rfc929.txt

RFC 的详细文档！

            TCP    The code for the protocol TCP
            A      Indicates Active Begin
            ISIA   The name of a Host at USC-ISI
            9      Mediation Level 9:  Full OPE mediation
            N      Non-blocking transmit
            23     Destination Telnet Port
            ,,     skip  over parameters  (Local Address Secondary,
                   Begin Timeout Interval)
            N0     Type of Service Advice:  No special Advice,
                   Normal Precedence
            S      Flow Control Advice: use small blocks

         This command will cause the OPE to invoke the TCP interpreter
         to generate the initial SYN packet to the well-known Telnet
         socket on Host ISIA.  It also informs the OPE to do all TCP
         related processing via the Mediation Level, accepts default


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RFC 929                                                    December 1984
Proposed Host-Front End Protocol


         Local Address parameters, and sets the Begin Timeout Interval
         to infinity.  The precedence of the TCP connection is Normal,
         and the TCP interpreter is informed that the data stream will
         consist of primarily small blocks.

      Notes to the Implementor

         Response 203 might seem silly to some readers, but it's there
         in case somebody goofed in using the Channel Layer.

   Transmit

      Purpose of the Transmit Command

         The purpose of the Transmit command is to permit the process in
         the Host to send data using an off-loaded protocol interpreter
         in the OPE, and also to permit the OPE to deliver data received
         from the network destined for the process in the Host.  The
         Transmit command is particularly relevant to connection and
         stream type protocols, although it has applications for
         connectionless protocols as well.  After the Begin command is
         issued successfully and the proper Response received, Transmit
         commands can be issued on the given channel.  The semantics of
         the Transmit command depend on whether it was issued by the
         Host or the OPE.

         - If the Host issues the Transmit command, a process in the
         Host wishes to send the data to the destination specified to
         the off-loaded protocol interpreter that was established
         (typically) by a previous Begin command on the given H-FP
         channel.

         - If the OPE issues the command, the OPE has received data
         destined for a process in the Host from a connection or stream
         supported by the off-loaded protocol that was established by a
         previous Begin command on the given H-FP channel.

      Parameters of the Transmit Command

         The Transmit command has one parameter associated with it. It
         is an optional parameter, to temporarily override the response
         discipline for this particular transmit command. Some protocols
         may have protocol-idiosyncratic parameters as well.  The
         transmit command also has data associated with it.  All
         parameters must precede the data to be transmitted.




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RFC 929                                                    December 1984
Proposed Host-Front End Protocol


      Response Discipline Override

         The Response Discipline Override parameter indicates the
         desired response discipline for that individual Transmit
         Command, overriding the default response discipline.  A single
         ASCII character is used to indicate the desired discipline.
         The character "N" indicates that this Transmit command should
         not block, and should return a response as soon as the data is
         given to the protocol interpreter in the OPE. The character "B"
         indicates that this Transmit command should block, meaning that
         a response should not be generated until the data has been sent
         to the destination.  The default value of this parameter is the
         currently defined Transmit Command response discipline.  The
         use of this parameter does not alter the currently defined
         Transmit command response discipline; the default is changed
         with the Condition command.  The control flag for this
         parameter is -rd.

      Protocol-Idiosyncratic Parameters

         Any other parameters to the Transmit command are
         protocol-idiosyncratic. That is, each protocol that is
         off-loaded has a set of these parameters, which are documented
         with a description of the off-loaded protocol.  The default
         value for these parameters is NULL, unless otherwise specified
         by a particular off-loaded protocol.  The control flag for this
         set of parameters is -pi, which identifies the first
         protocol-idiosyncratic parameters.  Control flags for other
         protocol-idiosyncratic parameters must be defined for each
         off-loaded protocol.

