I would like to have a stab at this, please.
Say you have a window of ten frames between these machines; meaning
machine ONE can send out ten frames before expecting an ACK from machine
TWO.
If an ack is received by machine ONE somewhere in between the first and
last frames send (1-10); this means machine TWO is ack'ing the last good
frame received from machine ONE.
And machine ONE should resend starting with that frame number going
forward so that machine TWO gets the entire [whatever] in good
condition; no lost frames, no CRC that didn't check out; etc.
-----Original Message-----
From: ethereal-users-bounces@xxxxxxxxxxxx
[mailto:ethereal-users-bounces@xxxxxxxxxxxx] On Behalf Of
JamesHorwath@xxxxxxxx
Sent: Thursday, August 11, 2005 10:04 AM
To: ethereal-users@xxxxxxxxxxxx
Subject: [Ethereal-users] sequence/acknowledgement number question
I have a question regarding how tcp sequence numbers are calculated
and/or acknowledged. I reviewed the RFC, Steven's, and other resources
and what I read does not jive with what I see displayed or what happens
in the read world. What I read is the acknowledgement number is one
greater than the
sequence number. This seems to only hold true if there is zero bytes
of
data sent. In example one I see the acknowledgement number 3322332584
for the sequence number 3322332583:3322332583(0)
Example 1:
15:45:13.141102 IP (tos 0x0, ttl 60, id 22513, offset 0, flags [none],
length:60) 10.10.10.241.37679 > 10.10.10.145.22: S
3322332583:3322332583(0) win 65535 <mss 1460,nop,wscale
4,nop,nop,timestamp[|tcp]>
15:45:13.141468 IP (tos 0x0, ttl 60, id 63343, offset 0, flags [none],
length:60) 10.10.10.145.22 > 10.10.10.241.37679: S
3524895916:3524895916(0) ack 3322332584 win 17376 <mss 1460,nop,wscale
0,nop,nop,timestamp[|tcp]>
Now example two seems to blow the acknowledgement numbers as I read
about them. The sequence numbers are 3322333792:3322334032, I would
expect the acknowledgement number to be 3322334033 not 3322334032. Why
is the ack
3322334032 and not 3322334033. I have been pulling what's left of my
hair out. I have asked a Track 3 alumni and the two network dudes and
they were equally perplexed as I was when I showed them this data.
Example 2:
15:45:14.356295 IP (tos 0x0, ttl 60, id 22570, offset 0, flags [none],
length:292) 10.10.10.241.37679 > 10.10.10.145.22: P
3322333792:3322334032(240) ack 354898565 win 32761 <nop,nop,timestamp
1125902767 1122933152>
15:45:14.359383 IP (tos 0x0, ttl 60, id 63509, offset 0, flags [none],
length:244) 10.10.10.145.22 > 10.10.10.241.37679: P
3524898565:3524898757(192) ack 3322334032 win 17376 <nop,nop,timestamp
1122933152 1125902767>
I would really appreciate if somebody could explain this too me. This
has been eating away at me and I am assuming it is something very
simple.
Regards,
Jim
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