rfc2217.txt

< VB高级网络编程技术>>随书源代码第3章,里面有很多有用的例程,希望对大家的开发工作有帮助!

       control option commands.
     IAC DO COM-PORT-OPTION
       The sender of this command is willing to accept com port
       control option commands.
     IAC DONT COM-PORT-OPTION
       The sender of this command refuses to accept com port control
       options commands.

    Typically a client will use WILL and WONT, while an access server
    will use DO and DONT.








Clark                         Experimental                      [Page 5]

RFC 2217          Telnet Com Port Control Option            October 1997


2. Com Port Configuration Commands

   Once DO and WILL have been negotiated, the client may send any of the
   following commands. The client can send these commands at any time
   and multiple times throughout the Telnet session. Each command
   transmitted from the client to the access server must be acknowledged
   once the command has been processed by the access server.  This
   confirmation informs the client of the value set at the access server
   after the processing of the command. This acknowledgment is not used
   to acknowledge the receipt of the command, which is handled at the
   TCP protocol layer.  Its purpose is to inform the client of the value
   in use, which may be different than the value requested in the
   client's command.  For example, the client may request a baud rate
   higher than the access service can provide.  If an acknowledgment is
   not received by the client within a reasonable time (such as twice
   the delay acknowledgment timer), the client may wish to resend the
   command or terminate the session.

   Though the commands may be sent from the client to the access server
   in any sequence, there are sequences which may result in invalid
   configurations for the com port (for example: EVEN parity is only
   valid if the data size is set to less than 8 bits). Thus it is
   recommended that commands be issued in the following sequence:

      1. SET-BAUDRATE
      2. SET-DATASIZE
      3. SET-PARITY
      4. SET-STOPSIZE

     IAC SB COM-PORT-OPTION SIGNATURE <text> IAC SE
       This command may be sent by either the client or the access
       server to exchange signature information.  If the command is
       sent without <text> it is a request from the sender to receive
       the signature text of the receiver.  The text may be a
       combination of any characters.  There is no structure to the
       <text> field.  It may contain manufacturer information, version
       number information, or any other information desired.  If an
       IAC character appears in the text it must be translated to
       IAC-IAC to avoid conflict with the IAC which terminates
       the command.

     IAC SB COM-PORT-OPTION SET-BAUD <value(4)> IAC SE
       This command is sent by the client to the access server to set
       the baud rate of the com port. The value is four octets (4 bytes).
       The value is represented in network standard format.  The value
       is the baud rate being requested.  A special case is the value 0.
       If the value is zero the client is requesting the current baud
       rate of the com port on the access server.



Clark                         Experimental                      [Page 6]

RFC 2217          Telnet Com Port Control Option            October 1997


       Discussion: Though baud rates used today form a very sparse space,
                   and the initial version of the option used an index
                   based baud rate table, after much discussion with a
                   number of groups it has been determined that the
                   actual baud rate should be used.  There are two main
                   reasons. 1) It limits the number of updates to the
                   option as faster baud rates come into use,
                   2) It provides the greatest amount of flexibility
                   in the selection of the baud rates.

     IAC SB COM-PORT-OPTION SET-DATASIZE <value> IAC SE
       This command is sent by the client to the access server to set
       the data bit size. The command can also be sent to query the
       current data bit size. The value is one octet (byte). The value
       is an index into the following value table:

           Value       Data Bit Size
             0           Request Current Data Bit Size
             1           Available for Future Use
             2           Available for Future Use
             3           Available for Future Use
             4           Available for Future Use
             5           5
             6           6
             7           7
             8           8
             9-127       Available for Future Use

       Discussion: There are only eight possible values for the data bit
                   size, only four have ever been used historically and
                   only two are commonly used today. The use of the
                   command-value format is recommended to preserve
                   consistency with other commands. It also reduces the
                   number of commands defined in the protocol, and
                   allows for future expansion.

     IAC SB COM-PORT-OPTION SET-PARITY <value> IAC SE
       This command is sent by the client to the access server to set
       the parity.  The command can also be sent to query the current
       parity. The value is one octet (byte). The value is an index into
       the following value table:

            Value      Parity [1]
              0           Request Current Data Size
              1           NONE
              2           ODD
              3           EVEN
              4           MARK



Clark                         Experimental                      [Page 7]

RFC 2217          Telnet Com Port Control Option            October 1997


              5           SPACE
              6-127       Available for Future Use

       Discussion: There are only five possible values for parity
                   commonly used today. The use of the command-value
                   format is recommended to preserve consistency with
                   other commands.

