[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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