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.

   is a slightly more detailed look at the allowed transitions which
   occur between states.  Finally a detailed discussion of the behavior
   of each state is given.

   5.1. Protocol States

      The states used to describe this protocol are:

         LISTEN

            This state represents waiting for a connection from the
            other end of the link.

         SYN-SENT

            This represents waiting for a matching connection request
            after having sent a connection request.

         SYN-RECEIVED

            This represents waiting for a confirming connection request
            acknowledgment after having both received and sent a
            connection request.





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RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


         ESTABLISHED

            This state represents a connection fully opened at both
            ends.  This is the normal state for data transfer.

         FIN-WAIT

            In this state one is waiting for a connection termination
            request from the other end of the connection and an
            acknowledgment of a termination request previously sent.

         LAST-ACK

            This end of the connection has seen and acknowledged a
            termination request from the other end.  This end has
            responded with a termination request of its own and is now
            expecting an acknowledgment of that request.

         CLOSING

            This represents waiting for an acknowledgment of a
            connection termination request.

         TIME-WAIT

            This represents waiting for enough time to pass to be sure
            that the other end of the connection received the
            acknowledgment of its termination request.

         CLOSED

            A fictional state which represents a completely terminated
            connection.  If either end of a connection is in this state
            it will neither send nor receive data or control packets.















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RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


   5.2. State Transitions

      This section describes events which cause the protocol to depart
      from its current state.  A brief mention of each state is
      accompanied by a list of departure events and to which state the
      protocol goes as a result of those events.  Departures due to the
      presence of a RST flag are not shown.

      5.2.1. LISTEN

         This is a request to listen for any connection from the other
         end of the link.  In this state, no packets are sent.  The
         connection may be thought of as half-open.  A STATUS request
         will return to the caller this information.

         Arrived at from the CLOSED state in response to a passive OPEN.
         In a passive OPEN no packets are sent, the interface is waiting
         for the initiation of a connection from the other end of the
         link.  Also this state can be reached in certain cases in
         response to an RST connection reset request.

         Departures

            - A CLOSE request is made by the user.  Delete the half-open
              TCB and go to the CLOSED state.

            - A packet arrives with the SYN flag set.  Retrieve the
              sender's MDL he placed into the LENGTH field.  Set AN to
              be received SN+1 modulo 2.  Build a response packet with
              SYN, ACK set.  Choose your MDL and place it into the
              LENGTH octet.  Choose your initial SN, place in AN.  Send
              this packet and go to the SYN-RECEIVED state.

      5.2.2. SYN-SENT

         Arrived at from the CLOSED state in response to a user's active
         OPEN request.

         Departures

            - A CLOSE request is made by the user.  Delete the TCB and
              go to the CLOSED state.

            - A packet arrives with the SYN flag set.  Retrieve the
              sender's MDL he placed into the LENGTH field.  Set AN to




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RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


              be received SN+1 modulo 2.  Build a response packet with
              ACK set, place in AN.  Send this packet and go to the
              SYN-RECEIVED state.

            - A packet arrives with the SYN, ACK flags set.  Retrieve
              the sender's MDL he placed into the LENGTH field.  Set AN
              to be received SN+1 modulo 2.  Build a response packet
              with ACK set.  Set SN to be SN+1 modulo 2, place SN and AN
              into the header.  Remembering the other end's MDL, build
              data portion of packet.  Send this packet and go to the
              ESTABLISHED state.

      5.2.3. SYN-RECEIVED

         Arrived at from the LISTEN and SYN-SENT states in response to
         an arriving SYN packet.

         Departures

            - A CLOSE request is made by the user.  Create a packet with
              FIN set.  Send it and go to the FIN-WAIT state.

            - A packet arrives with the ACK flag set.  This packet
              acknowledges a previous SYN packet.  Go to the ESTABLISHED
              state.  The TCB should now note the connection is fully
              opened.

            - A packet arrives with the FIN flag set.  The other end has
              decided to close the connection.  Create a packet with
              FIN, ACK set.  Send it and go to the LAST-ACK state.

      5.2.4. ESTABLISHED

         This state is the normal state for a connection.  Data packets
         may be exchanged in both directions (MDL allowing).  It is
         arrived at from the SYN-RECEIVED and SYN-SENT states in
         response to the completion of connection initiation.

