rfc2217.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

                   the client each time the LINESTATE changes on the
                   access server.

       Discussion: The initial LINESTATE-MASK at the access server is 0.

       Discussion: The client does not have to send a new
                   SET-LINESTATE-MASK after receiving a NOTIFY-
                   LINESTATE.  The LINESTATE-MASK on the access server
                   is retained until set by the client or reset at the
                   start of a new Telnet session.

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










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RFC 2217          Telnet Com Port Control Option            October 1997


           Bit Position     Value     Meaning
              7              128        Receive Line Signal Detect
                                        (also known as Carrier Detect)
              6               64        Ring Indicator
              5               32        Data-Set-Ready Signal State
              4               16        Clear-To-Send Signal State
              3                8        Delta Receive Line Signal Detect
              2                4        Trailing-edge Ring Detector
              1                2        Delta Data-Set-Ready
              0                1        Delta Clear-To-Send

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

       Discussion: The SET-MODEMSTATE-MASK value of 255 will allow the
                   access server to send a NOTIFY-MODEMSTATE option to
                   the client each time the MODEMSTATE changes on the
                   access server.

       Discussion: The initial MODEMSTATE-MASK at the access server
                   is 255.

       Discussion: The client does not have to send a new
                   SET-MODEMSTATE-MASK after receiving a NOTIFY-
                   MODEMSTATE.  The MODEMSTATE-MASK on the access server
                   is retained until set by the client or reset at the
                   start of a new Telnet session.

     IAC SB COM-PORT-OPTION PURGE-DATA <value> IAC SE
       This command is sent by the client to the access server to
       instruct the access server to immediately clear all data from the
       buffer or buffers referenced by the value.  The value is one
       octet (byte).  The value is an index into the following value
       table:

           Value      Purge Data Buffer
             0           Available for Future Use
             1           Purge access server receive data buffer
             2           Purge access server transmit data buffer
             3           Purge both the access server receive data
                         buffer and the access server transmit data
                         buffer
             4-127       Available for Future Use







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RFC 2217          Telnet Com Port Control Option            October 1997


4. Notification of Com port and Modem Line Changes

   The access server can send these commands to the client any time
   and multiple times throughout the Telnet session. The access
   server should send the appropriate command to the client as soon
   as the com port or modem line changes occurs.  The client does
   not issue a response to these commands.

     IAC SB COM-PORT-OPTION NOTIFY-LINESTATE <value> IAC SE
       The value is one octet (byte). The value is a bit level
       composition made up from the value table below. Multiple bit
       values may be set in a single transmission. The values are based
       on the most popular UART (com port control chip) in use [1].

           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 LINESTATE is the line state of the UART on
                   the access server.

     IAC SB COM-PORT-OPTION NOTIFY-MODEMSTATE <value> IAC SE
       The value is one octet (byte). The value is a bit level
       composition made up from the value table below. Multiple bit
       values may be set in a single transmission. The values are based
       on the most popular UART (com port control chip) in use [1].

           Bit Position     Value     Meaning
              7              128        Receive Line Signal Detect
                                        (also known as Carrier Detect)
              6               64        Ring Indicator
              5               32        Data-Set-Ready Signal State
              4               16        Clear-To-Send Signal State
              3                8        Delta Receive Line Signal Detect
              2                4        Trailing-edge Ring Detector
              1                2        Delta Data-Set-Ready
              0                1        Delta Clear-To-Send







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RFC 2217          Telnet Com Port Control Option            October 1997


5. Flow Control

   The client and/or access server can send these commands any time and
   multiple times throughout the Telnet session.

     IAC SB COM-PORT-OPTION FLOWCONTROL-SUSPEND IAC SE
       The sender of this command is requesting that the receiver
       suspend transmission of both data and commands until the
       FLOWCONTROL-RESUME is transmitted by the sender.

     IAC SB COM-PORT-OPTION FLOWCONTROL-RESUME IAC SE
       The sender of this command is requesting that the receiver resume
       transmission of both data and commands.

       Discussion: Established Telnet sessions are initially in a
                   resume state between the client and the access server
                   and the access server and the client.  There is no
                   need to send the resume command during session
                   initialization.

       Discussion: Multiple concurrent suspend commands may be sent.
                   Secondary suspend commands can be ignored.
                   Transmission will resume with the sending of a single
                   resume command.

       Discussion: The flow control option is designed to handle client
                   to access server flow control for the Telnet session.
                   This option has been added in deference to RFC 1372:
                   Telnet Remote Flow Control Option [2].  RFC 1372 uses
                   a simple character XON/XOFF technology to implement
                   flow control.  This can lead to two problems.  First,
                   the flow control characters may be valid data values.
                   Second, the flow control characters may be used for
                   end to end flow control (client application to remote
                   dial up service).

6. Security Considerations

   There are two security issues to discuss; authentication and
   resetting resources.

   Authentication can follow either the Kerberos authentication protocol
   established in RFC 1411 [3] or the SPX authentication protocol
   established in RFC 1412 [4].

   Once the Telnet session between the client and the access server has
   been terminated, the access server should ensure the connection to
   the remote service is disconnected and the com port geometry (baud



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RFC 2217          Telnet Com Port Control Option            October 1997


   rate, data size, stop bits, parity, and flow control) is reset to a
   factory or administrator defined configuration.  This ensures the com
   port is in a known state and ready to receive the next client
   session.  This will make operations more predicable and avoid
   problems which might occur from starting a new session with random
   com port configurations.

7. Author's Address

  Glen Clark, Software Architect
  Cisco Systems, Inc.
  170 West Tasman Drive
  San Jose, CA  96134
  USA

  EMail:      [e-mail]
  WEB:        www.cisco.com

8. Reference Section

   [1]  Joe Campbell. C Programmer's Guide to Serial Communications,
        Second Edition. Indianapolis: SAMS Publishing, 1993. 213-224.

   [2]  Hedrick, C., and D. Borman, "Telnet Remote Flow Control Option",
        RFC 1372, Cray Research, Inc., October 1992.

   [3]  Borman, D., "Telnet Authentication: Kerberos Version 4",
        RFC 1411, Cray Research, Inc., January 1993.

   [4]  Alagappan, K., "Telnet Authentication: SPX",
        RFC 1412, Digital Equipment Corporation, January 1993.

   [5]  D. E. Comer and David Stevens.  Internetworking with TCP/IP,
        Volume III.  Prentice Hall, 1993.

   [6]  Andrew Margolis. The FAX Modem Sourcebook.  John Wiley & Sons.
        1995.














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