Re: Difference between ipp, ipps, http, https CUPS protocols?

[Dan Purgert <dan@djph.net>]

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Kent West wrote:
> After some testing, I find that selecting "http" creates a working 
> printer; selecting "ipps" does not. The latter generates an error page 
> that says:
>
> Unable to open PPD file:
>
>     Missing asterisk in column 1
>
>
> So apparently there is some difference between these protocols, and I'm 
> left wondering what the differences are, and which one I should select.
>

Most likely, the spooler chokes because you don't have a valid SSL
certificate on the printer (or the print-server). Therefore, neither
"IPPS" nor "HTTPS" would work.

Again, the "choice" of protocol comes down to "what does your printer
support" (most everything newish should support IPP). 

Without getting into way too much detail (and needing to google to
refresh my memory), IPP is basically an "enhanced" LPR/LPD, that instead
of you needing to write all the control software "client side" (i.e. the
machine sending the print job having the options in an rc file, on top
of one or more page filters), an extra communications / settings channel
is opened between the printer and machine trying to print, so they can
communicate about capabilities, and change them on the fly (e.g. want
this job to one-off print single-sided? Just tell the printer), rather
than having to edit a config file (and possibly restart services on the
machine printing).

I believe the newest printers offer a way to print "driverless" via IPP
as well -- that is, rather than needing a device-specific PPD, the use
of IPP lets you just send a standardized "printing format" (PDF, PCL,
something like that), and that "printing format" plus the options you
told it via the control channel gets you a nice document.  Though, that
might just be vaporware at the moment.

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