[Standards] certification etc.

Dave Cridland dave at cridland.net
Thu Mar 29 15:26:03 UTC 2007


On Thu Mar 29 02:24:11 2007, Peter Saint-Andre wrote:
> Right. Unfortunately, it seems that some (many? most?) TLS 
> implementations do not support the compression option, so even if 
> the XMPP client and XMPP server support TLS, if their underlying 
> TLS library lacks support for compression there's not much they can 
> do.

This debate came up in Lemonade, since Lemonade introduces 
application level stream compression too. The summary is that on many 
devices that would benefit from compression, such as mobile handsets, 
the Nokia Internet Tablets, etc, there's no inherent ability for 
compression. However, there are third-party plugins available for 
both the older OpenSSL 0.9.7 that's in use on the tablets, and for 
Symbian, too.

In addition to the above, being able to distinguish from a flush 
through the compression algorithm, and a flush through TLS and the 
network, means that higher compression can be achieved in some cases. 
This probably doesn't apply to XMPP, since the data is relatively 
uniform from a formatting perspective, whereas in IMAP the switch 
between the protocol and the payload data can skew statistical 
compressors (such as the Huffman stage of DEFLATE) very heavily.

There overall consensus was that application-level stream compression 
is useful at least in the short term, although the better long-term 
strategy is to use TLS compression and "fix" the APIs.

Dave.
-- 
Dave Cridland - mailto:dave at cridland.net - xmpp:dwd at jabber.org
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Infotrope Polymer - ACAP, IMAP, ESMTP, and Lemonade



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