Monday, March 5, 2007

Caching Strategies in On-Demand Routing Protocols for Wireless Ad Hoc Ne

Caching Strategies in On-Demand Routing Protocols for Wireless Ad Hoc Networks, Yih-Chun Hu, David B. Johnson, in MOBICOM 2000, Boston, MA, pp. 231-42.

This paper proves that analytical modeling in ad-hoc network research is way overrated: there is not a single complicated mathematical equation. Even the study of correlation between different metrics seems to be done by observation rather than using sophisticated statistical tools. Yet, the paper does present a pretty compelling picture of different cache strategies. And rather than struggling to define an analytical model and then show it is valid, it cuts the middle-man and shows right away the impact of different parameters using extensive simulation.

The simulation is of course the main part: it is the CMU extension of the NS-2 simulator, which was designed by the group of this paper, and which was designed to produce results like this one. It is still the de facto standard for wireless mesh network simulation (it has been integrated in NS-2 distribution now) so this is as much part of the legacy of this group as the actual results presented in the paper.

The cache strategies studied are: unlimited cache size, or finite cache size with different sizes, or different ways of caching depending on who issues the node, or different ways of updating the cache (FIFO or not).

The paper finds a better value of the active time-out of the cached routes (the previous paper below would tell you it is velocity dependent, but here they seem to agree on a 5s value for most mobility models). It also shows that the larger cache study is not necessarily good, as it means more broken routes are being carried around, which leads to suboptimal performance.

I enjoyed the "omniscient expiration" concept (the strategy which keeps the route as long as it is valid), and will use it in a future paper.

The link to the monarch project: here.

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