RE: Gen-ART LC Review of draft-ietf-xcon-common-data-model-23

[Oscar Novo <[e-mail]>]

Hi Ben,

 More comments inline as [ON1]. :)

-----Original Message-----
From: Ben Campbell [mailto:[e-mail]]
Sent: 8. maaliskuuta 2011 23:14
To: Oscar Novo
Cc: [e-mail]; General Area Review Team; The IETF
Subject: Re: Gen-ART LC Review of draft-ietf-xcon-common-data-model-23

Hi, thanks for the quick response. More comments inline. I've deleted any sections on which I think we are in agreement.

On Mar 7, 2011, at 6:07 AM, Oscar Novo wrote:

> Hello Ben,
>
> Thanks for your comments. Answers to your comments inline.
>
> Oscar
>
>
> -----Original Message-----
> From: Ben Campbell [mailto:[e-mail]]
> Sent: 5. maaliskuuta 2011 0:46
> To: [e-mail]
> Cc: General Area Review Team; The IETF
> Subject: Gen-ART LC Review of draft-ietf-xcon-common-data-model-23
>
> I am the assigned Gen-ART reviewer for this draft. For background on Gen-ART, please see the FAQ at <http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.
>
> Please resolve these comments along with any other Last Call comments you may receive.
>
> Document: draft-ietf-xcon-common-data-model-23
> Reviewer: Ben Campbell
> Review Date: 2011-03-04
> IETF LC End Date: 2011-03-04
> IESG Telechat date: (if known)
>
> Summary: This draft is almost ready for publication as a proposed standard. I have a few minor comments that should be considered prior to publication.
>

[...]

> Minor issues:
>
> -- section 3.3.1: "XCON-URI can not be resolved to addresses and/or ports."
>
> Then why does it include a port in the ABNF?
>
> [ON] Note that URIs can not be resolved to addresses and then to ports. That's why we state it very clear in the document that this isn't the case. Besides that, an XCON-URI can be viewed as a key to access a specific conference object. So, having a direct mapping to a URL can be useful some times for some conferences.

I understand that it doesn't map to a port. But I don't understand why you would include a "port" construction in a URI that can't map to a port. Actually, to generalize, I don't understand why one would use "host" either, since that construction is designed to carry addressing material, either in the form of a DNS name or an IPv4 or v6 address.

What do you mean by "direct mapping to a URL?" Do you expect to contruct an XCON URI from, say, a SIP URI?

[ON1] Ben, I think the XCON-URI identifier is unclear to you. I recommend you to read section 3.3 of my document. A XCON-URI identifier is created by the conference system and maintains a relationship between all the conference object identifiers in the conference. Figure 2 of my document shows an example and, in that case, the XCON-URI is a host identifier: xcon:[e-mail]. A XCON-URI can be anything. However, I can remove the port if it's unclear.

>
>
> Also,  can "host" be an IP address? If so, does that change the
> comparison rules? (i.e. 192.168.0.1 vs 192.168.000.001, suppression of
> zeros in an IPv6 address, etc?)
>
> [ON]I'm not an URI expert. Ted Hardie was the person in charge to review and verify the URIs of the document. For your question I would recommend you to read  RFC3986 section 6.1.

3986 says "string comparison, perhaps augmented by reference to additional rules
   provided by URI scheme definitions."


My point is that if you are really using the host and port constructions, they need some of those additional rules.  Certainly, 2 host:port constructions that match character for character are equivilent--but there's a number of ways host:port can be equivalent when it _doesn't_ match character for character. And that's not even counting aliasing--I'm talking about strict syntactic equivalence.

Wouldn't it better to just use some sort of string contruction (perhaps "unreserved") that would allow you to put something in it that looks like host:port, but without the meaning usually associated with those?

Was this concern discussed in Ted's review? If so, do you have a pointer to it?

[ON1] From RFC3986 section 6.1: "comparison methods are designed to minimize false negatives while strictly avoiding false positives."
Ted's agreed on the text mention in the document. He's an URI expert.


>
>
> -- 4.6.2, 1st paragraph:
>
> Are two users with the same signaling protocol allowed to have different authn mechanisms?
>
> [ON] Answering that question is out of the scope of this document. The Conference Control Protocol and/or RFC5239 (for instance section 11.1) should answer this question.

My question is whether the data model allows it. Why wouldn't that be in scope?

[ON1] From section 4.6.2 of the document: " Since a variety of signaling protocols are possible, a variety of authentication mechanism - determined by every individual conference servers - may need to be mapped from the different protocols. The specific types of authentication mechanism are beyond the scope of this document."

