[OLSR-users] LQ Routing and 802.11b Link Speed

[Holger Mauermann]

Bruno Randolf wrote:
> to get the expected transmission times we would have to send unicast
> packets to each neighbor (the current HELLO packets are broadcast
> with the lowest basic rate) which can result in a lot of additionally
> used bandwidth.

yes, but the link speed usually doesn't change very often (with fixed 
stations), e.g. the link to one of my neighbors changes 5 to 10 times 
per hour between 18, 24 and 36 Mbps and a bad 1 Mbps link always stays 
at 1 Mbps. So I think it's adequate if the packet-pair to measure the 
bandwidth is sent at intervals of several minutes.

> another option may be to read the current rate (physical link speed)
> from the wlan driver and multiply the ETX with that value.

This is very OS and driver dependent. I've recently seen an USB adapter
with ndiswrapper that always reports 54 Mbps...

> could you send a link to the ETT paper?

Yes, of course [1]. However, it's from Micro$oft ;-)

I found another interesting paper about Medium Time Metric MTM [2]. Its 
idea ("minimize the usage of a shared medium to maximize its capacity") 
is similar to ETT and the authors measured up to 17 times more 
throughput compared to min hop and ETX routing...

[1]-http://research.microsoft.com/mesh/papers/multiradio.pdf
[2]-http://www.cnds.jhu.edu/research/networks/archipelago/publications/AHR-MediumTimeMetric-TechnicalReport.pdf

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