[whatwg] Bandwidth media queries

[Andy Davies]

Hi Matt,

You really want to know what the throughput is rather than just the
bandwidth and throughput is a bit of a PITA to work out in web
conditions...

Throughput is a mixture of available TCP connection time, bandwidth,
latency and packet loss, etc.

In theory you could measure it from the browser but there are a number
of issues, here are some examples:

A typical webpage is made up of many components, which are retrieved
via short, bursty conversations between the browser and server.

The initial TCP connections go though a 'slow-start' phase while the
client and server determine what's the optimal number of packets that
can be sent without being acknowledged. The number of packets inflight
and the latency effective set a cap on the throughput. So measuring
the resources that are downloaded first would probably under report
the available throughput

Multiple (sub-) domains confuse things further...

Assume you can effectively measure throughput from the first resources
to be downloaded (HTML, CSS etc), what happens if the images are on a
different domain e.g. a CDN? The throughput that's just been measured
isn't applicable to the CDN's domain.

Caching further complicates things as you can't use anything that's in
the cache to measure throughput (or can you?)

Although slightly tangential it's worth having a read of Mike Belshe's
"More Bandwidth Doesn't Matter (Much) -
http://www.belshe.com/2010/05/24/more-bandwidth-doesnt-matter-much/

I'm not sure I'd agree with Tab's comment that authors aren't the best
people to make decisions on what content should appear under different
throughput conditions though. If they aren't I'm not sure who is? If
it's the browser then the author still has to signal their intent to
the browser so they are effectively making the choice.

Cheers

Andy

@andydavies