I'm concerned that <user-admission-policy> is a child of <users>, not <user>, so it looks like all the <user> elements with the same <users> parent must share the same admission policy. Am I misreading that? If not, how would you render multiple policies in the same conference?

[ON1] You render multiple policies using the <allowed-users-list> and <deny-users-list> elements. The <user-admission-policy> only lets the organizer to choose the policy of the whole conference: closedAuthentication, openAuthentication...


>
> -- 4.6.3, 1st paragraph:
>
> What if the user is using a protocol that doesn't use URIs?
>
> [ON] This section talks about the SIP URI or the xcon-userid URI defined in Section 4.6.5. The xcon-userid contains a unique conference user identifier (XCON-USERID) within the scope of the conference. This URI will always exist within the scope of the conference.

It lists SIP URIs and XCON-USERID URIs as examples. Are you limited to those schemes? What if someone is using XMPP for their signaling protocol--are they excluded since XMPP does not use URIs?

[ON1] A XCON-USERID is a unique conference user identifier assigned by the conference system. It's explained in the section 4.6.5 of the document. If there is an XMPP signaling protocol, such XMPP identifier will be mapped to the XCON-USERID.

>
> -- 4.6.5.3: "The real information about the user is still stored in the data model."
>
> This could use some elaboration. Does this mean that clients subscribing to the event package will get the real data, but be expected to conceal it from the user? Or that the data is only stored internally by the focus and not sent to subscribers?
>
> [ON] The data model specifies a set of elements for different use cases in every conference system. That doesn't imply all the elements has to be defined in every conference, only those elements needed for every conference system. RFC5239 section 11.2 explains a bit about the privacy concept in a conference.

My question wasn't whether they are used for a particular conference. It's more about how the data is protected when it is used by a conference. In particular, the text says this affects the way the data is provided to other participants. _How_ it effects it needs more detail.

I think that you mean that the focus should not provide the data to participating clients. _Not_ that said clients can be expected to conceal it from their users. This should be explicit either here or in the security considerations.

If you think RFC 5239 explains this, then a reference to it would be in order. I think it helps a bit, but I think you could use some stronger and more explicit language here.

[ON1]  What about modifying the text from:

"This element only affects the way the user information is provided to the other participants. The real information about the user is still stored in the data model."

To:

"This element only affects the way the user information is provided to the other participants. The real user information is stored in the data model but is not provide to the other participants of the conference."

>
> "'semi-private' value specifies that this user is anonymous to all users with equal or lesser permissions (determined by local policy) in the conference."
>
> This also needs elaboration, even if the way permission systems work is out of scope.
>
> [ON] what information you think is missing in this sentence? Note that the WG agree on not defining the local policy (roles semantic, permissions...) in this document.

What do you mean, in abstract, by "equal or lesser" permissions? That implies some assumptions about how permissions work, even though they are explicitly out of scope. Equal or lesser to what? Why assume permissions are hierarchical in the first place? Is it simply that the information should only be provided to users who have permission to see it? (a much simpler statement with fewer assumptions about how permissions work)

[ON1] So, what I meant with the "equal or lesser" is something like: "a semi-private value implies a root role is anonymous to a user role". Since the WG decided not to include the different roles and policies in this document, we have to leave it as an abstract concept and every local policy will define it as they think its appropriate.

>
> --4.6.5.3:
>
> I'm having trouble imagining what a role of "none" might mean.
>
> [ON]A role of "none" indicates that any role is assigned; It was a WG resolution:
>
>       http://www.ietf.org/mail-archive/web/xcon/current/msg02102.html

A comment to that effect in the text would be helpful.

[ON1] I can add it to the document.

>
>
> -- 8, general:
>
> It seems like some comments on protecting anonymity of anonymous users would be worth a mention here.
>
> [ON] The data model is part of the RFC5239 and this RFC is already handling quite well anonymity. We rather want to repeat information in the data model.

See my previous comment above. I think you need more _somewhere_.  At least, some explicit references to specific passages in 5239 that are relevant to anonymity.

I push on this, because anonymity is an area often gotten wrong by implementors and protocol designers. It warrants careful attention.

[ON1] I can add the RFC5239, section 11.2 reference in this part of the text.

>
> -- 8, paragraph 6: "The confidentiality of the database SHOULD be unauthorized users, given that the data model sensitive elements (e.g., passwords)."
>
> Confidentiality of a database containing passwords only rates a SHOULD?
>
> [ON] It might be the case in some particular scenarios where the confidentiality can be ignored. For this reason, we decided not to impose confidentiality (using SHOULD instead of MUST) in the document and to leave that decision to the administrator of the conference.

