rfc658.txt

RFC 相关的技术文档

D. Crocker (UCLA-NMC)
RFC 658, NIC 31161 (Oct. 25, 1974)
Online file: [ISI]<DCROCKER>NAOLFD.TXT

                  TELNET OUTPUT LINEFEED DISPOSITION

1. Command name and code
   NAOLFD 16 
      (Negotiate About Output Linefeed Disposition)

2. Command meanings
   In the following, we are discussing a simplex connection, as described in 
   the NAOL and NAOP Telnet Options.
      IAC DO NAOLFD 
         The data sender requests or agrees to negotiate about output
         linefeed disposition with the data receiver.  In the case where
         agreement has been reached and in the absence of further
         subnegotiations, the data receiver is assumed to be handling output
         linefeed considerations.
      IAC DON'T NAOLFD 
         The data sender refuses to negotiate about output linefeed
         disposition with the data receiver, or demands a return to the
         unnegotiated default mode.
      IAC WILL NAOLFD 
         The data receiver requests or agrees to negotiate about output
         linefeed disposition with the sender.  In the case where agreement
         has been reached and in the absence of further subnegotiations, the
         data receiver alone is assumed to be handling output linefeed
         considerations.
      IAC WON'T NAOLFD 
         The data receiver refuses to negotiate about output linefeed 
         disposition, or demands a return to the unnegotiated default mode. 
      IAC SB NAOLFD DS <8-bit value> IAC SE
         The data sender specifies, with the 8-bit value, which party should 
         handle output linefeeds and what their disposition should be.  The 
         code for DS is 1.
    IAC SB NAOLFD DR <8-bit value> IAC SE
         The data receiver specifies, with the 8-bit value, which party
         should handle output linefeeds and what their disposition should
         be.  The code for DR is 0.

3. Default
   DON'T NAOLFD/WON'T NAOLFD.
      In the default absence of negotiations concerning which party, data
      under or data receiver, is handling output linefeed considerations,
      neither party is required nor prohibited from handling linefeeds; but
      it is appropriate if at least the data receiver handles them, albeit
      primitively.

4. Motivation for the Option
   Please refer to section 4 of the NAOL and of the NAOLFD Telnet option 
   descriptions.

5. Description of the Option
   The data sender and the data receiver use the 8-bit value along with DS
   and DR SB commands as follows:

      8-bit value         Meaning

      0            Command sender suggests that he alone will handle  
                   linefeeds, for the connection.                     
      1 to 250     Command sender suggests that the other party alone 
                   should handle linefeeds, but suggests that a delay 
                   of the indicated value be used.  The value is the   
                   number of character-times to wait or number of     
                   NULs to insert in the data stream before sending   
                   the next data character.  (See qualifications, below.)
      251          Not allowed, in order to be compatible with        
                   related Telnet options.                            
      252          Command sender suggests that the other party alone 
                   handle linefeeds, but suggests that they be discarded.
      253          Command sender suggests that the other party alone 
                   should handle linefeeds, but suggests that
                   linefeeds be simulated.                            
      254          Command sender suggests that the other party alone 
                   should handle output linefeeds but suggests        
                   waiting for a character to be transmitted (on the  
                   other simplex connection) before sending more      
                   data.  (See qualifications, below.) Note that, due  
                   to the assynchrony of the two simplex connections, 
                   phase problems can occur with this option.         
      255          Command sender suggests that the other party alone 
                   should handle output linefeeds and suggests        
                   nothing about how it should be done.               

   The guiding rules are that: 

      1) if neither data receiver nor data sender wants to handle output 
      linefeeds, the data receiver must do it, and
      2) if both data receiver and data sender want to handle output linefeed 
      disposition, the data sender gets to do it. 

   The reasoning for the former rule is that if neither wants to do it, then
   the default in the NAOLFD option dominates.  If both want to do it, the
   sender, who is presumed to have special knowledge about the data, should
   be allowed to do it, taking into account any suggestions the receiver may
   make.  Simulation is defined as the replacement of the linefeed character
   by new-line (see following) and enough blanks to move the print head (or
   line pointer) to the same lateral position it occupied just prior to
   receiving the linefeed.  To avoid infinite recursion, such simulation is
   allowed only for linefeed characters that are not immediately preceded by
   carriage-returns (that is, part of a Telnet new-line combination).  It is
   assumed that linefeed simulation will be necessary for printers that do
   not have a separate linefeed (like the IBM 2741); in this case,
   end-of-line character padding can be specified through NAOCRD.  Any
   padding (0 < <8-bit-value> < 251) of linefeed characters is to be done
   for ALL linefeed characters.

   NOTE: Delays, controlled by the data sender, must consist of NUL
   characters inserted immediately after the character.  This is necessary
   due to the assynchrony of network transmissions.  Additionally, due to
   the presence of the Telnet end-of-line convention, it may be necessary to
   add carriage-return padding or delay after the associated linefeed (see
   NAOCRD Telnet option).  As with all option negotiations, neither party
   should suggest a state already in effect except to refuse to negotiate;
   changes should be acknowledged; and once refused, an option should not be
   resuggested until "something changes" (e.g., another process starts).  At
   any time, either party can disable further negotiation by giving the
   appropriate WON'T NAOLFD or DON'T NAOLFD command.