy in proactive routing protocols, such as OLSR [10], and has been recommended for general use by the IETF in RFC 5148 [9].  
However, when applied to the route discovery process in reactive routing protocols, using the jitter mechanism prescribed by RFC 5148 [9] has several undesirable side-effects. Observed experimentally, this paper identifies and quantifies analytically the \"delay inversion\", which may result in unnecessary control traffic overhead being generated and suboptimal paths to the destination ultimately produced.  
Not using jitter is not an option: route discovery relies on the flooding of RREQs, and with intermediate routers immediately retransmitting a received RREQ, collisions will still occur and (RREQ) packets will be lost. Therefore, this paper explores ways to employ jitter on RREQ flooding for reactive routing protocols, while minimizing the impact of delay inversion. In particular, window jitter and adaptive jitter, are compared to \"standard\" jitter (_i.e._, jitter according to [9]); and, of course, to naive flooding (_i.e._, immediate retransmission without jittering). This is not only in terms of incurred delay, but also in terms of avoided collisions, control overhead and quality of discovered routes. Comparisons have been performed by way of both probabilistic analysis and experimental analysis through graph and network (NS2)-based simulations.  
The proposed \"adaptive jitter\" is a simple modification to \"standard\" jitter, yet despite this simplicity, is able to, very substantially, reduce the probability of experiencing the effect of delay inversion, manifested by sub-optimal routes resulting from the route discovery process. In its most general version, it simply consists of sending flooded messages sooner across better links, which entails a higher probability of the route discovery process resulting in optimal routes. This paper also details the impact of jitter parameters and distribution, on flooding and route discovery performance. Depending on the characteristics of the network, the information available to the routers and the specific route discovery  
Figure 19: Comparative diagram between no jitter (circle), uniform or standard jitter (square) and window jitter (triangle).  
mode, different trade-offs between the main involved parameters (control overhead, route optimality, flooding delay) can be achieved with the proposed jitter distributions.  
The results, pretended in this paper, indicate that window jitter (and adaptive jitter, if routers can reliably estimate wireless link quality) is particularly beneficial for reducing overhead in dense networks, in which packet collisions are more frequent and, therefore, delay inversion more likely to happen, due to the the diversity of available paths. These jitter mechanisms thus are interesting for large resource constrained networks, such as in battery-powered mesh and sensor networks, where extraneous transmissions and long paths are particularly harmful to the network lifetime. Future work should see to confirm these results, both through additional analysis, more complex network simulations and real-world experiments. In particular, future work should study the impact of router mobility and wireless channel unreliability on the applicability of window and adaptive jitter.  
[PERSON] discovered the issue of the delay inversion effect in reactive protocols, proposed the adaptive jitter mechanism to alleviate the impacts and conducted the network simulations. [PERSON] built the analytical model of the jitter mechanisms and designed and performed the graph simulations. [PERSON] provided important contributions to the study of uniform jitter and reactive routing protocols.