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From: bradg@zaphod.UUCP (Brad Gorzitza)
Newsgroups: comp.protocols.tcp-ip
Subject: Two TCP Queries
Message-ID: <4132@zaphod.UUCP>
Date: 6 Feb 91 20:08:31 GMT
Distribution: na
Organization: Develcon Electronics Limited,Saskatoon, SK, Canada
Lines: 66



        I have two tcp questions for this news group.  My  apo-
   logies  if  the  answers appear in the RFC's somewhere or if
   these questions have been  answered  here  before.   Anyway,
   here goes.

        First question: consider the following setup.

    ---------------     -------                  -------    ---------------
    | Application |     | TCP |==================| TCP |    | Application |
    |     A       |+++++|  A  |       Lan        |  B  |++++|     B       |
    _______________     _______    Connection    _______    _______________



        Application A stops accepting data from TCP A.   Appli-
   cation  B  continues sending data via TCP B until TCP A runs
   out of buffers and advertises window of 0.  After  a  while,
   Application B closes the connection.  What should TCP B do?

        According to RFC 793, SYN and FIN are included  in  the
   window (to give them retransmission protection).  Hence, TCP
   B supposedly cannot send a FIN until TCP A opens its  window
   again.   Is  this the case?  If I want TCP B to exit could I
   simply have it do so, perhaps after sending a RST?  Or am  I
   bound by the RFC's to let things run their course?

        Second question: consider  the  following.   TCP  A  is
   sending  data  to  TCP B.  *No* data is being sent the other
   way.

           TCP A                                        TCP B
           -----                                        -----

          send X bytes of data    --->               <received>
          seq # = Y  ack # = Z


              <lost>           <-----            seq # = Z  ack = X+Y


          send X bytes of data    --->               <Old data already
          seq # = Y  ack # = Z                       acked; silently
                                                       discarded>
                   .                .                      .
                   .                .                      .
                   .                .                      .
                   .                .                      .
           <connection reset at this
           end due to no response>


        My question is should TCP B  retransmit  its  ack  upon
   receiving a retransmission of data?


        Anyway, thanks in advance to any and all who reply.  As
   this  might be of interest to others, it might be an idea to
   reply to this newsgroup.

-- 
____________________________________________________________________________
Brad Gorzitza		bradg@zaphod.uucp
Develcon Electronics	"If this is the road we take to our dreams,
Saskatoon, Sask.	 do we walk in vain?"	T'Pau