Now is the time to think about using collections or stuctures - we should bite
the bullet and just do it. This is a clear example of where it is needed.
Creating structured strings is out of character with the remaoinder of the IPP
protoocl (I.e. no string parsing).
In this case a 'supported-connections' (or whatever you want to call it) would
.. note that this is not a proposal for an exact scheme for URI rather a cal to
address the current weakness in the core encoding
"McDonald, Ira" <imcdonald at sharplabs.com> on 03/01/2000 01:15:44 PM
To: "'Hugo Parra'" <HPARRA at novell.com>, ipp at pwg.org, srvloc at srvloc.org
cc: (bcc: Paul Moore/AUCO/US)
Subject: RE: IPP> [URGENT] RE: Help - Naming problems in SLP 'service:prin ter'
[URGENT - decision needed within 3 days]
You make good points below. Tom Hastings and I have been
noticing the same problem ('lockstep' nature of the three
underlying IPP attributes) in the Set-Printer-Attributes
new proposed IPP operation (e.g, what if you only set one
of the three and now they have an unequal number of member
values - oof!).
Since changing the names of most of the attributes in the
SLP 'service:printer:' to prefix them with 'printer-' (to
allow clean translation to LDAP and other flat namespace
directory protocols) is NOT a backward compatible change,
the next template version will have to be 'v2.0' anyway.
So, I hereby propose a new base syntax in IPP and a slight
revision of your example below. Remember that since commas
are legal in the body of URI, we still need to use the '>'
delimiter in SLP to separate a list of URI. And since ';'
is legal in the body of URI, we ALSO need to use some
special character to separate parts (see example below).
I propose to use '<' (these characters are 'safe' because
they are 'delimiters' in RFC 2396, i.e., they stop URI
A new base syntax in IPP called 'xri' (Extended Resource ID),
as in the following example (lines folded for email length):
uri=ipp://abc.com/p1< sec=tls;ssl3< auth=basic< >
uri=lpr://abc.com/pq< sec=none< auth=none< >
Note that I downcased your keywords (URI, SEC, AUTH) to make
them standard IPP keywords. There are two Extended Resource
IDs listed in the above SLP template attribute example. In
IPP, which explicitly supports multivalued attributes in the
encoding (without comma or other delimiter), the first XRI
(ipp:) would be value one and the second XRI (lpr:) would be
value two (and they would not contain '>').
We can't undo all the IPP products that already shipped with
these three parallel ordered attributes, but we *can* decide
they were a mistake and disambiguate them by *adding* the new
synthesis attribute 'printer-xri-supported' and making the
old separate attributes 'read-only' for 'Set-Printer-Attributes'
We need to make this decision ALMOST IMMEDIATELY, so that
I can get a new I-D out for 'service:printer:' before next
Friday (10 March)
- Ira McDonald (consulting architect at Sharp Labs America)
From: Hugo Parra [mailto:HPARRA at novell.com]
Sent: Wednesday, March 01, 2000 10:12 AM
To: ipp at pwg.org; srvloc at srvloc.org
Subject: IPP> RE: Help - Naming problems in SLP 'service:printer'
I realize this is the eleventh hour (if not a little later) to bring this up
again, but I think it's important.
I'm convinced IPP made a serious mistake in defining the
"printer-uri-supported", "uri-authentication-supported" and
uri-security-supported" as parallel attributes. We've already gotten a
glimpse of the challenge it will be to keep them in sync under all
One of the arguments for their current definition was that it would
facilitate extensions. We reasoned that if a new dimension were ever needed
(a good assumption by the way, v1.1 already added
"uri-authentication-supported" and "uri-compression-supported" has been
discussed), all we would have to do is add another parallel attribute to the
set. In actuality, this illustrates how broken the model is. It negates
interoperability between systems that support even slightly different
parallel sets. An additional, though less serious, problem is that it can
cause an unwieldy number of permutations as more
security/authentication/etc. combination become possible.
Now we're going to compound the problem by defining an SLP template and LDAP
*abstract* scheme for printers that has the same horrendous problem! I
propose that we use a different model, one that does away with parallel
attributes. If it's too late to fix IPP (and I'm not really sure it is), at
least let's fix the SLP and LDAP representation.
I'd like to propose defining a multi-valued attribute of syntax STRING by
the name "printer-uri-supported-information" (or something like it) that
replaces "printer-uri-supported", "uri-authentication-supported" and
"uri-security-supported". Each value for this attribute must be populated
"URI=ipp://abc.com/p1; SEC=tls,ssl; AUTH=basic;"
Multiple values for a section should be allowed as long as they're valid
with all other combinations possible from the other sections included in the
same string. If they're not, then a new value should be created. Consumers
of this attribute are required to ignore section KEYs they don't recognize
and assume <no-value> for KEYs that don't appear.
This representation enables very powerful extensibility and gets out of the
business of updating the IPP model, SLP template, and LDAP schema every time
a change is needed.
>>> "McDonald, Ira" <imcdonald at sharplabs.com> 02/29/00 02:38PM >>>
Thanks very much for clear direction. I'll make a serious effort
to get the revised SLP 'service:printer' schema out before the
I-D cutoff on 10 March (for the Adelaide IETF plenary).
I labelled the last one 'v1.0' in the template source. Should
I label the revision 'v1.1' in the template source? Or should we
try to just publish the fixup as 'v1.0'?
- Ira McDonald (consulting architect at Sharp Labs America)
(co-editor of SLP 'service:printer' template)
High North Inc
From: Erik Guttman [mailto:Erik.Guttman at germany.sun.com]
Sent: Tuesday, February 29, 2000 2:26 AM
To: McDonald, Ira
Cc: 'Erik.Guttman at germany.sun.com'; 'srvloc at srvloc.org'; 'ipp at pwg.org'
Subject: Re: Help - Naming problems in SLP 'service:printer'
>> Many of the SLP 'service:printer' attributes (largely taken from the
> IPP Model) lack a proper scope prefix 'printer-'. This forces us to add
> those prefixes when translating to an LDAP schema.
>> Tom Hastings (editor of IPP Model) just asked me to write to you and ask
> if we can (once more) update the SLP 'service:printer' template and add
> the proper 'printer-' prefixes, to make the translation cleaner and any
> blind mapping (by an SLP-DA to an LDAP directory server) safe. Some of
> the numerous currently 'unsafe' attribute names include:
>> Has IANA already registered <draft-ietf-svrloc-printer-scheme-05.txt>?
still lacks the registrations. I sent them to IANA in December!
> If I turn out a revised I-D within the next 10 days, can we send that to
> IANA instead?
Even if the template version 1.0 goes into the repository, we can submit
the new draft as template version 1.1. No problem.
I intend to talk to some members of the IESG soon about how to escalate
interaction with IANA so the template registry will get started.
> Tom Hastings and I are very concerned about polluting the LDAP flat
> attribute namespace with names like 'uri-security-supported' and
> 'media-supported' without proper 'printer-' prefixes.