rfc1644.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

           does not contain an ACK bit.

      According to the state model of the basic TCP specification [STD-
      007], the server side must explicitly issued a passive OPEN call,
      creating a TCB in LISTEN state, before an initial SYN may be
      accepted.  To accommodate truncation of TIME-WAIT state within
      this model, it is necessary to add the five "I-states" shown in
      Figure 10.  The I-states are:  LISTEN-LA, LISTEN-LA*, LISTEN-CL,
      LISTEN-CL*, and LISTEN-TW.  These are 'bridge states' between two
      successive the state diagrams of two successive incarnations.
      Here D is the duration of the previous connection, i.e., the
      elapsed time since the connection opened.  The transitions labeled
      with lower-case letters are taken from Figure 8.

      Fortunately, many TCP implementations have a different user
      interface model, in which the use can issue a generic passive open
      ("listen") call; thereafter, when a matching initial SYN arrives,
      a new TCB in LISTEN state is automatically generated.  With this
      user model, the I-states of Figure 10 are unnecessary.

      For example, suppose an initial SYN segment arrives for a
      connection that is in LAST-ACK state.  If this segment carries a
      CC option and if SEG.CC is greater than TCB.CCrecv in the existing
      TCB, the "q" transition shown in Figure 10 can be made directly
      from the LAST-ACK state.  That is, the previous TCB is processed
      as if an ACK(FIN) had arrived, causing the user to be notified of
      a successful CLOSE and the TCB to be deleted.  Then processing of
      the new SYN segment is repeated, using a new TCB that is generated
      automatically.  The same principle can be used to avoid
      implementing any of the I-states.



















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RFC 1644                    Transaction/TCP                    July 1994


 ______________________________
| P: Passive OPEN /            |
|                              |
| Q: Rcv SYN, special TAO test |                     d'|     d|
|     (see text) / Delete TCB, |    ________        ___V____  |
|     create TCB, snd SYN      |   |LISTEN- |  P   | LAST-  | |
|                              |   |   LA*  |<-----|  ACK*  | |
| Q': (same as Q) if D < MSL   |   |________|      |________| |
|                              |    |     |            |      |
| R: Rcv ACK(FIN) / Delete TCB,|   Q|   c'|          c'|      |
|     create TCB               |    |     |            |      |
|                              |    |  ___V____        V______V
| S': Active OPEN if D < MSL / |    | |LISTEN- |  P   | LAST-  |
|     Delete TCB, create TCB,  |    | |  LA    |<-----|   ACK  |
|     snd SYN.                 |    | |________|      |________|
|______________________________|    |  |     |            |
                                    | Q|    R|           f|
         ________        ________   |  |     |            |
   e''' |        |  P   |LISTEN- |  |  |     V            V
   ---->|CLOSING*|----->|   CL*  |  |  |   LISTEN       CLOSED
        |________|      |________|  |  |
             |            |   Q|    |  |
           c'|          c'|    V    V  V
             |            |   ESTABLISHED*
         ____V___         V_______
    e'' |        |  P    |LISTEN- |
   ---->|CLOSING |------>|   CL   |
        |________|       |________|
             |           R|     Q|
            f|            V      V
             |         LISTEN   ESTABLISHED*
         ____V___                _________
     e  |TIME-   |  P           | LISTEN- |
   ---->|   WAIT |------------->|    TW   |
        |________|              |_________|
        /     |                  |    |  |
     S'/     T|                 T|  Q'|  |S'
      |  _____V_      h     _____V__  |  V
      | |        |-------->|        | |  SYN-SENT
      | | CLOSED |<--------| LISTEN | |
      | |________|   ------|________| |
      |   |        /        |   j|    |
      |  a|     a'/        i|    V    V
      |   |      /          |   ESTABLISHED*
      V   V     V           V
        SYN-SENT           ...

             Figure 10: I-States for TIME-WAIT Truncation



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RFC 1644                    Transaction/TCP                    July 1994


   3.4  T/TCP Processing Rules

      This section summarizes the rules for sending and processing the
      T/TCP options.

      INITIALIZATION

         I1:  All cache entries cache.CC[*] and cache.CCsent[*] are
              undefined (zero) when a host system initializes, and CCgen
              is set to a non-zero value.

         I2:  A new TCB is initialized with TCB.CCrecv = 0 and
              TCB.CCsend = current CCgen value; CCgen is then
              incremented.  If the result is zero, CCgen is incremented
              again.


      SENDING SEGMENTS

         S1:  Sending initial <SYN> Segment

              An initial <SYN> segment is sent with either a CC option
              or a CC.NEW option.  If cache.CCsent[fh] is undefined or
              if TCB.CCsend < cache.CCsent[fh], then the option
              CC.NEW(TCB.CCsend) is sent and cache.CCsent[fh] is set to
              zero.  Otherwise, the option CC(TCB.CCsend) is sent and
              cache.CCsent[fh] is set to CCsend.

         S2:  Sending <SYN,ACK> Segment

              If the sender's TCB.CCrecv is non-zero, then a <SYN,ACK>
              segment is sent with both a CC(TCB.CCsend) option and a
              CC.ECHO (TCB.CCrecv) option.

         S3:  Sending Non-SYN Segment

              A non-SYN segment is sent with a CC(TCB.CCsend) option if
              the TCB.CCrecv value is non-zero, or if the state is SYN-
              SENT or SYN-SENT* and cache.CCsent[fh] is non-zero (this
              last is required to send CC options in the segments
              following the first of a multi-segment request message;
              see segment #2 in Figure 6).

