Received: by oss.sgi.com id ; Fri, 5 Jan 2001 05:34:50 -0800 Received: from yamato.ccrle.nec.de ([195.37.70.1]:55559 "EHLO yamato.ccrle.nec.de") by oss.sgi.com with ESMTP id ; Fri, 5 Jan 2001 05:34:35 -0800 Received: from wallace.heidelberg.ccrle.nec.de (root@Wallace.heidelberg.ccrle.nec.de [192.168.102.1]) by yamato.ccrle.nec.de (8.10.1/8.10.1) with ESMTP id f05DZ1B01967 for ; Fri, 5 Jan 2001 14:35:01 +0100 (CET) Received: from ccrle.nec.de (judiciary.heidelberg.ccrle.nec.de [192.168.102.83]) by wallace.heidelberg.ccrle.nec.de (8.9.3/8.9.3/SuSE Linux 8.9.3-0.1) with ESMTP id OAA01067 for ; Fri, 5 Jan 2001 14:34:32 +0100 Message-ID: <3A55CF54.8C890679@ccrle.nec.de> Date: Fri, 05 Jan 2001 14:42:44 +0100 From: Karl Jonas Organization: NEC CCRLE X-Mailer: Mozilla 4.76 [en] (WinNT; U) X-Accept-Language: en MIME-Version: 1.0 To: netdev@oss.sgi.com Subject: looking for info about struct tcp_opt Content-Type: multipart/mixed; boundary="------------10BE7A57E9CA273E1D2F3244" Sender: owner-netdev@oss.sgi.com Precedence: bulk Return-Path: X-Orcpt: rfc822;netdev-outgoing Content-Length: 8380 Lines: 123 This is a multi-part message in MIME format. --------------10BE7A57E9CA273E1D2F3244 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Dear all, I am looking for some information about the members of the 'struct tcp_opt' in the linux kernel. Please help me with answers or references to the right place/person/doc. Thanks in advance, Karl Jonas WHY DOES SND_WND DECREASE, RATHER THAN INCREASE ? According to rfc761, snd.wnd is the send window, which includes both the number of unacknowledged bytes and the number of bytes that may be transmitted before any ack arrives. >From this, i expect snd_wnd to increase exponentially (slow start) and than to alter around some high value, maybe decreasing in the case of transmission errors. What i see is that the snd_wnd starts with a high value and decreases continuously, sometimes shows a sharp increase, sometimes stays around zero for a while. (my observations come from a transmission on a local machine, with tcpdump showing that it is error-free). Interestingly, the value of 'packets_out' alters between 0 and 1, which is what i would expect. A trace is provided in the attached file which was made by a tcp sender transmitting 1kB packets as fast as possible on to a receiver on the local machine. WHAT IS THE UNIT OF SRTT? According to its declaration in sock.h, it is the 'smoothed rtt << 3' . Does this mean, that the value '8', which i observed, corresponds to a round trip time of about 1 ms ? WHAT IS THE UNIT OF SND_CWND? In my trace, snd_cwnd initialises with 3 and increases by 1 for each packet sent (acked?), and slower after, corresponding perfectly to slow start / congestion avoidance. But what is the real size of the congestion window (maybe snd_cwnd * mss ?) ? WHAT IS THE RTO UNIT? I see a rto of 20. This seems to be quite short if it was 20 ms. Does linux count in 10's of ms here? -- Karl Jonas, NEC Research Labs Adenauerplatz 6, 69115 Heidelberg EMail: karl.jonas@ieee.org http://www.ccrle.nec.de/heidelberg/index.html Tel.: +49.(0)6221.13 70 819 Fax: +49.(0)6221.905 11 55 --------------10BE7A57E9CA273E1D2F3244 Content-Type: text/plain; charset=us-ascii; name="output.txt" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="output.txt" pnum rcv_nxt snd_nxt snd_una rcv_tstamp lrcvtime srtt snd_wnd max_window snd_cwnd rto packets_out rcv_wnd 1 923103371 930938866 930938866 559095 0 8 30072 31072 3 20 0 31072 2 923103371 930939866 930939866 559095 0 8 29072 31072 4 20 0 31072 3 923103371 930940866 930940866 559095 0 8 28072 31072 5 20 0 31072 4 923103371 930941866 930941866 559096 0 8 27072 31072 6 20 0 31072 5 923103371 930942866 930942866 559096 0 8 26072 31072 7 20 0 31072 6 923103371 930943866 930943866 559096 0 8 25072 31072 8 20 0 31072 7 923103371 930944866 930944866 559096 0 8 24072 31072 9 20 0 31072 8 923103371 930945866 930945866 559096 0 8 23072 31072 10 20 0 31072 9 923103371 930946866 930946866 559096 0 8 22072 31072 11 20 0 31072 10 923103371 930947866 930947866 559096 0 8 21072 31072 12 20 0 31072 11 923103371 930948866 930948866 559096 0 8 20072 31072 13 20 0 31072 12 923103371 930949866 930949866 559097 0 8 19072 31072 14 20 0 31072 13 923103371 930950866 930950866 559097 0 8 18072 31072 15 20 0 31072 14 923103371 930951866 930951866 559097 0 8 17072 31072 16 20 0 31072 15 923103371 930952866 930952866 559097 0 8 16072 31072 17 20 0 31072 16 923103371 930953866 930953866 559097 0 8 15072 31072 18 20 0 31072 17 923103371 930954866 930954866 559097 0 8 14072 31072 19 20 0 31072 18 923103371 930955866 930955866 559098 0 8 13072 31072 20 20 0 31072 19 923103371 930956866 930956866 559098 0 8 12072 31072 21 20 0 31072 20 923103371 930957866 930957866 559098 0 8 11072 31072 22 20 0 31072 21 923103371 930958866 930958866 559098 0 8 10072 31072 23 20 0 31072 22 923103371 930959866 930959866 559098 0 8 9072 31072 24 20 0 31072 23 923103371 930960866 930960866 559098 0 8 8072 31072 25 20 0 31072 24 923103371 930961866 930961866 559098 0 8 7072 31072 26 20 0 31072 25 923103371 930962866 930962866 559099 0 8 6072 31072 27 20 0 31072 26 923103371 930963866 930963866 559099 0 8 5072 31072 28 20 0 31072 27 923103371 930964866 930964866 559099 0 8 4072 31072 29 20 0 31072 28 923103371 930965866 930965866 559099 0 8 3072 31072 30 20 0 31072 29 923103371 930966866 930966866 559099 0 8 2072 31072 31 20 0 31072 30 923103371 930967866 930967866 559099 0 8 1072 31072 32 20 0 31072 31 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 32 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 33 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 34 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 35 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 36 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 37 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 38 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 39 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 40 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 41 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 42 923103371 930968866 930968866 559099 0 8 72 31072 33 20 0 31072 43 923103371 930972738 930968866 559100 0 8 3872 31072 33 20 1 31072 44 923103371 930972738 930968866 559100 0 8 3872 31072 33 20 1 31072 45 923103371 930972738 930968866 559100 0 8 3872 31072 33 20 1 31072 46 923103371 930972738 930968866 559100 0 8 3872 31072 33 20 1 31072 47 923103371 930976610 930972738 559100 0 8 3872 31072 34 20 1 31072 48 923103371 930976610 930976610 559101 0 8 0 31072 35 20 0 31072 49 923103371 930976610 930976610 559101 0 8 0 31072 35 20 0 31072 50 923103371 930976610 930976610 559101 0 8 0 31072 35 20 0 31072 --------------10BE7A57E9CA273E1D2F3244--