[Standards] Presence Priority Implementation Guide

JD Conley jd.conley at coversant.net
Wed May 9 01:33:19 UTC 2007


This has been brought up before, but didn't find any definitive answers
with a search. What should we do about presence priorities in desktop
XMPP instant messaging applications? Managing priority is fairly
straightforward when you control all client implementations used by a
bare JID, but in a heterogeneous client environment it is more difficult
as each developer chooses his/her own path and only learns by spying on
what others do. I think presence priority is something that should be
covered in the implementation guide so the actual values become more
uniform on the network. We currently do pretty basic priority
management, but I have some thoughts on a better implementation I hope
others implementations might help refine.

 

Priority is typically used by both clients and servers to determine
which resource is most likely to be the one you want to interact with.
This could be for routing messages sent to bare JID's, or deciding which
presence status to display in a contact list. So, after much deep
thought and implementation trial/error, here is my proposal.

 

Unless a user explicitly specifies she does not want to receive any
messages, never set the priority below 0.

 

In desktop software, presence priority is based first on user input
activity. It is more likely that if a user is active, she will be there
to respond to a message, regardless of the presence status that is set
in the client software. The actual times may vary based on
implementation, but the general idea is to have four base values:

 

User input idle less than 1 minute: 100

User input idle more than 1 minute: 80

User input idle more than 5 minutes: 60

User input idle more than 30 minutes: 40

 

When these idle thresholds are met, presence should be broadcast.

 

The current show value is then applied.

chat: -4

none (normal/available): -4

dnd: -4

away: -8

xa: -12

 

Thus, if a user has been idle for more than 30 minutes and has a status
of "xa", her priority is 28 (40-12). If a user has been idle for more
than 30 minutes and has a status of "away" her priority is 32 (40-8).

 

By starting at a high number and leaving padding between each show
value, we leave room for implementations to add additional rules to
adjust priority. Dnd has a higher priority than away and xa because,
although the user does not want to be disturbed they are more likely to
be at the dnd resource than the away or xa resource. It is up to the
client implementation to insure they are not disturbed per the user's
configuration. A show of dnd uses the same priority as none and chat
since you are likely equally available, you just don't want to be
disturbed.

 

Priority and, optionally, show values are adjusted automatically based
on common "away from the computer" events: system input idleness (how
long since the user interacted with the system), when a session is
locked, or a session screen saver is active. When these events occur,
the priority rules must be processed again. For Example, my client is
configured to go to a show of away after 5 minutes with a status of
"AFK". After 30 minutes it is set to a show value of xa and a status of
"AFK for a long time". When my system is locked or the screen saver
comes on, my client automatically adjusts my show value to away and a
status of "Not here". Important: even if an implementation does not
change status messages or show values after these "away from the
computer" events it must still adjust its priority as defined above.

 

After the "away from the computer" rules are processed, the relative
availability of your peer resources is taken into account. If any peer
was more recently more available (had a more available show value than
your current value - chat, none/dnd, away, then xa) and has a
non-negative priority, subtract 20 from your current priority. For
example: I'm logged in at home and work. At home I last announced
available presence 4 hours ago. My software at home never puts me into
"xa" and instead decides I am "away" after 30 minutes. Home priority is
now 32 (40-8). At work I last announced available presence 3 hours ago
with a "none" show value. I go to lunch at work but it is configured to
reach a show value of xa after 30 minutes. Its priority is now 28
(40-12). However, since work was my last active resource, when my home
resource receives the broadcast from work it adjusts itself to a
presence priority of 12 (32-20). The purpose of this is to insure that
only the most recently available resource above more available than
away/xa is the one that takes the higher priority.

 

It is important to never adjust your priority relative to the priority
of a peer resource without taking much care. Doing so  can cause a
"race" for the highest or lowest priority (depending on the relative
direction your adjusting).

 

-JD

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