RFC0652: Telnet output carriage-return disposition option






Request for Comments:  652                   D. Crocker (UCLA-NMC)
                                                        25 Oct. 74
NIC #31155
Online file:  [ISI]<DCROCKER>NAOCRD.TXT




      Telnet Output Carriage-Return Disposition Option



1.  Command name and code

    NAOCRD     10   (Negotiate About Output Carriage-Return Disposition)

2.  Command meanings

        In the following, we are discussing  a  simplex  connection,  as
    described in the NAOL and NAOP Telnet options.

    IAC DO NAOCRD        The data sender requests or agrees to negotiate
                         about    output    carriage-return    character
                         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
                         carriage-returns.

    IAC DON'T NAOCRD     The data  sender  refuses  to  negotiate  about
                         output  carriage-return  disposition  with  the
                         data receiver,  or  demands  a  return  to  the
                         unnegotiated default mode.

    IAC WILL NAOCRD      The  data  receiver  requests  or   agrees   to
                         negotiate    about    output    carriage-return
                         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
                         carriage-returns.

    IAC WON'T NAOCRD     The data receiver refuses  to  negotiate  about
                         output  carriage-return disposition, or demands
                         a return to the unnegotiated default mode.

    IAC SB NAOCRD DS <8-bit value> IAC SE
                         The  data  sender  specifies,  with  the  8-bit
                         value,     which     party     should    handle
                         carriage-returns  and  what  their  disposition
                         should be.  The code for DS is 1.

Telnet NAOCRD Option                                Page   2



    IAC SB NAOCRD DR <8-bit value> IAC SE        The    data    receiver
                         specifies,  with  the  8-bit value, which party
                         should handle carriage-returns and  what  their
                         disposition should be.  The code for DR is 0.



3.  Default


        DON'T NAOCRD/WON'T NAOCRD.    In   the   default   absence    of
    negotiations  concerning  which party, data sender or data receiver,
    is handling output carriage-returns, neither party  is  required  to
    handle   carriage-returns  and  neither  party  is  prohibited  from
    handling them; but it is appropriate if at least the  data  receiver
    handles carriage-returns, albeit primitively.


4.  Motivation for the Option

        Please refer to section 4 of the NAOL and  of  the  NAOP  Telnet
    option descriptions.


5.  Description of the Option

        The data sender and the data receiver use the 8-bit value  along
    with the NAOCRD SB commands as follows:

    8-bit value          Meaning

    0                    Command sender  suggests  that  he  alone  will
                         handle carriage-returns, for the connection. 

    1 to 250             Command sender suggests that  the  other  party
                         alone   should   handle  carriage-returns,  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   qualification,
                         below.) 

    251                  Not allowed, in order  to  be  compatible  with
                         related Telnet options.

    252                  Command sender suggests that  the  other  party
                         alone  handle  carriage-returns,  but  suggests
                         that they be discarded.

    253                  Not allowed, in order  to  be  compatible  with
                         related Telnet options. 

Telnet NAOCRD Option                                Page   3



    254                  Command sender suggests that  the  other  party
                         alone   should   handle   carriage-returns  but
                         suggests  waiting  for  a   character   to   be
                         transmitted  (on  the other simplex connection)
                         before sending more data.  (See  qualification,
                         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   carriage-returns  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
        carriage-returns, the data receiver must do it, and

        (2) if both  data  receiver  and  data  sender  want  to  handle
        carriage-returns, 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 NAOCRD 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.

        Note that carriage-return delays, controlled by the data sender,
    must  consist  of  NUL  characters  inserted  immediately  after the
    character in question.  This is necessary due to the assynchrony  of
    network  transmissions.   Due  to the Telnet end-of-line convention,
    with carriage-returns followed by a linefeed, any  NULs  that  would
    otherwise  be  placed after the carriage-return must be placed after
    the linefeed, regardless of any modifications that may  additionally
    be made to the line feed (see NAOLFD 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 NAOCRD or DON'T NAOCRD command.