         Departures

            - In response to a CLOSE request from the user.  Set AN to
              be most recently received SN+1 modulo 2.  Build a packet
              with FIN set.  Set SN to be SN+1 modulo 2, place SN and AN
              into the header and send the packet.  Go to the FIN-WAIT
              state.

            - A packet containing a FIN is received.  Set AN to be


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RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


              received SN+1 modulo 2.  Build a response packet with both
              FIN and ACK set.  Set SN to be SN+1 modulo 2, place SN and
              AN into the header.  No data portion is built.  Send this
              packet and go to the LAST-ACK state.

      5.2.5. FIN-WAIT

         Arrived at from either the SYN-RECEIVED state or from the
         ESTABLISHED state.  In both cases the user had requested a
         CLOSE of the connection and a packet with a FIN was sent.

         Departures

            - A FIN, ACK packet is received which acknowledges the FIN
              just sent.  Go to the TIME-WAIT state.

            - A FIN packet is received which indicates the other end of
              the connection has simultaneously decided to close.  Set
              AN=received SN+1 modulo 2, and SN=SN+1 modulo 2.  Send a
              response packet with the ACK set.  Go to the CLOSING
              state.

      5.2.6. LAST-ACK

         Arrived at from the ESTABLISHED and SYN-RECEIVED states.

         Departures

            - An ACK is received for the last packet sent which was a
              FIN.  Delete the TCB and go to the CLOSED state.

      5.2.7. CLOSING

         Arrived at from the FIN-WAIT state.

         Departures

            - An ACK is received for the last packet sent which was a
              FIN.  Go to the TIME-WAIT state.

      5.2.8. TIME-WAIT

         Arrived at from the FIN-WAIT and CLOSING states.






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RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


         Departures

            - This states waits until 2*SRTT time has passed.  It then
              deletes the TCB associated with the connection and goes to
              the CLOSED state.

      5.2.9. CLOSED

         This state can be arrived at for a number of reasons: 1) while
         in the LISTEN state the user requests a CLOSE, 2) while in the
         SYN-SENT state the user requests a CLOSE, 3) while in the
         TIME-WAIT state the 2*SRTT time period has elapsed, and 4)
         while in the LAST-ACK state an arriving packet has an ACK of
         the previously sent FIN packet.

         In this state no data is read or sent over the link.  To leave
         this state requires an outside request to open a new
         connection.

         Departures

            - User requests an active OPEN.  Create a packet with SYN
              set.  Choose your MDL and place it into the LENGTH octet.
              Choose your initial SN.  AN is immaterial.  Send this
              packet and go to the SYN-SENT state.  The TCB for this
              connection is created.  The connection may be thought of
              as half-open.  A STATUS request will return to the caller
              this information.

            - User requests a passive OPEN.  The TCB for this connection
              is created.  The connection may be thought of as
              half-open.  A STATUS request will return to the caller
              this information.  Go to the LISTEN state.
















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RFC 916                                                     October 1984
Reliable Asynchronous Transfer Protocol


   5.3. State Behavior

      This section discusses in detail the behavior of each state in
      response to the arrival of a packet.  In what follows a packet is
      not considered to have arrived until it has passed a number of
      tests (see the chapter entitled: Packet Reception).

      The method chosen to describe state behavior is tabular.  Each
      state is listed opposite a sequence of named procedures to execute
      whenever a packet has arrived.

      STATE                BEHAVIOR
      =============+========================
      LISTEN       |  A
      -------------+------------------------
      SYN-SENT     |  B
      -------------+------------------------
      SYN-RECEIVED |  C1  D1  E  F1  H1
      -------------+------------------------
      ESTABLISHED  |  C2  D2  E  F2  H2  I1
      -------------+------------------------
      FIN-WAIT     |  C2  D2  E  F3  H3
      -------------+------------------------
      LAST-ACK     |  C2  D3  E  F3  H4
      -------------+------------------------
      CLOSING      |  C2  D3  E  F3  H5
      -------------+------------------------
      TIME-WAIT    |  D3  E  F3 H6
      -------------+------------------------
      CLOSED       |  G
      -------------+------------------------

      For example, in the ESTABLISHED state the arrival of a packet
      causes procedure C2 to be executed, then D2, then E, F2, H2, and
      finally I1.  Any procedure may terminate the processing which
      occurs or cause a state change.  Note that these procedures are
      executed in sequence, first C2, then D2, etc.  The time ordering
      cannot be mixed.

      The particular actions associated with each procedure are now
      described.