1. RPIDS and tuple issues Henning Schulzrinne with help from Paul Kyzivat
SIMPLE WG (Interim Meeting, May 2003)

2. Open Issues From IETF56 SIMPLE minutes: Mailing list discussion
RPIDS as successor to PIDF?
tuple semantics
labeling elements: uniqueness across time, space, …
Mailing list discussion

3. Step back: what do we want presence to support?
General notion of reachability for communications
Generally, device-mediated
Also, direct human-human communication (drop in and chat)
Later, maybe status (“X is travelling, so no point in waiting for her to start the meeting”)

4. How does the system work?
RPIDS document (?) should spell out at least one scenario
presence notification
u1: p1,p2|p3
u2: p1,p4
u3:p5,p6
p1  u1 or u2
p1+p2  u1
p5, p5  u3
INVITE u1
Want: p1,p2,p9
caller
callee

5. Open issues – what is a tuple?
Three models have been proposed:
All share same AOR (e.g., selection via CP
availability of caller preferences
Custom-generated address for each capability set (maybe several for each device); e.g.,
longevity of address?
tight relationship with proxy server
Contact addresses representing devices; e.g., tel: ,
privacy
how long is address valid? (watcher  address book)
Not necessarily mutually exclusive – need all of them

6. Tuple semantics Tuple represents opaque entity, e.g., a group
easy, since few characteristics except “this is a group”
intersection or union probably makes little sense
Tuple represents media capability
“reachable by audio”
may be implemented by multiple devices
Tuple represents device (or location)
may become more important as location information increases
can be represented either by host or user part:
direct contact
unique label

7. Tuple semantics audio video text home office mobile
yes no
office
yes, but low quality
mobile
can, but inappropriate now
can’t
preferred
But really N-dimensional hypercube:
arrange by ‘category’, ‘placetype’, ‘privacy’, …
Thus, can’t hope to represent as anything but enumeration
While number of descriptors is large and will grow, number of instances represented is likely to remain smallish (~3-5?)
mobile multi-function devices make smaller number of devices seem likely

8. Tuple perspectives
hide details of user devices (and maybe location or other aspects)
sometimes, address could be used to guess user location or behavior (aol.com  home, mobile device  traveling)
not all users will have the ability to create injective (1-1) identities
want centralized policy enforcement point for simplicity
focus on callee control
provide details
description insufficient for informed caller choice
emphasis on caller empowerment

9. Anonymous tuples Tuples without contact
Current meaning: face-to-face communications
Needed since presentity URI may not be usable by communications application (e.g., pres:)
May also become useful for presence focused on activity
e.g., track where rescue worker (soldier, nurse, Maytag repairman, …) is and environmental characteristics (heart rate, air temperature, …)

10. Tuple – resolution? Hard to anticipate uses UI considered solvable:
 document choices and trade-offs
UI considered solvable:
represent as enumeration or table (matrix) with properties in either case
use <note> to provide hints
Can’t rely on caller preferences for the near future
should we require support on caller side for disambiguation? (Opinion: policy issue)

11. Open issues - label PIDF defines "id" tuple tag
allows to replace changed tuples without sending all the unchanged ones
not clear from spec who modifies (PA?) and what its lifetime is
Separate "label" tag proposed
similar semantics, but set by presentity and left alone by PA
for policy filtering ("only show 'class=minimal' items when notifying low-bandwidth watchers")
Cf. Cascading Style Sheets (CSS):
"id" = unique across document
"class" = type of element

12. Proposal: Labeling Support class parameter/label: Identifier (id):
similar to <div class=X></div> semantics in HTML and CSS
one-to-many: one class, many tuples
each tuple can have at most one class
inherited (if supported in RPIDS)
used for filtering and policy
Identifier (id):
for identification (replace, edit, delete) of specific tuples
unique across all tuples for presentity
should not be re-used
e.g., time of initial creation of tuple