Re: Telnet binary mode


Mark Crispin (MRC%PANDA@SUMEX-AIM.ARPA)
Sun 24 Aug 86 06:03:52-PDT


Joe -

     A purist would argue that NVT ASCII is 7 bits unless binary mode has
been negotiated. The Telnet specification is vague on this point, but it
does refer to the "128 possible characters in NVT ASCII" in a few places.
I believe that 8 bit transmission in non-binary mode is a bug, since it
interferes with local parity handling.

     The parity issue is important, although many implementors (myself
included, alas) have never bothered to implement parity correctly.

     I know that vanilla DEC TOPS-20 does not enforce 7-bit NVT ASCII on
input to an NVT. It also doesn't enforce IAC doublings on output from an
NVT. I consider both of these to be bugs, in spite of the fact that
certain individuals have written programs to exploit them. The PANDA
versions of TOPS-20 (SIMTEL20, STL-HOST1, DREA-XX) all have these bugs
fixed, as do several other sites.

     Significantly, the TAC also enforces 7-bit ASCII in non-binary mode.

     I think that it is prudent to negotiate binary mode on any Telnet
connection in which you wish to transmit 8-bit ASCII. The only hosts I
know of which have problems with binary mode are certain broken versions
of Unix. As far as I can tell mainstream Unix handles binary mode
reasonably.

-- Mark --
-------



This archive was generated by hypermail 2.0b3 on Thu Mar 09 2000 - 14:36:35 GMT