[e2e] What's wrong with this picture?
Jon Crowcroft
Jon.Crowcroft at cl.cam.ac.uk
Mon Sep 7 01:39:11 PDT 2009
so you've got a slow uplink and fast downlink - it doesn't look
like xDSL - is it a really overloaded 3G or 2.5G link? (if there's
congestion in the "air" interface, you might get this sort of
thing...)
In missive <4AA45B20.6030705 at reed.com>, "David P. Reed" typed:
>>This is a multi-part message in MIME format.
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>>For those who have some idea of how TCP does congestion control, I ask
>>"what's wrong with this picture?" And perhaps those who know someone
>>responsible at the Internet Access Provider involved, perhaps we could
>>organize some consulting help...
>>
>>(Hint: the problem relates to a question, "why are there no lost IP
>>datagrams?", and a second hint is that the ping time this morning was
>>about 193 milliseconds.)
>>
>>Van Jacobsen, Scott Shenker, and Sally Floyd are not allowed to answer
>>the question. (they used to get funding from the IAP involved, but
>>apparently that company does not listen to them).
>>
>>$ ping lcs.mit.edu
>>PING lcs.mit.edu (128.30.2.121) 56(84) bytes of data.
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=1 ttl=44
>>time=6330 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=2 ttl=44
>>time=6005 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=3 ttl=44
>>time=8509 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=4 ttl=44
>>time=9310 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=5 ttl=44
>>time=8586 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=6 ttl=44
>>time=7765 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=7 ttl=44
>>time=7168 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=8 ttl=44
>>time=10261 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=9 ttl=44
>>time=10624 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=10 ttl=44
>>time=9625 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=11 ttl=44
>>time=9725 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=12 ttl=44
>>time=8725 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=13 ttl=44
>>time=9306 ms
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=14 ttl=44
>>time=8306 ms
>>^C
>>--- lcs.mit.edu ping statistics ---
>>24 packets transmitted, 14 received, 41% packet loss, time 33174ms
>>rtt min/avg/max/mdev = 6005.237/8589.365/10624.776/1334.140 ms, pipe 11
>>$ traceroute lcs.mit.edu
>>traceroute to lcs.mit.edu (128.30.2.121), 30 hops max, 60 byte packets
>> 1 * * *
>> 2 172.26.248.2 (172.26.248.2) 693.585 ms 693.415 ms 712.282 ms
>> 3 * * *
>> 4 172.16.192.18 (172.16.192.18) 712.700 ms 1356.680 ms 1359.469 ms
>> 5 12.88.7.205 (12.88.7.205) 1361.306 ms 673.642 ms 673.541 ms
>> 6 cr84.cgcil.ip.att.net (12.122.152.134) 673.442 ms 673.371 ms
>>673.742 ms
>> 7 cr2.cgcil.ip.att.net (12.123.7.250) 655.126 ms 654.186 ms 554.690 ms
>> 8 * * ggr2.cgcil.ip.att.net (12.122.132.133) 912.385 ms
>> 9 192.205.33.210 (192.205.33.210) 909.925 ms 911.335 ms 911.204 ms
>>10 ae-31-53.ebr1.Chicago1.Level3.net (4.68.101.94) 569.740 ms 569.605
>>ms 907.409 ms
>>11 ae-1-5.bar1.Boston1.Level3.net (4.69.140.93) 369.680 ms 344.495
>>ms 345.252 ms
>>12 ae-7-7.car1.Boston1.Level3.net (4.69.132.241) 355.645 ms 641.866
>>ms 641.367 ms
>>13 MASSACHUSET.car1.Boston1.Level3.net (4.53.48.98) 636.598 ms
>>636.797 ms 635.755 ms
>>14 B24-RTR-2-BACKBONE-2.MIT.EDU (18.168.1.23) 635.766 ms 634.794 ms
>>866.430 ms
>>15 MITNET.TRANTOR.CSAIL.MIT.EDU (18.4.7.65) 758.305 ms 822.244 ms
>>821.202 ms
>>16 trantor.kalgan.csail.mit.edu (128.30.0.246) 833.699 ms 1055.548
>>ms 1116.813 ms
>>17 zermatt.csail.mit.edu (128.30.2.121) 1114.838 ms 539.951 ms
>>620.681 ms
>>[david at whimsy ~]$ ping 172.26.248.2
>>PING 172.26.248.2 (172.26.248.2) 56(84) bytes of data.
