Installing tn3270


Bob Braden (braden@venera.isi.edu)
Wed, 9 Jul 86 11:26:15 PDT


I have recently installed the Berkeley version of tn3270 on my Sun 3 work
station. I used the public tar file tn3270tar, mentioned in Greg Minshall's
message copied to tcp-ip on June 6; the main program file is dated 5/13/86.

The Sun environment caused some difficulties; for example, you must give
tn3270 a Sun window of exactly the size of the emulated 3278 screen (in
my case, 43*80; see below), or it just dies due to bad return code form
curses. It also took me awhile to work out a sensible mapping of the
essential 3278 keys onto the Sun 3 keyboard, avoiding the keys that Suntools
wants to keep to itself.

In addition, there were some significant problems in tn3270 itself, when used
to access both the Wisconsin VM code and the UCLA MVS code. These were as
follows:

1. It has been recommended that the terminal type be updated to a 3278-2,
   which has 24 lines of 80 characters. However, both VM and MVS are prepared
   to handle the more modern screen size of 43*80, so if you have a competant
   terminal (like a Sun), I strongly suggest you use the terminal type 3278-4.
   In this case, it is necessary to update the defined constant NUMBERLINES
   in 3270.h to be 43.

   [tn3270 really should take the terminal type (or at least a Boolean
   selecting long/short screens) from a parameter, and NUMBERLINES should
   be a variable set as a result.]

2. tn3270 does not support the Erase Write Alternate command, which both
   VM and MVS send. Its effect should be exactly like Erase Write, but it
   needs to be included in the case statement in datastream.c, or it defaults
   to Write; the result is a failure to clear the screen sometimes, which is
   BAD.

3. tn3270 supports only the non-SNA commands, not the SNA commands.

   Here's a summary of the relevant command codes:

   command non-SNA SNA
   ------------------------------------------
   Erase/Write x'05' x'f5'

   Erase/Write
      alternate x'0d' x'7e'

   Write x'01' x'f1'

   Erase All
      unprotected x'0f' x'6f'

   Read Buffer x'02' x'f2'

   Read Modified x'06' x'f6'

   It happens that VM and MVS use the non-SNA and SNA commands, respectively,
   as most appropriate to their system environment. I believe that IBM FSD
   intends to standardize on the SNA flavor, and update the VM code to
   send it. In any case, any reasonable 3278 emulator should accept both
   sets (I think the VM and MVS User Telnets do so).

4. tn3270 does not properly return to NVT mode when the server negotiates
   back to NVT mode (although the VM code doesn't do this, the MVS code
   does).

5. tn3270, when in NVT mode, carries over the egregious bug from the
   Berkeley telnet program: in local echo, it send end-of-line as
   LF instead of the CR LF dictated by the TELNET protocol spec. Why
   do we have to put up with this petty protocol anarchism?

Of these problems, 1-3 are the most serious and fortunately are quite
trivial to fix. Upon request, I will send the updates I used.

________
Bob Braden



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