Re: ACTION-961: usefulness of multipart-mixed

Magnus & Tom,

While not a regular contributor, I did want to add a bit of perspective on
this topic.

First I must concur with Magnus that MIME multipart is still in use and can
improve the user¹s experience in page load times as a round-trip latency
reduction tool.  While it can be a network optimization as Magnus describes,
the benefit is actually greater if done at the page source, thus eliminating
the multiple round trip latencies between the mobile network gateway / proxy
and the CP as well as from the handset across the mobile network.

Sprites / Composite images are not comparable; they only offer improvement
for static, decorative images.  If the multiple images/parts of a page are
dynamic content (news photos, album art, etc.) multipart still provides
benefit where sprites would not.  It also provides the delivery performance
benefits of embedded CSS with the flexibility of a linked style sheet.

Being a content type, use of multipart is independent of Content-Encoding.
So it¹s not required that multipart payloads be gzipped, though doing so may
be worthwhile where it is also supported by the device.

There are cases, as Luca describes, where devices advertise support in HTTP
headers but don¹t necessarily handle it well.  So device awareness and the
ability to override the devices¹ claim of support is necessary.  However, I
don¹t believe this is significantly different from other advertised device /
browser capabilities (CSS2 positioning, for example).

The degree of difficulty may make multipart debatable as a best practice,
but I don¹t consider it irrelevant ³from the content provider¹s point of
view².

Hope this helps...

John Hardi
Dir, Technology Strategy
Motricity, Inc.

On 5/27/09 12:22 AM, "Magnus Lönnroth" <magnus.lonnroth@ericsson.com> wrote:

> Yes, I'm referring to HTTP responses. A proxy is needed. URL-rewriting is
> needed. I'm not sure if the context for my response was appropriate - I was
> just reacting to the previous statements saying that packaging content in
> multi-part MIME digests was kind of obsolete. From the content provider's
> point of view MIME multi-part digests are irrelevant and have probably always
> been so. From the service provider's point of view it's still an important
> network level optimization. But it should be completely transparent and hence
> most likely not part of a best practices discussion. Sorry if I'm confusing
> matters.
>  
> /Magnus 
> 
>>  
>>  
>> 
>>  From: Tom Hume  [mailto:tom.hume@futureplatforms.com]
>> Sent: Wednesday, May 27, 2009  8:51 AM
>> To: Magnus Lönnroth
>> Cc: Luca Passani; Mobile Web  Best Practices Working Group WG
>> Subject: Re: ACTION-961: usefulness  of multipart-mixed
>> 
>>  
>> Magnus 
>> 
>>  
>> Are you referring to using multi-part/mixed for HTTP responses from a web
>> server?
>>  
>> 
>>  
>> If so, can you explain how resources within a multi-part/mixed HTTP  response
>> are referred to from each other, or from outside the response?
>>  
>> 
>>  
>> Tom
>> 
>>  
>> 2009/5/27 Magnus Lönnroth <magnus.lonnroth@ericsson.com>
>>  
>>> 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>
>>>>> >  > <http://tomhume.org>
>>>>> > >
>>>>> >  >
>>>> >
>>>> >
>>>> >
>>> 
>> 
>>