[Standards] Binary data over XMPP

Dave Cridland dave at cridland.net
Wed Nov 7 12:56:31 UTC 2007

On Wed Nov  7 09:27:49 2007, Peter Saint-Andre wrote:
> As always, what are the use cases?
> If XML is black-and-white, I see:
> 1. Include a little dab of color -- an emoticon, a PNG avatar, a
> thumbnail for a file, a small inline image for whiteboarding, or
> whatever (something less than 50k and perhaps less than 10k). Here
> Base64 might be all we need, via data: or cid: URLs perhaps.
Yes, base64 is acceptable here, although bear in mind that over a  
charged-by-transfer medium - such as many mobile phone tariffs - that  
100k image is transferred as 133k, and 33k that you didn't really  
need to transfer sounds like an additional cost we could drop if we  
had the technology to do so. It's not a driver for it, though, I  

> 2. Attach a larger color sketch -- a file, the image for which a
> thumbnail is a representation, or whatever (50k to 1M?). I think we  
> use
> HTTP-PUT (perhaps via WebDAV) and jabber:x:oob, with IBB as a  
> fallback.
Right, we're into "would be very nice" territory here. 333k (or  
thereabouts) is a noticable chunk on my mobile bill, and it's around  
11 seconds of time on my (256k uplink) DSL.

> 3. Send a huge color canvas -- a music file, a podcast, a video, or
> whatever (1M+?). I don't know what we use for this.

Once we're into filesharing, then yes, we need either a binary  
streaming protocol (A binary variant of IBB), or else we want to ship  
the data out of band.

There's also a use-case you seem to have forgotten, which is the  
reason I raised this now:

4. XTLS and similar encrypted server-mediated client-client streams.

To send these via a peer-to-peer session negotiated via XMPP - like  
Jingle - strikes me as losing a fundamental benefit of XMPP, but it's  
also much cheaper in terms of bandwidth than sending them via the  
server right now.

I personally feel that if we're to say that XMPP truly supports end  
to end encryption, we need to ensure it's of near-equal cost to the  
current way of doing things.

Dave Cridland - mailto:dave at cridland.net - xmpp:dwd at jabber.org
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