      Responses

         The following responses for the Transmit command have been
         identified:

            000    Transmit Command completed successfully
            201    Transmit Command not appropriate
            300    Problem with multiple chunks
            301    Syntax problem with Transmit Command
            302    Invalid Transmit Command Response Discipline
            401    Protocol Interpreter in OPE not responding
            402    Failure in remote protocol interpreter
            403    Failed; insufficient protocol interpreter resources
            501    Failed; insufficient OPE resources
            601    Request violates security policy



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RFC 929                                                    December 1984
Proposed Host-Front End Protocol


         Additionally, protocol-idiosyncratic responses will be defined
         for each off-loaded protocol.

      Example of Transmit Command

         The transmit command is used in TCP to provide the TCP write
         call.  An example of such a transmit command would be:

            C TR N <nl> <DATA>

         Where N indicates non-blocking transmission discipline, <nl> is
         the required command-ending newline, and <DATA> is presumed to
         be the user's data that is to be transmitted.

      Notes to the Implementor

         If you get a 403 or a 501 response and have sent a multiple
         chunk it probably makes sense to try a single chunk; if you've
         sent a single chunk, it makes sense to wait a while and try
         again a few times before giving up on the stream/channel.

   Condition

      Purpose of the Condition Command

         The primary purpose of the Condition command is to permit a
         process to alter the characteristics that were originally set
         up with the Begin command. (That is, "condition" is a verb.)
         These characteristics include the addresses, the mediation
         level, the type of service, and the flow control parameters
         from Begin. They may also include protocol-idiosyncratic
         characteristics. (Although Condition is usually thought of as a
         Host->OPE command, it may also be used OPE->Host in some
         contexts.)

         Condition is a generic command that may find little use in some
         off-loaded protocols.  In others, only some of the parameters
         identified may make sense.  For example, changing the
         destination address of a TCP connection involves closing one
         connection and opening another.  Consequently, in may make more
         sense to first issue an End command, and then a Begin with the
         new address.  In other protocols, such as IP or UDP, changing
         the address on each datagram would be a perfectly reasonable
         thing to do.





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RFC 929                                                    December 1984
Proposed Host-Front End Protocol


      Parameters of the Condition Command

         The Condition command has the same parameters as the Begin
         command.  Any parameters expressed in a Condition command
         indicate the new values of the characteristics to be altered;
         all parameters not expressed retain the current value.

         Although it is possible to express the change of any of the
         characteristics originally set up in the Begin command using
         the Condition command, there are some characteristics that do
         not make sense to alter, at least for some protocols. For
         example, once a connection is opened, it does not make much
         sense to change the Foreign Address Primary or Secondary
         Components.  Doing so is inconsistent with current versions of
         TCP, and would require the closing of the existing connection
         and opening a new one to another address.  Earlier versions of
         TCP did permit connections to be moved.  If a protocol that
         provided such a feature was implemented in the OPE, the
         changing the Secondary Address Components would be a reasonable
         thing to do.

      Responses

         The responses to the Condition command are the same as those to
         the Begin command.

      Example of Condition Command

         The Condition Command can be quite complex, and can be used for
         many purposes.  One conceived use of the condition command
         would be to change the type of service advice associated with
         the channel. An example of this (which also demonstrates the
         ability to skip parameters) is:

            C -ts T <nl>

         which causes the offloaded PI associated with the current
         channel to attempt to achieve high throughput (in its use of
         the comm subnet(s) in play).

      Notes to the Implementor








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RFC 929                                                    December 1984
Proposed Host-Front End Protocol


   Signal

      Purpose of Signal Command

         The purpose of the Signal Command (implicitly at least) is to
         permit the transfer of out-of-band signals or information
         between the Host and the OPE, in order to utilize (explicitly)
         out-of-band signaling services of the off-loaded protocol. The
         semantics of the Signal command depend upon whether it was
         issued by the Host or the OPE.

         - If the Signal command was issued by the Host, it means a
         process in the Host desires to send out-of-band data or an
         out-of-band signal.

         - If the Signal command was issued by the OPE, it means
         out-of-band data or an out-of-band signal arrived for the
         process associated with the channel in the Host.

      Parameters of the Signal Command

         The basic usage of the Signal command is with no parameters,
         which sends or reports the receipt of an out-of-band