Subject: TN3270E Byte-Doubling & Flush Functions

From: "Marty Williams" <[email-masked]>
Date: Thu, 13 Nov 1997 11:05:40 -0600

Please find attached draft proposals for eliminating byte-doubling and
adding a "Flush" function for TN3270E.  Your comments, suggestions, etc are
greatly appreciated.

Thanks,

Marty Williams
[email-masked]
OpenConnect Systems

---

From: "Derek W. Bolton" <[email-masked]>
Date: Fri, 14 Nov 1997 10:14:03 +1100 (EST)

Hi Marty,

I'm not across the political issues the might be involved,
but I was hoping that byte-non-doubling could be negotiated
at the telnet layer rather than as a tn3270e suboption.
That would bring many benefits:

- It could be adopted by other telnet-based protocols.
  Ideally, it would be transparent to the higher layers.

- It would avoid mangling the layers.

  At present, the byte double/undouble is logically at a layer
  below the tn3270/tn3270e layer.  Your proposal changes that in two
  ways.  First, the higher layer can turn the function off.  That's
  not too bad, but the nasty part is that the lower layer then
  has to understand part of the tn3270e header and dynamically
  turn the function back on.

- By implementing a more generic mechanism - not tied to tn3270e
  headers - a server that forwards partial chains could still
  avoid ff-doubling.

Here's the sort of thing I'd prefer.  This is off-the-cuff, so
there are probably some holes in this, but it conveys the
flavor:

- Negotiate new telnet option to permit length-and-data transmissions.

- New telnet commands switch into and out of length-and-data mode.
  The switch applies to the datastream being sent in the same
  direction.  It has no effect on the reverse datastream.

- While in length-and-data mode, the datastream consists of
  logical packets.  Each packet is either:

  - A telnet command (introduced by 0xFF), or
  - A 2-byte length field (max 0xFEFF) followed by that many bytes
    of uninterpreted data.

  (Actually, could allow up to 0xFF7F for the length since all
  telnet commands are beyond that.)

What do you think?

Regards,
  Derek

> Please find attached draft proposals for eliminating byte-doubling
> and adding a "Flush" function for TN3270E.  Your comments,
> suggestions, etc are greatly appreciated.