Really? Can you give an example where it's safe to ignore confidentiality of _passwords_?

[ON1] There are conference which don't define any password and any sensitive information. Providing confidentiality at a conference may seem strange or counterproductive sometimes, especially these days where event sessions are routinely streamed and videoed for anyone who wants to watch.

>
> "Administrators of conferencing systems SHOULD also avoid disclosing information to unauthorized parties when a conference is being cloned or when a sidebar is being created."
>
> This could use elaboration. Why is creating a sidebar more dangerous than other operations not mentioned here?
>
> [ON] Sidebars manipulation are described in RFC5239, section 9.4

If you think that answers the question, then a reference would be in order. But on a quick scan, I don't see where that section explicitly discusses security risks in creating sidebars.

[ON1] For instance, RFC5239, section 9.4.2 is talking about the external sidebars. In those sidebars, users -which are external to the conference - are *joining* the conference. Disclosing information to those unauthorized users is essential. That's just an example.
The data model describes the data of the conference objects which are described in RFC5239. So, the data model is *complementing* RFC5239. The aim of the data model is not to repeat the information already written in RFC5239 rather than defining the missing information.

>
> Nits/editorial comments:
>
> -- general:  Please put vertical white space between bullet list entries. Otherwise, the resulting walls of text become very hard to track visually.
>
> [ON] vertical whitespace? What do you mean? I'm already using spaces between every bullet and the text. Do you mean to leave spaces between the bullets?

You have _horizontal_ white space between a bullet and the text within a particular list entry. You do not have _vertical_ white space (i.e. blank lines) between entries.

See http://www.rfc-editor.org/rfc-style-guide/rfc-style section 3.1.

[ON1] got it. I can add vertical white spaces between bullets.

>
> -- Section 1:
>
> It might be nice to have a paragraph defining what you mean by "conference" before jumping into conference attributes.
>
> [ON] The definition of conference is already defined in RFC5239 section 4.

Sure, but it would be reader friendly to have a sentence describing it here. I'm not talking about a detailed description.

[...]

[ON1] The terminology part of the document states:

"This document uses the terminology defined in the Centralized
   Conferencing Framework [RFC5239], the SIPPING conferencing framework
   [RFC4353] and the BFCP (Binary Floor Control Protocol) specification
   [RFC4582].  Readers of this document should be familiar with the
   terminology used in those documents."


>
> -- section 3.3, first paragraph after the diagram:
>
> is XCON-URI intended to be an acronym? If so, you describe it as a "unique conference object identifier", but never actually expand the acronym itself.
>
> [ON] XCON-URI is not an acronym
>

Hmm. It doesn't  stand for "Centralized Conferencing - Universal Resource Identifier"?

[...]

[ON1] XCON-URI is a conference object Identifier.

>
> -- 4.2.13, 6th bullet:  "It is expected..."
>
> Who expects it?
>
> [ON] Shall I rephrase it to:
>
> [ON]"It is expected that these controls are sufficient for the majority of the basic conferences."

Still, "It is expected" by whom?

Maybe just say "These controls are sufficient for the majority of basic conferences."?

[...]

[ON1] Right, I'll add it to the document.

>
> -- 4.6.2, last paragraph: "In all other cases, the appearance of an <allowed-users-list> and <deny-users-list> MUST be ignored."
>
> What other cases? I assume you don't mean to say that any extensions are prohibited from using allowed-user-list or deny-user-list--but one can read it to mean that.
>
> [ON] That paragraph was an AD review proposal:
>
>       http://www.ietf.org/mail-archive/web/xcon/current/msg02495.html

With all due respect to Robert, I think the current text is unclear. I interpret "All other cases" to mean "All cases except for those enumerated above". That is, all cases other than the one it's talked about so far.  The text goes on to say some things about future extensions--which seems to contradict the first sentence. I think you mean to say that, except in the case where a future specification gives guidance otherwise, all other cases MUST be ignored.

One simple fix would be to move the first sentence to the end of the paragraph. Something to the effect of:

"Future specifications using the <allowed-users-list> and <deny-users-list>  lists must provide clear guidance... .  In all other cases, the appearance of an <allowed-users-list> and <deny-users-list> MUST be ignored."

Another approach would be to say "All other cases... MUST be ignored, except as stated otherwise in a future specification describing..."

[...]

[ON1] I recommend you to talk with Robert about your proposed change. If he accepts this change I'll modify my document. Otherwise, I will stick to the AD proposal.