rfc916.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Finn                                                           [Page 26]



RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


      A  --------------------------------------------------------

         This procedure details the behavior of the LISTEN state.  First
         check the packet for the RST flag.  If it is set then packet is
         discarded and ignored, return and continue the processing
         associated with this state.

         We assume now that the RST flag was not set.  Check the packet
         for the ACK flag.  If it is set we have an illegal condition
         since no connection has yet been opened.  Send a RST packet
         with the correct response SN value:

            <SN=received AN><CTL=RST>

         Return to the current state without any further processing.

         We assume now that neither the RST nor the ACK flags were set.
         Check the packet for a SYN flag.  If it is set then an attempt
         is being made to open a connection.  Create a TCB for this
         connection.  The sender has placed its MDL in the LENGTH field,
         also specified is the sender's initial SN value.  Retrieve and
         place them into the TCB.  Note that the presence of the SO flag
         is ignored since it has no meaning when either of the SYN, RST,
         or FIN flags are set.

         Send a SYN packet which acknowledges the SYN received.  Choose
         the initial SN value and the MDL for this end of the
         connection:

            <SN=0><AN=received SN+1 modulo 2><CTL=SYN, ACK><LENGTH=MDL>

         and go to the SYN-RECEIVED state without any further
         processing.

         Any packet not satisfying the above tests is discarded and
         ignored.  Return to the current state without any further
         processing.












Finn                                                           [Page 27]



RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


      B  --------------------------------------------------------

         This procedure represents the behavior of the SYN-SENT state
         and is entered when this end of the connection decides to
         execute an active OPEN.

         First, check the packet for the ACK flag.  If the ACK flag is
         set then check to see if the AN value was as expected.  If it
         was continue below.  Otherwise the AN value was unexpected.  If
         the RST flag was set then discard the packet and return to the
         current state without any further processing, else send a
         reset:

            <SN=received AN><CTL=RST>

         Discard the packet and return to the current state without any
         further processing.

         At this point either the ACK flag was set and the AN value was
         as expected or ACK was not set.  Second, check the RST flag.
         If the RST flag is set there are two cases:

            1. If the ACK flag is set then discard the packet, flush the
            retransmission queue, inform the user "Error: Connection
            refused", delete the TCB, and go to the CLOSED state without
            any further processing.

            2. If the ACK flag was not set then discard the packet and
            return to this state without any further processing.

         At this point we assume the packet contained an ACK which was
         Ok, or there was no ACK, and there was no RST.  Now check the
         packet for the SYN flag.  If the ACK flag was set then our SYN
         has been acknowledged.  Store MDL received in the TCB.  At this
         point we are technically in the ESTABLISHED state.  Send an
         acknowledgment packet and any initial data which is queued to
         send:

            <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK><DATA>

         Go to the ESTABLISHED state without any further processing.

         If the SYN flag was set but the ACK was not set then the other
         end of the connection has executed an active open also.
         Acknowledge the SYN, choose your MDL, and send:

            <SN=0><AN=received SN+1 modulo 2><CTL=SYN, ACK><LENGTH=MDL>


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RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


         Go to the SYN-RECEIVED state without any further processing.

         Any packet not satisfying the above tests is discarded and
         ignored.  Return to the current state without any further
         processing.

      C1 --------------------------------------------------------

         Examine the received SN field value.  If the SN value was
         expected then return and continue the processing associated
         with this state.

         We now assume the SN value was not what was expected.

         If either RST or FIN were set discard the packet and return to
         the current state without any further processing.

         If neither RST nor FIN flags were set it is assumed that this
         packet is a duplicate of one already received.  Send an ACK
         back:

            <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK>

         Discard the duplicate packet and return to the current state
         without any further processing.

      C2 --------------------------------------------------------

         Examine the received SN field value.  If the SN value was
         expected then return and continue the processing associated
         with this state.

         We now assume the SN value was not what was expected.

         If either RST or FIN were set discard the packet and return to
         the current state without any further processing.

         If SYN was set we assume that the other end crashed and has
         attempted to open a new connection.  We respond by sending a
         legal reset:

            <SN=received AN><AN=received SN+1 modulo 2><CTL=RST, ACK>

         This will cause the other end, currently in the SYN-SENT state,
         to close.  Flush the retransmission queue, inform the user
         "Error: Connection reset", discard the packet, delete the TCB,
         and go to the CLOSED state without any further processing.


Finn                                                           [Page 29]



RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


         If neither RST, FIN, nor SYN flags were set it is assumed that
         this packet is a duplicate of one already received.  Send an
         ACK back:

            <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK>

         Discard the duplicate packet and return to the current state
         without any further processing.

