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@xxxxxxxx
http://www.ccrle.nec.de/heidelberg/index.html
Tel.: +49.(0)6221.13 70 819 Fax: +49.(0)6221.905
11 55
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
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