Subject: [Simple] Pres Data Model Open Issue #3, UUID URN or something else

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 28 Sep 2004 17:19:11 -0400

One of the things the design team spent a lot of time discussing was 
what a device ID looked like. Our conclusion, as documented in the I-D, 
is that its a URN. We can't lock down the specific type of URN, but for 
things where MAC address is a useful unique device identifier, the UUID 
URN (as it makes use of a MAC address) is a good choice.

However, upon a more detailed read of the UUID URN specification, I am 
not sure we can use it. The reason is that the UUID URN spec 
(http://www.ietf.org/internet-drafts/draft-mealling-uuid-urn-03.txt) 
describes several ways of computing the URN. There are actually four 
versions. The time-based version uses the host MAC, along with the 
current time, to generate the UUID. The name-based version doesnt use 
time, but relies on a unique namespace, such as DNS or URIs, as a seed. 
MAC address is not a choice.

So, the problem is, the UUID form that utilizes the MAC address also 
includes a time-based component. This serves to provide uniqueness, but 
makes it useless as a meaningful identifier that other presence sources 
- like an ethernet switch or 802.11 AP, would be able to provide 
information about.

So, the options as I see them are:

1. use UUID URN anyway, lose the correlation properties we wanted
2. dont specify the URN form at all
3. don't specify the URN form in this document, but work on this problem 
in downstream specifications

I would propose approach (3). In particular, I think the data model 
should revert to being agnostic on the URN scheme, reference the UUID 
URN as one possibility, document its problems. We should develop a 
separate specification that defines guidelines for choosing the URN for 
various devices in order to get the correlation properties we want. I 
also think we should take a stab at defining a few URN schemes that 
would be useful - MAC and ESN in particular.

Comments?

Thanks,
Jonathan R.
-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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From: Paul Kyzivat <[email-masked]>
Date: Tue, 28 Sep 2004 18:19:16 -0400

> would be useful - MAC and ESN in particular.

I think it does make sense to leave the particular choice out of this 
document.

I do think the problem with UUID can be dealt with in a couple of ways:

- for some kinds of "devices", like softphones and IM clients, it is
   probably fine as-is. They can typically have multiple instances per
   device, so they must construct and instance id and save it
   persistently as part of the instance configuration.

- for a dedicated device, like a phone, that can't or doesn't want to
   use the above technique, a cannonical mac-based uuid can be
   constructed by using a fixed time (e.g. zero) along with the mac.

	Paul

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From: Henning Schulzrinne <[email-masked]>
Date: Wed, 29 Sep 2004 14:35:30 -0400

As discussed previously, a device may not even have a MAC or may have 
several (if it is a composite or a multi-homed device). Thus, this seems 
inherently difficult. We went through this whole discussion before, I 
believe.