[e2e] How many transmission attempts should be done on wireless networks?

David P. Reed dpreed at reed.com
Fri Sep 18 18:13:22 PDT 2009

Let me clarify that in making my comment about 802.11 systems that won't 
stop retransmitting until 255 tries have been made, I was citing Larry 
Roberts.   I have not done such measurements.   If Larry is right and 
common chipsets retry up to 255 tries, I support his point.  Not 
everything Larry says is something I agree with, and I have not 
independently done a test of current chipsets myself.

If no one else has done so, I may do those tests myself....  after the 
observations of ATT's 8-10 second backlogs, I'm starting to believe 
there are likely to be lots of vendor supplied equipment that may fail 
to signal congestion backlogs properly.   Has anyone surveyed 
currently-on-the-market 802.11 implementations for overly heroic 
retransmission strategies?  Hari B. did a number of them, but I haven't 
seen a published dataset.

Note, if a shared channel like "listen-before-talk" wireless Ethernet is 
buffered among all competing flows, merely holding on to a few packets 
per interface can destroy end-to-end congestion control by creating a 
slow-to-drain backlog, if the number of interfaces sharing a common 
channel is large.

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