      RECEIVING INITIAL <SYN> SEGMENT

         Suppose that a server host receives a segment containing a SYN
         bit but no ACK bit in LISTEN, SYN-SENT, or SYN-SENT* state.




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         R1.1:If the <SYN> segment contains a CC or CC.NEW option,
              SEG.CC is stored into TCB.CCrecv of the new TCB.

         R1.2:If the segment contains a CC option and if the local cache
              entry cache.CC[fh] is defined and if
              SEG.CC > cache.CC[fh], then the TAO test is passed and the
              connection is half-synchronized in the incoming direction.
              The server host replaces the cache.CC[fh] value by SEG.CC,
              passes any data in the segment to the user, and processes
              a FIN bit if present.

              Acknowledgment of the SYN is delayed to allow piggybacking
              on a response segment.

         R1.3:If SEG.CC <= cache.CC[fh] (the TAO test has failed), or if
              cache.CC[fh] is undefined, or if there is no CC option
              (but possibly a CC.NEW option), the server host proceeds
              with normal TCP processing.  If the connection was in
              LISTEN state, then the host executes a 3-way handshake
              using the standard TCP rules.  In the SYN-SENT or SYN-
              SENT* state (i.e., the simultaneous open case), the TCP
              sends ACK(SYN) and enters SYN-RECEIVED state.

         R1.4:If there is no CC option (but possibly a CC.NEW option),
              then the server host sets cache.CC[fh] undefined (zero).
              Receiving an ACK for a SYN (following application of rule
              R1.3) will update cache.CC[fh], by rule R3.

         Suppose that an initial <SYN> segment containing a CC or CC.NEW
         option arrives in an I-state (i.e., a state with a name of the
         form 'LISTEN-xx', where xx is one of TW, LA, L8, CL, or CL*):

         R1.5:If the state is LISTEN-TW, then the duration of the
              current connection is compared with MSL.  If duration >
              MSL then send a RST:

                <SEQ=0><ACK=SEG.SEQ+SEG.LEN><CTL=RST,ACK>

              drop the packet, and return.

         R1.6:Perform a special TAO test: compare SEG.CC with
              TCB.CCrecv.

              If SEG.CC is greater, then processing is performed as if
              an ACK(FIN) had arrived:  signal the application that the
              previous close completed successfully and delete the
              previous TCB.  Then create a new TCB in LISTEN state and
              reprocess the SYN segment against the new TCB.



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RFC 1644                    Transaction/TCP                    July 1994


              Otherwise, silently discard the segment.

      RECEIVING <SYN,ACK> SEGMENT

         Suppose that a client host receives a <SYN,ACK> segment for a
         connection in SYN-SENT or SYN-SENT* state.

         R2.1:If SEG.ACK is not acceptable (see [STD-007]) and
              cache.CCsent[fh] is non-zero, then simply drop the segment
              without sending a RST.  (The new SYN that the client is
              (re-)transmitting will eventually acknowledge any
              outstanding data and FIN at the server.)

         R2.2:If the segment contains a CC.ECHO option whose SEG.CC is
              different from TCB.CCsend, then the segment is
              unacceptable and is dropped.

         R2.3:If cache.CCsent[fh] is zero, then it is set to TCB.CCsend.

         R2.4:If the segment contains a CC option, its SEG.CC is stored
              into TCB.CCrecv of the TCB.

      RECEIVING <ACK> SEGMENT IN SYN-RECEIVED STATE

         R3.1:If a segment contains a CC option whose SEG.CC differs
              from TCB.CCrecv, then the segment is unacceptable and is
              dropped.

         R3.2:Otherwise, a 3-way handshake has completed successfully at
              the server side.  If the segment contains a CC option and
              if cache.CC[fh] is zero, then cache.CC[fh] is replaced by
              TCB.CCrecv.

      RECEIVING OTHER SEGMENT

         R4:  Any other segment received with a CC option is
              unacceptable if SEG.CC differs from TCB.CCrecv.  However,
              a RST segment is exempted from this test.

      OPEN REQUEST

         To allow truncation of TIME-WAIT state, the following changes
         are made in the state diagram for OPEN requests (see Figure
         10):

         O1.1:A new passive open request is allowed in any of the
              states: LAST-ACK, LAST-ACK*, CLOSING, CLOSING*, or TIME-
              WAIT.  This causes a transition to the corresponding I-



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RFC 1644                    Transaction/TCP                    July 1994


              state (see Figure 10), which retains the previous state,
              including the retransmission queue and timer.

         O1.2 A new active open request is allowed in TIME-WAIT or
              LISTEN-TW state, if the elapsed time since the current
              connection opened is less than MSL.  The result is to
              delete the old TCB and create a new one, send a new SYN
              segment, and enter SYN-SENT or SYN-SENT* state (depending
              upon whether or not the SYN segment contains a FIN bit).

      Finally, T/TCP has a provision to improve performance for the case
      of a client that "sprays" transactions rapidly using many
      different server hosts and/or ports.  If TCB.CCrecv in the TCB is
      non-zero (and still assuming that the connection duration is less
      than MSL), then the TIME-WAIT delay may be set to min(K*RTO,
      2*MSL).  Here RTO is the measured retransmission timeout time and
      the constant K is currently specified to be 8.

   3.5  User Interface

      STD-007 defines a prototype user interface ("transport service")
      that implements the virtual circuit service model [STD-007,
      Section 3.8].  One addition to this interface in required for
      transaction processing: a new Boolean flag "end-of-file" (EOF),
      added to the SEND call.  A generic SEND call becomes:

        Send

          Format:  SEND (local connection name, buffer address,
               byte count, PUSH flag, URGENT flag, EOF flag [,timeout])

      The following text would be added to the description o