>>64 bytes from 172.26.248.2: icmp_seq=1 ttl=254 time=1859 ms
>>64 bytes from 172.26.248.2: icmp_seq=2 ttl=254 time=1363 ms
>>64 bytes from 172.26.248.2: icmp_seq=3 ttl=254 time=1322 ms
>>64 bytes from 172.26.248.2: icmp_seq=4 ttl=254 time=1657 ms
>>64 bytes from 172.26.248.2: icmp_seq=5 ttl=254 time=1725 ms
>>64 bytes from 172.26.248.2: icmp_seq=6 ttl=254 time=1740 ms
>>64 bytes from 172.26.248.2: icmp_seq=7 ttl=254 time=1838 ms
>>64 bytes from 172.26.248.2: icmp_seq=8 ttl=254 time=1738 ms
>>64 bytes from 172.26.248.2: icmp_seq=9 ttl=254 time=1517 ms
>>64 bytes from 172.26.248.2: icmp_seq=10 ttl=254 time=978 ms
>>64 bytes from 172.26.248.2: icmp_seq=11 ttl=254 time=715 ms
>>64 bytes from 172.26.248.2: icmp_seq=12 ttl=254 time=678 ms
>>64 bytes from 172.26.248.2: icmp_seq=13 ttl=254 time=638 ms
>>64 bytes from 172.26.248.2: icmp_seq=14 ttl=254 time=761 ms
>>^C
>>--- 172.26.248.2 ping statistics ---
>>15 packets transmitted, 14 received, 6% packet loss, time 14322ms
>>rtt min/avg/max/mdev = 638.651/1324.002/1859.725/455.200 ms, pipe 2
>>$
>>
>>
>>--------------020400030709090500010400
>>Content-Type: text/html; charset=ISO-8859-1
>>Content-Transfer-Encoding: 7bit
>>
>><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
>><html>
>><head>
>>
>><meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
>></head>
>><body text="#000000" bgcolor="#ffffff">
>><font face="Helvetica, Arial, sans-serif">For those who have some idea
>>of how TCP does congestion control, I ask "what's wrong with this
>>picture?" And perhaps those who know someone responsible at the
>>Internet Access Provider involved, perhaps we could organize some
>>consulting help...<br>
>><br>
>>(Hint: the problem relates to a question, "why are there no lost IP
>>datagrams?", and a second hint is that the ping time this morning was
>>about 193 milliseconds.)<br>
>><br>
>>Van Jacobsen, Scott Shenker, and Sally Floyd are not allowed to answer
>>the question. (they used to get funding from the IAP involved, but
>>apparently that company does not listen to them).<br>
>><br>
>>$ ping lcs.mit.edu<br>
>>PING lcs.mit.edu (128.30.2.121) 56(84) bytes of data.<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=1 ttl=44
>>time=6330 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=2 ttl=44
>>time=6005 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=3 ttl=44
>>time=8509 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=4 ttl=44
>>time=9310 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=5 ttl=44
>>time=8586 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=6 ttl=44
>>time=7765 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=7 ttl=44
>>time=7168 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=8 ttl=44
>>time=10261 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=9 ttl=44
>>time=10624 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=10 ttl=44
>>time=9625 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=11 ttl=44
>>time=9725 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=12 ttl=44
>>time=8725 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=13 ttl=44
>>time=9306 ms<br>
