Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!pasteur!ucbvax!UOTTAWA.BITNET!SIMXT
From: SIMXT@UOTTAWA.BITNET (Lew Shepherdson)
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re: Printing with TN3270
Message-ID: <8804050050.aa01422@Louie.UDEL.EDU>
Date: 5 Apr 88 04:26:32 GMT
References: <jbvb@vax.ftp.com>
Sender: usenet@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 34

Printing is done on 328x printers in one of two ways:
  1) Either a 'local copy' operation initiated by the COPY key.  This is
     handled by the 3x74 controller without any interaction with the host.
  2) By a host application writing directly to the printer.  This is the
     more interesting case, and is used extensively by a number of host
     applications, such as CICS and IMS.  Typically the way this works
     is that the host issues a VTAM request to 'acquire' the printer
     (contrast to a 3278 terminal which typically 'logs onto' the host
     application and the application 'accepts' the logon).  If the printer
     is available, a session is then established between the application
     and the printer, and printer data streams can be sent to it.
     (Implementors note that there are two kinds of 328x printers...LU1
     and LU3...do LU1 first, everything supports it.)

     All a TN3270 implementation has to do is distinguish printer sessions
     from terminal sessions, and then handle the printer data streams
     (either LU1 SCS (SNA Character Set) or LU3 DSP (mumble mumble)).

     The tricky part is on the host.  On VM, the Logical Device Facility
     now supports printers.  The TELNET server would have to create a
     logical printer and then 'ATTACH' it to the correct application
     (however that is determined).  On VTAM implementations, the TELNET
     server has to 'open' an LU with the right printer name, and wait for
     it to be acquired by an application.  In both cases, there has to
     be some way to associate the TN3270 printer with the 'correct' host
     printer.  There are also problems with knowing when the printing
     is finished, and when to release the 'virtual' printer.

     So, the good news is that it can be done (we did it for a non-TN3270
     implementation)...the bad news is that it requires a lot of host
     kludges and tradeoffs (choose carefully to match the application
     and how the users want to use the printers).

Lew Shepherdson
Simware Inc.  (SIMXT@UOttawa.Bitnet)