TN3270 AYT

[Michael Wojcik]

[Apologies for the cross-post; it seemed possible that some of the
TN3270 experts might hang out on c.p.ibm. Followups set to
c.p.tcp-ip.]

I'm fine-tuning my TN3270 / TN3270E server implementation, and I
can't seem to find anything concrete about how to handle the Telnet
Are You There (AYT) command flow. In NVT mode, AYT processing is
pretty clearly specified in RFC 854: when the server receives IAC
AYT, it should respond "with some visible (e.g., printable) evidence
that the system is still up and running" (page 7), or later "Send
back to the NVT some visible (i.e., printable) evidence that the AYT
was recevied" (12). (The switch from "e.g." to "i.e." is intriguing;
is one a typo?)

However, this doesn't make much sense for TN3270 in 3270 mode, with
the Binary and EOR options in effect. My server is in effect an
SSCP, not a PLU; I shouldn't really be tampering with the screen at
all (unless this is a TN3270E session in SYSREQ mode). And it's
not trivial to inject some "visible evidence" without interfering
with the running application's display.

At the moment, I reply to AYT with a Telnet no-op (IAC NOP), which
seems safe. (I ensure that it comes between Telnet records, not in
the middle of one, as RFC 2355 recommends.) Does that sound like
an appropriate response? It doesn't give the user anything, but it
at least confirms to the client that the connection is up.

Any other suggestions, or ideas about how AYT is normally handled
by TN3270 servers? Is it just ignored?

--
Michael Wojcik michael...@microfocus.com

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