     IAC SB COM-PORT-OPTION SET-STOPSIZE <value> IAC SE
       This command is sent by the client to the access server to set
       the number of stop bits. The command can also be sent to query
       the current stop bit size. The value is one octet (byte). The
       value is an index into the following value table:

           Value      Stop Bit Size
             0           Request Current Data Size
             1           1
             2           2
             3           1.5
             4-127       Available for Future Use

       Discussion: Stop bit 1.5 is supported by most com port hardware
                   only if data size is set to 5 bits. It is not
                   commonly used.

3. Special Com Port Control Commands

   The client can send this command to the access server at any time
   and multiple times throughout the Telnet session. Each command
   transmitted from the client to the access server is acknowledged
   with a confirmation of the command and the actual value set. The
   client should expect a response within a reasonable time (such as
   twice the delay acknowledgment timer). The client may wish to
   resend any command which is not acknowledged or terminate the
   session.

     IAC SB COM-PORT-OPTION SET-CONTROL <value> IAC SE
       This command is sent by the client to the access server to set
       special com port options. The command can also be sent to query
       the current option value. The value is one octet (byte). The
       value is an index into the following value table:

           Value      Control Commands
             0           Request Com Port Flow Control Setting
                           (outbound/both)
             1           Use No Flow Control (outbound/both)
             2           Use XON/XOFF Flow Control (outbound/both)
             3           Use HARDWARE Flow Control (outbound/both)



Clark                         Experimental                      [Page 8]

RFC 2217          Telnet Com Port Control Option            October 1997


             4           Request BREAK State
             5           Set BREAK State ON
             6           Set BREAK State OFF
             7           Request DTR Signal State
             8           Set DTR Signal State ON
             9           Set DTR Signal State OFF
            10           Request RTS Signal State
            11           Set RTS Signal State ON
            12           Set RTS Signal State OFF
            13           Request Com Port Flow Control Setting (inbound)
            14           Use No Flow Control (inbound)
            15           Use XON/XOFF Flow Control (inbound)
            16           Use HARDWARE Flow Control (inbound)
            17           Use DCD Flow Control (outbound/both)
            18           Use DTR Flow Control (inbound)
            19           Use DSR Flow Control (outbound/both)
            20-127       Available for Future Use

       Discussion: Flow control options were divided into inbound and
                   outbound to take full advantage of existing
                   programming interfaces and access server
                   capabilities.

       Discussion: The outbound values should set flow control for both
                   outbound and inbound.  If inbound is to be, or can
                   be, set separately it should be done after the
                   setting of the outbound value.

       Discussion: If the access server is not able to set inbound flow
                   control differently from the outbound flow control,
                   it should ignore the inbound flow control commands
                   and set the flow control option based on the outbound
                   flow control commands only.

     IAC SB COM-PORT-OPTION SET-LINESTATE-MASK <value> IAC SE
       This command is sent by the client to the access server to set a
       bit mask for the sending of the NOTIFY-LINESTATE option (see
       section 4).  When the LINESTATE changes on the access server, the
       access server will "AND" the new LINESTATE with the LINESTATE-
       MASK.  If the result is not zero, the access server will send the
       result of the "AND" as the value in a NOTIFY-LINESTATE com port
       option. If more than one bit satisfies the LINESTATE-MASK, only
       one NOTIFY-LINESTATE, with all the satisfying bits, will be sent
       to the client.  The SET-LINESTATE-MASK may be any combination of
       bits as listed below.  These are the same bit values used in the
       NOTIFY-LINESTATE option.  The SET-LINESTATE-MASK values are based
       on the most popular UART (com port control chip) in use [1].




Clark                         Experimental                      [Page 9]

RFC 2217          Telnet Com Port Control Option            October 1997


           Bit Position     Value     Meaning
              7              128         Time-out Error
              6               64         Transfer Shift Register Empty
              5               32         Transfer Holding Register Empty
              4               16         Break-detect Error
              3                8         Framing Error
              2                4         Parity Error
              1                2         Overrun Error
              0                1         Data Ready

       Discussion: The SET-LINESTATE-MASK value of 0 will prevent the
                   access server from sending NOTIFY-LINESTATE options
                   to the client.

       Discussion: The SET-LINESTATE-MASK value of 255 will allow the
                   access server to send a NOTIFY-LINESTATE option to