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Re: ACTION-961: usefulness of multipart-mixed

From: Luca Passani <passani@eunet.no>
Date: Wed, 27 May 2009 15:10:43 +0200
Message-ID: <4A1D3BD3.4090001@eunet.no>
To: Mobile Web Best Practices Working Group WG <public-bpwg@w3.org>

I disagree that multi-part makes such a huge difference for 3G phones. 
It does not.

If you build your pages by:

1)  allocating space for the pictures in the img tag (height/width 
attributes),

2) adopting well-formed markup and

3) keeping CSS in the page (and not external as BP wrongly recommends),

then users will perceive the page as equally fast, or even faster, since 
XHTML loads faster than the full bundle of  XHTML/CSS/Pictures.

I understand that some companies want to present multipart support as 
something that gives extra value to their platform, but for regular 
developers supporting multipart introduces way too many hurdles to make 
sense. Even assuming they have a framework to automatize the packaging 
of their pages, which devices support multipart and which do not is NOT 
public information, i.e. they have no path to creating multipart which 
works reliably.

In short, I would be disappointed if W3C recommended that buying from 
Ericsson is a best practice :)

Luca

Magnus Lönnroth wrote:
> Hi, delivering multi-part MIME digests has been and still is an important part of optimizing performance in our installations. The main reason for developing this is the latency in 3g networks compared to wired broadband or wi-fi. It must of course be fully transparent and not affect content or content design in any way. One important aspect is to have detailed knowledge of the device's own caching capabilities and support for digests so that subsequent deliveries not include content that is already available (cached) on the handset. If full digests are delivered with each request I agree that the benefit is questionable. But if you have a good implementation with device knowledge the improvement is significant. 
>
> thanks,
>
> Magnus Lönnroth
> Head of Development
> Service Delivery & Provisioning, Ericsson ///
>
>   
>> -----Original Message-----
>> From: public-bpwg-request@w3.org 
>> [mailto:public-bpwg-request@w3.org] On Behalf Of Luca Passani
>> Sent: Tuesday, May 26, 2009 11:49 PM
>> To: Mobile Web Best Practices Working Group WG
>> Subject: Re: ACTION-961: usefulness of multipart-mixed
>>
>>
>> Multipart was a useful mechanism to deliver a full page in one shot. 
>> Vodafone leveraged multipart for its vodafone live service on 
>> devices which supported it. Multipart allowed for snappy (or at least
>> "2002-snappy") display of the top page, which looked great as 
>> compared to everything WAP had represented until that day.
>> There was no way to know whether multipart was properly 
>> supported by a device, except testing on that device. 
>> Notably, many devices declared multipart support in headers 
>> and UAProfs, but the information was not reliable at all. I 
>> recall that I never managed to get multipart to work on a 
>> Nokia device (still vaguely curious about whether there was a way).
>> Vodafone maintained its own db with this info for devices in 
>> its portfolio. Not sure if they still do. Probably not. Too 
>> much effort for too little value.
>>
>> 3G networks and faster browsers make the use of multipart 
>> much less relevant, particularly because pages become much 
>> harder to build and maintain if multipart is in the middle. I 
>> made space for multipart in WURFL back in 2003, but the 
>> community did not really follow: nobody was using it obviously.
>>
>> Luca
>>
>> Tom Hume wrote:
>>     
>>> I took an action a couple of weeks ago to look into multipart/mixed 
>>> MIME types, to see if they might be usefully related to 
>>>       
>> sections 3.4.6 
>>     
>>> and 3.4.7 of MWABP[1] (ACTION-961). In particular it would seem 
>>> helpful to be able to bundle many images up into a single HTTP 
>>> request, avoiding unnecessary round trips to download a set 
>>>       
>> of them. 
>>     
>>> The current advice is to combine related images into a single file, 
>>> download this, and use CSS positioning and clipping to 
>>>       
>> render parts of 
>>     
>>> this file. multipart/mixed would provide another route for 
>>>       
>> downloading 
>>     
>>> many resources at once.
>>>
>>> The only reference I can find to mobile usage of multipart-mixed is 
>>> this tutorial from OpenWave:
>>>
>>>
>>>       
>> http://developer.openwave.com/dvl/support/documentation/technical_note
>>     
>>> s/multipart.htm
>>>
>>> From running this experiment with desktop browsers, multipart-mixed 
>>> doesn't seem to be well supported. I've set up an HTTP response 
>>> matching the above and found that:
>>>
>>> - Firefox and Opera render the second page in the message
>>> - Safari doesn't recognise it as HTML and downloads it
>>> - IE renders content from both pages
>>>
>>> I've also got a question of how, from within CSS or similar, an 
>>> individual part of a multipart-mixed message might be uniquely 
>>> referred. The only reference I can find for a URL-scheme for such 
>>> things is a scheme for references to body parts of messages, which 
>>> date back to 1997 or earlier, and seem to be designed with 
>>>       
>> HTML email 
>>     
>>> in mind:
>>> http://www.ietf.org/rfc/rfc2392.txt
>>>
>>> Beyond the Openwave tutorial, and the following tool which 
>>>       
>> exists to 
>>     
>>> create these messages:
>>>
>>> http://www.umts-tools.org/docs/multipart/
>>>
>>> ...I can't find any other reference to them; and it's not a 
>>>       
>> technique 
>>     
>>> I've come across myself. Am I missing something obvious here? From 
>>> where I'm sitting this looks like a barely-used, poorly- supported 
>>> technique which I'd hesitate to consider a best practice - 
>>>       
>> though it 
>>     
>>> might be handy if it worked.
>>>
>>> Tom
>>>
>>> [1] http://www.w3.org/TR/2009/WD-mwabp-20090507/#d1e8981
>>>
>>> --
>>> Future Platforms: hungry and foolish since 2000
>>> work: Tom.Hume@futureplatforms.com
>>> <mailto:Tom.Hume@futureplatforms.com> play: tomhume.org 
>>> <http://tomhume.org>
>>>
>>>
>>>       
>>
>>     
>
>
>   
Received on Wednesday, 27 May 2009 13:11:30 UTC

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