[maemo-users] Power consumption and WLAN APs

From: Frederic Crozat fred at crozat.net
Date: Mon Jul 21 23:08:38 EEST 2008
On Mon, Jul 21, 2008 at 11:39 AM, Kalle Valo <kalle.valo at nokia.com> wrote:
> "ext Frederic Crozat" <fred at crozat.net> writes:
>>> What power-management issues have you seen affecting battery life ?
>> I think it is usually caused by interoperability deficiency between
>> 770/n8x0 and some routers wifi chipset regarding PSM (Power Saving
>> Management) part of wifi specification.
> Exactly. The problems stems from the fact PSM was (and still is?)
> mostly unused by the windows laptops. So it seems that some AP
> manufactures decided to omit the testing of the PSM implementation
> altogether.
> Why is PSM so fragile then? Since I can't sleep (jet lag, argh), I'll
> write a bit about this.


wow, thanks for the detail explanations. I kind of better understand PSM issues.

>> I'm seeing this kind of issue between my work AP (Linksys) which have
>> working PSM and my home AP (Freebox, a set-top-box provided by my
>> ISP), where PSM is not working properly with a maximum uptime of 8h
>> when wifi is on.
> It sounds like PSM is not working at all with your home AP.

Yeah, I figured that ;)

However, Freebox engineer told me he could see PSM going up and down
on the AP side.

>> A first bug was found in ralink proprietary driver which was losing
>> AP association after some time in PSM mode, which was fixed by
>> Ralink.
> Hmm, I would first suspect that the AP is not really buffering all
> frames. I have seen APs which periodically send Null frames to check
> that the client is really alive. Maybe the AP vendor forgot to check
> if the client is sleeping when they send the Null frame? Wouldn't be
> the first.

I've forwarded your email to Freebox engineer ;)

>> If Eero or another Nokia hackers have some information which might
>> help Freebox engineers to track the issue, I'll be happy to serve as a
>> proxy.
> Dealing with vendors is very slow, it takes hours and hours of work,
> consisting mostly writing emails. I simply don't have time for that,
> and I rather write code than email.
> But what I could do is to analyse the problem myself. It would take
> only an hour or two, including writing a small report about the
> problem which I can send everyone interested (hopefully this includes
> the vendor). So if you would be able to convince the vendor to send
> the AP for a loan? If that's not possible, are you coming to Maemo
> Summit? If I manage to come and you can take the AP with you, I could
> take a look at it onsite.

Unfortunately, it won't be possible because Freebox (the name of
set-top-box = ADSL modem + wifi mimo router + many other nice things)
can only work when they are synchronized over ADSL with Free ISP
DSLAM. So, even if we could send you a Freebox, you couldn't do
anything with it :(

Anyway, I've pinged Freebox engineer in hope they might have a clue on
the issue.

> BTW, is there a bug about this? If not, please file one. I'll forward
> it to our IOP testers so that they could try get access to the AP as
> well.

Done : https://bugs.maemo.org/show_bug.cgi?id=3481

Frederic Crozat

More information about the maemo-users mailing list