How do you feel about adding the following (first sentence) to your section 4.2 proposal?
Note: The IPP Everywhere required "_print._sub._ipp._tcp" and "_print._sub._ipps._tcp" advertisements, which are used to distinguish between legacy IPP and IPP Everywhere support, should not be confused with "_printer._tcp" and "_printer._sub._http._tcp" advertisements referenced in [BONJOUR]. The first version of the Bonjour Printing Specification was published by Apple shortly after the Internet Printing Protocol was published by the IETF. As the Line Printer Daemon Protocol [RFC1179] was considered the most popular network printing protocol at the time, the "_printer._tcp" DNS-SD service type (LPD) was assigned as the "flagship" protocol for DNS-SD advertisements. Similarly, the HTTP service registration for the embedded web server uses the "_printer._sub._http._tcp" service type, even for IPP Printers.
Thanks,
Chris
Christopher Rizzo
Xerox Corporation
GDG/Discovery/Advance Technology
26600 SW Parkway Ave.
Wilsonville, OR 97070-9251
Phone: (585) 314-6936
Email: Christopher.Rizzo at xerox.com
"The realization came over me with full force that a good part of the remainder of my life was going to be spent in finding errors in my own programs."
-Maurice Wilkes, Memoirs of a Computer Pioneer
From: Michael Sweet <msweet at msweet.org>
Date: Monday, March 2, 2020 at 12:51 PM
To: Christopher Rizzo <Christopher.Rizzo at xerox.com>
Cc: PWG Workgroup <ipp at pwg.org>
Subject: Re: [IPP] PWG Call for Objections: IPP Transaction-Based Printing Extensions v1.1 (TRANS) (ends March 27, 2020)
Chris,
On Mar 2, 2020, at 2:52 PM, Rizzo, Christopher <Christopher.Rizzo at xerox.com<mailto:Christopher.Rizzo at xerox.com>> wrote:
Thanks Mike,
Yes, I noticed the IPP Everywhere requirement after sending out the note.
So why do we need to distinguish between IPP and IPP Everywhere printers?
Because IPP printers have very limited requirements WRT file format support, attribute support, and so forth. Until AirPrint and IPP Everywhere, IPP was treated as just another protocol to send printer-specific data through, and even those printers that supported a generic PDL like PDF didn't necessarily support things like copies, media, and so forth.
And if this is needed, is this the primary way to distinguish between them, or are there other indications? For example, is there an IPP Everywhere version TXT record (or should there be)?
You may be able to "guess" based on the list of formats in the TXT record's "pdl" key, and once you connect to the printer you can do a Get-Printer-Attributes to confirm your guess.
But browsing for _print._sub._ipp._tcp and _print._sub._ipps._tcp services (printers) is guaranteed to work...
And why use "_print" in IPP everywhere when Bonjour spec uses "_printer".
The Bonjour Printing spec was written long before IPP, IPP Everywhere, or AirPrint were ubiquitous, so the focus was on being a) discoverable and b) supportable by all network printers regardless of protocol. LPD is the "flagship" protocol (ha!) and thus all printers have to register their service name for the "_printer._tcp" type (LPD), even if the port number is 0 (meaning "I don't really support this protocol").
Since _printer._tcp is the flagship protocol, the sub-type for the printer's web page is "_printer._sub._http._tcp".
It all seems to just add confusion. Maybe IPP Everywhere spec should include information clearing up this confusion (ie - a note that says "_print" IPP Everywhere service advertisement should not be confused with "_printer" from Bonjour spec, and that the "_print" advertisement is different (required in addition to) from the standard Bonjour advertisement to specifically differentiate an IPP Everywhere supported printer).
Apologies for my confusion, but when you have to read several specs (RFC, AirPrint, Bonjour Printing spec, IPP Everywhere) and try to coalesce all the requirements, it gets a little confusing.
I want to avoid making things more confusing, and also don't want to restate every requirement from the Bonjour Printing specification...
How about I add the following note at the end of section 4.2:
Note: The first version of the Bonjour Printing Specification was published by Apple shortly after the Internet Printing Protocol was published by the IETF. As the Line Printer Daemon Protocol [RFC1179] was considered the most popular network printing protocol at the time, the "_printer._tcp" DNS-SD service type (LPD) was assigned as the "flagship" protocol for DNS-SD advertisements. Similarly, the HTTP service registration for the embedded web server uses the "_printer._sub._http._tcp" service type, even for IPP Printers.
________________________
Michael Sweet
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