http://blogs.sanmathi.org/nalanda/2008/10/08/exor-opportunistic-multi-hop-routing-for-wireless-networks/ Just another WordPress weblog Sat, 19 May 2012 10:19:50 +0000 http://wordpress.org/?v=2.6.1 http://blogs.sanmathi.org/nalanda/2008/10/08/exor-opportunistic-multi-hop-routing-for-wireless-networks/#comment-43 Ashwin Thu, 09 Oct 2008 01:34:06 +0000 http://blogs.sanmathi.org/nalanda/?p=169#comment-43 I'll concede that overall spectrum utilization is good; but my question is related to throughput from multiple sources. The restriction to one source sending at a time, and strict ordering of sources, seems to imply that sources will be constrained by other sources, leading to poor network utilization, and probably the TCP backoff issues that we've already discussed. I’ll concede that overall spectrum utilization is good; but my question is related to throughput from multiple sources. The restriction to one source sending at a time, and strict ordering of sources, seems to imply that sources will be constrained by other sources, leading to poor network utilization, and probably the TCP backoff issues that we’ve already discussed.

]]> http://blogs.sanmathi.org/nalanda/2008/10/08/exor-opportunistic-multi-hop-routing-for-wireless-networks/#comment-42 Matthias Goerner Thu, 09 Oct 2008 01:28:07 +0000 http://blogs.sanmathi.org/nalanda/?p=169#comment-42 "The requirement for ordering of transmissions amongst all forwarders surprised me;" I guess that for really large networks where there is absolutely no way of the node on the outer edge overhearing a node in the middle, this will probably be relaxed for efficiency. But let's assume this is not the case, let's assume a graph like A-B-C-D, B can send to A and C to D without collision (because signal difference is at least 10dB). This is what you were expecting that several stations send at the same time. But notice that B can also send to D directly, but only if C is not sending. That means that B can send a packet to D directly and we save a hop, but it requires that C is silent during that time. In short, if only one node is sending at a time, the signal is propagating further without being dominated by other signals and needs less hops. And since less hops means less number of total transmissions, the overall usage of the spectrum is pretty good. “The requirement for ordering of transmissions amongst all forwarders surprised me;” I guess that for really large networks where there is absolutely no way of the node on the outer edge overhearing a node in the middle, this will probably be relaxed for efficiency.
But let’s assume this is not the case, let’s assume a graph like A-B-C-D, B can send to A and C to D without collision (because signal difference is at least 10dB). This is what you were expecting that several stations send at the same time.
But notice that B can also send to D directly, but only if C is not sending. That means that B can send a packet to D directly and we save a hop, but it requires that C is silent during that time.
In short, if only one node is sending at a time, the signal is propagating further without being dominated by other signals and needs less hops. And since less hops means less number of total transmissions, the overall usage of the spectrum is pretty good.

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