[1245] in linux-net channel archive
Asymmetric TCP/PPP performance (very poor receiving TCP)
daemon@ATHENA.MIT.EDU (Robert L Krawitz)
Wed Oct 25 02:14:53 1995
Date: Tue, 24 Oct 1995 10:18:44 -0400
From: Robert L Krawitz <rlk@tiac.net>
To: linux-net@vger.rutgers.edu
Running linux 1.3.27 or 1.2.13, ppp 2.1.2 or 2.2.0 on a 28.8K modem
(Sportster V.34 or Infotel V.FC) on a Pentium 90 system, I get about
11 KB/sec sending a file of all null's (i. e. perfectly compressible)
from my system to a Sun4 on an ethernet. Receiving, I get about 5
KB/sec. I specify an async map of 0 and the log indicates that I'm
successfully negotiating that. If I set my serial port to a lower
speed (57.6 or 38.4), I get proportionately lower throughput both
sending and receiving. My PPP connection is through a Cisco 2509
router. Furthermore, CONFIG_SKB_LARGE doesn't affect the
performance. I'm using 1500 as my MTU.
tcpdump shows that when receiving data I send out a lot of ack's whose
sole purpose seems to be to increase the window after ftp pulls each
chunk of data off. Given that the window's never falling very low,
these ack's seem excessive and probably degrade bandwidth. In these
traces, rlk-ppp-1 is my machine and bloch is the remote machine.
I stared at the TCP code for a while but didn't make any headway into
this. Is this problem known? Has anyone else seen it?
Receiving data (slow):
15:50:27.017304 rlk-ppp-1.1067 > bloch.20: . ack 35689 win 13527 [tos 0x8]
15:50:27.267308 rlk-ppp-1.1067 > bloch.20: . ack 35689 win 14335 [tos 0x8]
15:50:27.267308 bloch.20 > rlk-ppp-1.1067: . 35689:37149(1460) ack 1 win 24820 (DF)
15:50:27.267308 rlk-ppp-1.1067 > bloch.20: . ack 37149 win 13527 [tos 0x8]
15:50:27.527312 bloch.20 > rlk-ppp-1.1067: . 37149:38609(1460) ack 1 win 24820 (DF)
15:50:27.527312 rlk-ppp-1.1067 > bloch.20: . ack 38609 win 13527 [tos 0x8]
15:50:27.777316 rlk-ppp-1.1067 > bloch.20: . ack 38609 win 14335 [tos 0x8]
15:50:27.787316 bloch.20 > rlk-ppp-1.1067: P 38609:40069(1460) ack 1 win 24820 (DF)
15:50:27.787316 rlk-ppp-1.1067 > bloch.20: . ack 40069 win 13527 [tos 0x8]
15:50:27.937319 bloch.20 > rlk-ppp-1.1067: P 40069:40961(892) ack 1 win 24820 (DF)
15:50:27.937319 rlk-ppp-1.1067 > bloch.20: . ack 40961 win 13807 [tos 0x8]
15:50:28.187323 rlk-ppp-1.1067 > bloch.20: . ack 40961 win 14335 [tos 0x8]
15:50:28.197323 bloch.20 > rlk-ppp-1.1067: . 40961:42421(1460) ack 1 win 24820 (DF)
Sending data (fast):
15:50:59.737852 rlk-ppp-1.1071 > bloch.20: P 37525:38985(1460) ack 1 win 14335 [tos 0x8]
15:50:59.737852 rlk-ppp-1.1071 > bloch.20: P 38985:40445(1460) ack 1 win 14335 [tos 0x8]
15:50:59.847854 bloch.20 > rlk-ppp-1.1071: . ack 33145 win 24820 (DF)
15:50:59.847854 rlk-ppp-1.1071 > bloch.20: P 38985:40445(1460) ack 1 win 14335 [tos 0x8]
15:50:59.987856 bloch.20 > rlk-ppp-1.1071: . ack 34605 win 24820 (DF)
15:50:59.987856 rlk-ppp-1.1071 > bloch.20: P 38985:40445(1460) ack 1 win 14335 [tos 0x8]
15:51:00.117858 bloch.20 > rlk-ppp-1.1071: . ack 36065 win 24820 (DF)
15:51:00.117858 rlk-ppp-1.1071 > bloch.20: P 43365:44825(1460) ack 1 win 14335 [tos 0x8]
15:51:00.247860 bloch.20 > rlk-ppp-1.1071: . ack 37525 win 24820 (DF)
15:51:00.247860 rlk-ppp-1.1071 > bloch.20: P 43365:44825(1460) ack 1 win 14335 [tos 0x8]
15:51:00.377863 bloch.20 > rlk-ppp-1.1071: . ack 38985 win 24820 (DF)
15:51:00.377863 rlk-ppp-1.1071 > bloch.20: P 43365:44825(1460) ack 1 win 14335 [tos 0x8]
15:51:00.497865 bloch.20 > rlk-ppp-1.1071: . ack 40445 win 24820 (DF)
15:51:00.497865 rlk-ppp-1.1071 > bloch.20: P 46285:47745(1460) ack 1 win 14335 [tos 0x8]
15:51:00.627867 bloch.20 > rlk-ppp-1.1071: . ack 41905 win 24820 (DF)
--
Robert Krawitz <rlk@tiac.net> http://www.tiac.net/users/rlk/
Member of the League for Programming Freedom -- mail lpf@uunet.uu.net
Tall Clubs International -- tci-request@aptinc.com or 1-800-521-2512
