Re: Experiencing very slow browsing at times (atheros wireless)

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>]

:Just a few moments ago another slowness was happening so i ran the 2 
:tcpdump commands. After about 1-2 minutes it came back to normal speed 
:so i tcpdump.
:
:You/whoever wants can get the dumps here:
:
:http://www.punchyouremployer.com/files/tcpdump.tgz
:
:Please have a look and tell me if you can see something wrong.
:
:Petr

    It looks like you have a ton of packet loss somewhere.  What
    machine was the tcpdump run on?  It looks like you ran it on
    the web server.  I think what you want to do is run it on
    the client running the browser, not on the server.

    I am going to post an excerpt (open a wide xterm to view) from:
    tcpdump -n -s 4096 -r dump80211 | fgrep .80 | fgrep 2568 | less

    The web server, 140.211.166.170, is trying to transmit a
    full-sized TCP packet over and over again because it isn't
    getting an ack from the client.  See all the 7001:8401 packets?

    It's sending the same payload over and over again and it is
    backing off.  Either the large tcp packet is not making it to
    the client, or the client's ACK is not making it back to the
    server.

    It does NOT look like an MTU problem, because the client had
    no problem ack numerous full-sized TCP packets beforehand.

    It does look like a radio transmit/receive issue, but I don't
    think it is really possible to tell from the web server side.
    What we really need are the signal levels on the client side.

    One thing you couldtry would be to force the transmit rate
    way way down, and maybe try using a long preamble instead
    of a short preamble (if it is possible to set the preamble).
    A short preamble might not be enough to train the receiver
    DSP for the longer packets.

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>

09:58:02.547654 IP 192.168.1.50.2568 > 140.211.166.170.80: . ack 4201 win 57728 <nop,nop,timestamp 4940337 3127766652>
09:58:02.774822 IP 140.211.166.170.80 > 192.168.1.50.2568: . 4201:5601(1400) ack 691 win 15 <nop,nop,timestamp 3127766731 4940337>
09:58:02.776813 IP 140.211.166.170.80 > 192.168.1.50.2568: . 5601:7001(1400) ack 691 win 15 <nop,nop,timestamp 3127766731 4940337>
09:58:02.776859 IP 192.168.1.50.2568 > 140.211.166.170.80: . ack 4201 win 57728 <nop,nop,timestamp 4940359 3127766652,nop,nop,sack 1 {5601:7001}>
09:58:03.003406 IP 140.211.166.170.80 > 192.168.1.50.2568: . 7001:8401(1400) ack 691 win 15 <nop,nop,timestamp 3127766789 4940359>
09:58:03.455055 IP 140.211.166.170.80 > 192.168.1.50.2568: . 4201:5601(1400) ack 691 win 15 <nop,nop,timestamp 3127766902 4940359>
09:58:04.822746 IP 140.211.166.170.80 > 192.168.1.50.2568: . 4201:5601(1400) ack 691 win 15 <nop,nop,timestamp 3127767244 4940359>
09:58:04.822798 IP 192.168.1.50.2568 > 140.211.166.170.80: . ack 7001 win 54928 <nop,nop,timestamp 4940564 3127767244>
09:58:05.048597 IP 140.211.166.170.80 > 192.168.1.50.2568: . 7001:8401(1400) ack 691 win 15 <nop,nop,timestamp 3127767300 4940564>
09:58:05.052042 IP 140.211.166.170.80 > 192.168.1.50.2568: . 8401:9801(1400) ack 691 win 15 <nop,nop,timestamp 3127767300 4940564>
09:58:05.702975 IP 140.211.166.170.80 > 192.168.1.50.2568: . 7001:8401(1400) ack 691 win 15 <nop,nop,timestamp 3127767464 4940564>
09:58:07.015773 IP 140.211.166.170.80 > 192.168.1.50.2568: . 7001:8401(1400) ack 691 win 15 <nop,nop,timestamp 3127767792 4940564>
09:58:09.638984 IP 140.211.166.170.80 > 192.168.1.50.2568: . 7001:8401(1400) ack 691 win 15 <nop,nop,timestamp 3127768448 4940564>
09:58:14.887620 IP 140.211.166.170.80 > 192.168.1.50.2568: . 7001:8401(1400) ack 691 win 15 <nop,nop,timestamp 3127769760 4940564>
09:58:24.728513 IP 192.168.1.50.2568 > 140.211.166.170.80: F 691:691(0) ack 7001 win 57728 <nop,nop,timestamp 4942555 3127767244>
09:58:24.951122 IP 140.211.166.170.80 > 192.168.1.50.2568: . ack 692 win 15 <nop,nop,timestamp 3127772278 4942555>
09:58:25.380812 IP 140.211.166.170.80 > 192.168.1.50.2568: . 7001:8401(1400) ack 692 win 15 <nop,nop,timestamp 3127772384 4942555>
09:58:46.370675 IP 140.211.166.170.80 > 192.168.1.50.2568: . 7001:8401(1400) ack 692 win 15 <nop,nop,timestamp 3127777632 4942555>
09:59:28.353154 IP 140.211.166.170.80 > 192.168.1.50.2568: . 7001:8401(1400) ack 692 win 15 <nop,nop,timestamp 3127788128 4942555>
09:59:28.353206 IP 192.168.1.50.2568 > 140.211.166.170.80: R 257286875:257286875(0) win 0