>>64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=14 ttl=44
>>time=8306 ms<br>
>>^C<br>
>>--- lcs.mit.edu ping statistics ---<br>
>>24 packets transmitted, 14 received, 41% packet loss, time 33174ms<br>
>>rtt min/avg/max/mdev = 6005.237/8589.365/10624.776/1334.140 ms, pipe 11<br>
>>$ traceroute lcs.mit.edu<br>
>>traceroute to lcs.mit.edu (128.30.2.121), 30 hops max, 60 byte packets<br>
>> 1 * * *<br>
>> 2 172.26.248.2 (172.26.248.2) 693.585 ms 693.415 ms 712.282 ms<br>
>> 3 * * *<br>
>> 4 172.16.192.18 (172.16.192.18) 712.700 ms 1356.680 ms 1359.469 ms<br>
>> 5 12.88.7.205 (12.88.7.205) 1361.306 ms 673.642 ms 673.541 ms<br>
>> 6 cr84.cgcil.ip.att.net (12.122.152.134) 673.442 ms 673.371 ms
>>673.742 ms<br>
>> 7 cr2.cgcil.ip.att.net (12.123.7.250) 655.126 ms 654.186 ms
>>554.690 ms<br>
>> 8 * * ggr2.cgcil.ip.att.net (12.122.132.133) 912.385 ms<br>
>> 9 192.205.33.210 (192.205.33.210) 909.925 ms 911.335 ms 911.204 ms<br>
>>10 ae-31-53.ebr1.Chicago1.Level3.net (4.68.101.94) 569.740 ms
>>569.605 ms 907.409 ms<br>
>>11 ae-1-5.bar1.Boston1.Level3.net (4.69.140.93) 369.680 ms 344.495
>>ms 345.252 ms<br>
>>12 ae-7-7.car1.Boston1.Level3.net (4.69.132.241) 355.645 ms 641.866
>>ms 641.367 ms<br>
>>13 MASSACHUSET.car1.Boston1.Level3.net (4.53.48.98) 636.598 ms
>>636.797 ms 635.755 ms<br>
>>14 B24-RTR-2-BACKBONE-2.MIT.EDU (18.168.1.23) 635.766 ms 634.794 ms
>>866.430 ms<br>
>>15 MITNET.TRANTOR.CSAIL.MIT.EDU (18.4.7.65) 758.305 ms 822.244 ms
>>821.202 ms<br>
>>16 trantor.kalgan.csail.mit.edu (128.30.0.246) 833.699 ms 1055.548
>>ms 1116.813 ms<br>
>>17 zermatt.csail.mit.edu (128.30.2.121) 1114.838 ms 539.951 ms
>>620.681 ms<br>
>>[david at whimsy ~]$ ping 172.26.248.2<br>
>>PING 172.26.248.2 (172.26.248.2) 56(84) bytes of data.<br>
>>64 bytes from 172.26.248.2: icmp_seq=1 ttl=254 time=1859 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=2 ttl=254 time=1363 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=3 ttl=254 time=1322 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=4 ttl=254 time=1657 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=5 ttl=254 time=1725 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=6 ttl=254 time=1740 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=7 ttl=254 time=1838 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=8 ttl=254 time=1738 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=9 ttl=254 time=1517 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=10 ttl=254 time=978 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=11 ttl=254 time=715 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=12 ttl=254 time=678 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=13 ttl=254 time=638 ms<br>
>>64 bytes from 172.26.248.2: icmp_seq=14 ttl=254 time=761 ms<br>
>>^C<br>
>>--- 172.26.248.2 ping statistics ---<br>
>>15 packets transmitted, 14 received, 6% packet loss, time 14322ms<br>
>>rtt min/avg/max/mdev = 638.651/1324.002/1859.725/455.200 ms, pipe 2<br>
>>$<br>
>><br>
>></font>
>></body>
>></html>
>>
>>--------------020400030709090500010400--
cheers
jon
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