On Sat Feb 16 10:18:37 2008, Fabio Forno wrote:
Did some homework about EXI.
As did I - not that I'm claiming expertise quite yet. Some random notes follow.
I basically agree that we don't want to be doing this as XEP-0138, for a number of reasons, including it being an additional round-trip, but it works as a way of doing some experimentation.
What's currently concerning me is that a single schemaID option may be present, which indicates the single schema you've used for encoding.
Currently, we have no such single schema, and in the absence of such a schema, my understanding is that the bulk of the performance of EXI is down to its usage of DEFLATE - thus somewhat contradicting those people who've been telling me that DEFLATE is a Bad Thing for mobile devices, but EXI is fantastic. Ho hum.
The schemaID is non-restrictive - that is, that use of a schemaID wouldn't restrict usage of other schemas. So specifying bling use of EXI is insufficient for our purposes - we need to define a single schema which represents the overall schema used for the stream.
On top of that, the more accurate that schema is, the better compression will be achieved - out performing DEFLATE by a reasonable margin. This suggests that the more we put into our master schema, the better - so we probably want more than one of them, to allow for different deployment types to handle their cases optimally.
So it seems to me that if we were using EXI in XEP-0138, a single "exi" algorithm isn't sufficient to grant interoperability. Instead, we need a method for negotiating schemaIDs, codecs, and the various other random options. In particular, we probably want the precompression option available, for the rather odd case of doing DEFLATE in TLS, but EXI in XEP-0138.
It occurs to me that for certain schemas particularly heavy in markup, like SVG whiteboarding, the compression potential is pretty high, but for quite a few typical uses of XMPP - like IM itself - the bulk of the compression will be down to DEFLATE anyway, suggesting that doing EXI in these cases isn't worthwhile - although I may be wrong here.
Dave. -- Dave Cridland - mailto:[EMAIL PROTECTED] - xmpp:[EMAIL PROTECTED] - acap://acap.dave.cridland.net/byowner/user/dwd/bookmarks/ - http://dave.cridland.net/ Infotrope Polymer - ACAP, IMAP, ESMTP, and Lemonade
