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RE: TCP state machine

  • From: "Hull, Kenneth A." <KHULL@alleghenyenergy.com>
  • Date: Fri, 15 Feb 2002 12:30:44 -0500
  • Cc: "'ahussain@eng.utoledo.edu'" <ahussain@eng.utoledo.edu>
  • Resent-Date: Fri, 15 Feb 2002 13:20:20 -0500
  • To: "'Mohammed'" <ipswitching@yahoo.com>, "'mpls-ops@mplsrc.com'" <mpls-ops@mplsrc.com>

I would suggest you build a timer to take either end of the session back to
the previous state if the an appropriate response is not received in the
timer window, and be sure your software ignores any extra messages
corresponding to move form the previous state it may receive for the same
session (same source TCP port) once it moves to the next state.

-----Original Message-----
From: Mohammed [mailto:ipswitching@yahoo.com]
Sent: Wednesday, February 13, 2002 11:08 AM
To: mpls-ops@mplsrc.com
Cc: ahussain@eng.utoledo.edu
Subject: TCP state machine


Hi all,

 I was writing the code for TCP state machine so that
i could use it for running LDP over TCP. This would
just be a component of the simulator that i am working
on.

 I was looking at the state transition diagram given
in TCP/IP illustrated Vol 1 by Richard Stevens.

 Please consider the following scenario --

 A TCP software on a peer working on passive open mode
is in "SYN-RCVD" state. It is waiting for an 'ACK'
from its peer on the other end of the connection.
There are two things that might happen here ...

 (1) SYN + ACK sent before transition to this state
was lost, so the other side never received it and
hence never ACK.

 (2) The other side have received it and had ACk but
the ACk was lost.

 Anyways 'SYN-RCVD' i waiting for an ACK. But during
its wait period or even before its time oust and sends
RST ... if it receives an appl:close interrupt then it
is supposed to send a FIN to its peer.

 Now if the peer on the other side is in 

 -- "ESTB" state then this would be okay.
 
 But if it is "SYN SENT" state .. then how am i
supposed to handle this FIN.

 Any pointers from TCP developers or any other
interested professionals are welcome.

 Thanks for your time and help!!!
 Abrar.
 

=====
Abrar Hussain.
Graduate Student/Network Designer.
The University of Toledo.
Toledo,OH.

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