[Standards-JIG] proto-JEP: Flagging the Primary Resource

Ian Paterson ian.paterson at clientside.co.uk
Thu Sep 29 10:20:15 UTC 2005

As I've understood it so far, there are two reasons for this JEP:

1. The server is in a better position to know which resource (with the
same presence priority) is the primary. For example, it knows which
resource sent the last message stanza, whereas subscribers only see the
messages that are addressed to them.

2. Use cases exist where another client MUST know exactly which resource
the host server considers is the primary.

I haven't understood the use cases for point #2. Could someone please
explain one in a bit more detail for me. :-)

> I'm not entirely sure if adding a new element
> to specify the most available is the best way. 

Yes, I'm nervous about any proposals to put extra content in presence
stanzas (they are very bandwidth sensitive). How about we document a
simple convention like:

"If two resources have the same priority then subscribers SHOULD
consider the primary resource to be the one that they last received a
<presence/> stanza from."

Another advantage of this approach (in addition to not requiring
<presence/> content) is that whenever the primary resource changes (to
another resource with the same priority) the server only needs to send a
single <presence/> stanza. (The current proposal requires two stanzas to
be sent, one with and one without the <primary/> element.)

- Ian

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