moore@PULSAR.FAC.CS.CMU.EDU (Dale Moore) (02/25/89)
Should there be a standard protocol for talking to printers? Should Adobe define a standard, and encourage PostScript printer manufacturers to follow the standard? In the early days of PostScript, there was one connection to the printer. It was RS232 (or RS422) or possibly Appletalk. All the other PostScript vendors who wanted to play the game supported one or both of these low level protocols. On top of these low level protocols, Control-S and Control-Q were used for flow control. Today, many PostScript printer manufacturers are connecting their printers to fast local area networks, such as Ethernet. Each manufacturer is implementing its own protocol(s) on top of the LAN for functions such as flow control, job queueing management, file I/O, font downloading and the other functions associated with the printer. I have heard of four Ethernet printer protocols, two from Digital Equipment, one from Talaris, and one from QMS, with possibly more coming in the future. I'll go over what little I know of them here; I'm sure that some of you can fill in the missing pieces. Digital Equipment Corporation has two printing protocols: LAPS and Print Server. LAPS is Local Area Print Server System (?) and is run on top of DECnet over Ethernet. This protocol is, I believe, proprietary. DEC's other protocol, Print Server Protocol, is IP/TCP based. DEC is promoting it as a standard. It is quite reasonable for PostScript printers, but I think that it leaves little room for printers that have additional printing standards (LN03, LaserJet, Tek 4014 for example). Talaris's protocol is T-LAP (Talaris Local Area Printing). It is also an Ethernet protocol. They currently use an Ethernet data link layer protocol, but they have plans on implementing it on top of IP/UDP. I also believe that it is a proprietary protocol, but I could be wrong. I know nothing about the QMS protocols, except that they work over Ethernet. It can be sometimes quite expensive getting support for a machine/printer combination. For example, for several years, DEC did not support a non-DECnet Ethernet protocol. Many of our Unix boxes could not directly exchange files with our large DEC PostScript printers, because our Unix machines could not speak DECnet. Another example, Talaris provides the software so that VMS can communicate with their new printer over the Ethernet. But one sales rep I talked to said that they could not provide the software for any version of Unix at this time, but they hoped to do so in the future (no time given). Should we ask manufacturers to develop and standardize a set of protocols? Or should we let the market shake itself out? Deciding the latter runs the risk of ending up with a large set of printers that no one wants to...or *can*...talk to. Just as PostScript was adopted as a standard, should Adobe adopt and promote a set of printing standards? Or should it be up to the printer manufacturers? Do we consumers really have a say, short of voting with our pocket-books? Or should we wait for the ISO OSI protocols, which have always been only three years away? Dale Moore Research Systems Programmer School of Computer Science Carnegie Mellon University Pittsburgh PA 15213 USA --
ttl@astroatc.UUCP (Tony Laundrie) (03/01/89)
I'm not sure how related this question is, but here goes: Our laser printer is connected to a VAX running UNIX. We send things to the printer with lpr. Some PostScript programs can be made to write files back to the RS232 link. How can I read them? Does anybody have a modified version of lpd that puts files from a laser printer into some temporary file? From looking at /usr/src/usr.lib/lpr/printjob.c on our system, it seems that our lpd only reads 1-word responses. Thanks. ...uwvax!astroatc!ttl