Retransmission timer in TCP

<Ext-Rafael.M.Sanchez@nokia.com> Wed, 04 December 2002 11:17 UTC

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Subject: Retransmission timer in TCP
Date: Wed, 04 Dec 2002 12:17:46 +0100
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Thread-Topic: Retransmission timer in TCP
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From: Ext-Rafael.M.Sanchez@nokia.com
To: tcp-impl@grc.nasa.gov
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  Hi all,

  RTO computation as in recommended in RFC2988 uses one retransmission timer per transmission window. Does this provide a more robust solution than having one retransmission timer per segment ? 

  I mean:

 1) In the first case any ACK that acknowledges new data resets the timer, so increasing the transmission window ( and RTT) provides a more conservative retransmission timer. Because, RTO *RTT(one packet) + TxWindowDelay(because of buffering), and time for next ACK is roughly RTT(one packet).

 2) In the second case, the retransmission timer of one packet would be only reset when that packet is acknowledged, so time for ACK * RTT(one packet) + TxWindowDelay, and the retransmission timer would be more sensible to delay spikes ( eg. likely in wireless networks). 

  I haven't found much information about how second option is implemented, maybe it is implemented in a different way. Do you know some reference that discuss this difference?. Or maybe this is not really an issue, I'm not sure about if the option 2) is really widely used, or it is really that most common systems (Windows, Solaris, Linux ... etc) just implement RFC2988. 

  Thanks in advance,
  Best regards,
  Rafa

Retransmission timer in TCP Ext-Rafael.M.Sanchez
Re: Retransmission timer in TCP Mark Allman