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Re: 2.0 and Radio Impacts/battery efficiency

From: Roberto Peon <grmocg@gmail.com>
Date: Sat, 14 Apr 2012 14:11:45 -0700
Message-ID: <CAP+FsNcL=GmbMB5F9ByAF3EOP2iiKKCYk=O0vkduSArci6B4qw@mail.gmail.com>
To: Carsten Bormann <cabo@tzi.org>
Cc: Markus.Isomaki@nokia.com, salvatore.loreto@ericsson.com, zhong.j.yu@gmail.com, ietf-http-wg@w3.org
First: There needs to be better integration between the transport, app, and
hardware/radio on this in order to vastly improve the situation.

Second: Setting keep-alive to such low values can also adversely impact
battery, depending on the pattern of connection use, as it will increase
(significantly) latency for getting the user what they want. Additionally
many chat clients and/or ajax sites will use "hanging" gets, which return
perhaps every 30s. Even using a bidirectional stream (e.g. WebSockets),
this problem persists.

Until there is a study looking at what many websites do on devices from
various carriers, any supposition about reducing or increasing timeouts and
the impact on battery is just hypothetical supposition.

One thing is clear, however: Regardless of the usage pattern, use of a
proxy will reduce the number of extraneous radio wake-ups.

On Sat, Apr 14, 2012 at 1:07 PM, Carsten Bormann <cabo@tzi.org> wrote:

> On Apr 13, 2012, at 12:45, <Markus.Isomaki@nokia.com> wrote:
> > However, if the connections are closed after some idle period, for
> instance by a server timeout, that makes the radio wake-up an additional
> time.
> I haven't measured this, but looking at the docs leads to the following
> conjectures:
> The Apache 2.0 KeepAliveTimeout default was 15 seconds.  With the 17
> seconds the AT&T parameters take to power down the radio and the 2 s to
> power up again, this would lead to a total of 15+2+17 = 34 seconds to power
> down.
> The Apache 2.2 KeepAliveTimeout default is 5 seconds.  With any latency,
> this appears to make sure the radio has just been put to low power only to
> go through a 1.5 s transition to full power again (unless the FIN can be
> handled on the FACH -- I don't know).
> Summary: With the AT&T numbers cited here, you could do your mobile users
> a favor by setting KeepAliveTimeout to 4 or less seconds.
> (Find more about the 3G states and their timing in
> http://www.pasieronen.com/publications/haverinen_siren_eronen_vtc2007.pdf-- this has a much smaller T2 than the 15 seconds the Android docs cite.
> One interesting number in
> http://research.nokia.com/files/tr/NRC-TR-2008-002.pdf was that a single
> keep-alive exchange on their 3G network costs 9200 mJ (as opposed to 280 mJ
> on WiFi), about 0.7 mAh on a 3.7 V battery.  You might have some 2000 of
> those keep-alives in your cellphone battery before it is gone.  Ouch.)
> Gre, Carsten
Received on Saturday, 14 April 2012 21:12:14 UTC

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