      D1 --------------------------------------------------------

         The packet is examined for a RST flag.  If RST is not set then
         return and continue the processing associated with this state.

         RST is now assumed to have been set.  If the connection was
         originally initiated from the LISTEN state (it was passively
         opened) then flush the retransmission queue, discard the
         packet, and go to the LISTEN state without any further
         processing.

         If instead the connection was initiated actively (came from the
         SYN-SENT state) then flush the retransmission queue, inform the
         user "Error: Connection refused", discard the packet, delete
         the TCB, and go to the CLOSED state without any further
         processing.

      D2 --------------------------------------------------------

         The packet is examined for a RST flag.  If RST is not set then
         return and continue the processing associated with this state.

         RST is now assumed to have been set.  Any data remaining to be
         sent is flushed.  The retransmission queue is flushed, the user
         is informed "Error: Connection reset.", discard the packet,
         delete the TCB, and go to the CLOSED state without any further
         processing.

      D3 --------------------------------------------------------

         The packet is examined for a RST flag.  If RST is not set then
         return and continue the processing associated with this state.

         RST is now assumed to have been set.  Discard the packet,
         delete the TCB, and go to the CLOSED state without any further
         processing.




Finn                                                           [Page 30]



RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


      E  --------------------------------------------------------

         Check the presence of the SYN flag.  If the SYN flag is not set
         then return and continue the processing associated with this
         state.

         We now assume that the SYN flag was set.  The presence of a SYN
         here is an error.  Flush the retransmission queue, send a legal
         RST packet.

            If the ACK flag was set then send:

               <SN=received AN><CTL=RST>

            If the ACK flag was not set then send:

               <SN=0><CTL=RST>

         The user should receive the message "Error: Connection reset.",
         then delete the TCB and go to the CLOSED state without any
         further processing.

      F1 --------------------------------------------------------

         Check the presence of the ACK flag.  If ACK is not set then
         discard the packet and return without any further processing.

         We now assume that the ACK flag was set.  If the AN field value
         was as expected then return and continue the processing
         associated with this state.

         We now assume that the ACK flag was set and that the AN field
         value was unexpected.  If the connection was originally
         initiated from the LISTEN state (it was passively opened) then
         flush the retransmission queue, discard the packet, and send a
         legal RST packet:

            <SN=received AN><CTL=RST>

         Then delete the TCB and go to the LISTEN state without any
         further processing.

         Otherwise the connection was initiated actively (came from the
         SYN-SENT state) then inform the user "Error: Connection
         refused", flush the retransmission queue, discard the packet,
         and send a legal RST packet:



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RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


            <SN=received AN><CTL=RST>

         Then delete the TCB and go to the CLOSED state without any
         further processing.

      F2 --------------------------------------------------------

         Check the presence of the ACK flag.  If ACK is not set then
         discard the packet and return without any further processing.

         We now assume that the ACK flag was set.  If the AN field value
         was as expected then flush the retransmission queue and inform
         the user with an "Ok" if a buffer has been entirely
         acknowledged.  Another packet containing data may now be sent.
         Return and continue the processing associated with this state.

         We now assume that the ACK flag was set and that the AN field
         value was unexpected.  This is assumed to indicate a duplicate
         acknowledgment.  It is ignored, return and continue the
         processing associated with this state.

      F3 --------------------------------------------------------

         Check the presence of the ACK flag.  If ACK is not set then
         discard the packet and return without any further processing.

         We now assume that the ACK flag was set.  If the AN field value
         was as expected then continue the processing associated with
         this state.

         We now assume that the ACK flag was set and that the AN field
         value was unexpected.  This is ignored, return and continue
         with the processing associated with this state.

      G  --------------------------------------------------------

         This procedure represents the behavior of the CLOSED state of a
         connection.  All incoming packets are discarded.  If the packet
         had the RST flag set take no action.  Otherwise it is necessary
         to build a RST packet.  Since this end is closed the other end
         of the connection has incorrect data about the state of the
         connection and should be so informed.

            If the ACK flag was set then send:

               <SN=received AN><CTL=RST>



Finn                                                           [Page 32]



RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


            If the ACK flag was not set then send:

               <SN=0><AN=received SN+1 modulo 2><CTL=RST, ACK>

         After sending the reset packet return to the current state
         without any further processing.

      H1 --------------------------------------------------------

         Our SYN has been acknowledged.  At this point we are
         technically in the ESTABLISHED state.  Send any initial data
         which is queued to send:

            <SN=received AN><AN=received SN+1 modulo 2><CTL=ACK><DATA>

         Go to the ESTABLISHED state and execute procedure I1 to process
         any data which might be in this packet.

         Any packet not satisfying the