9:27 p.m.
Hi Mika,
> > I'm not quite sure what you mean here. There are many
> different cases, where the network can detach a UE from GPRS
> service. See possible detach causes in 24.008. Currently,
> oFono does not recover at all. Trying to figure out when GPRS
> is again available can get pretty complicated and the
> different detach causes require different handling. IMO, the
> simplest approach by far is to retry GPRS attach when someone
> actually needs a PDP context.
>
> So here's the problem, ConnMan is in charge of activating the
> context on
> Meego. ConnMan activates the context once we're attached. So how do
> you expect your 'on-demand' re-attach to work exactly?
ConnMan really should not care whether we are attached or not. Why do you need a trigger
in ConnMan, anyway? As far as I can see, a GPRS connection should only be activated if
some client of ConnMan requests it.
so what about the cases when roaming is allowed or not? These needs to
be taken into account and that is oFono's job. That is the reason why
ConnMan follows the attach state. Since we don't wanna activate a
context when roaming and data roaming is not allowed.
> Besides, 24.008 cause codes give us plenty of hints of
> whether / when to
> re-attach, and only a few of them require 'special' handling.
>
> I still think that we should come up with some strategy to re-attach
> automatically when detached by the network.
Even if you can come up with an algorithm, testing it is very very challenging. There are
plenty of differences in operator networks and it is very difficult to cover all cases.
Making sure that the algorithm works requires extensive IOT and Field testing. We really
don't want a case, where oFono fails to re-attach for whatever reason. We also
don't want the case where oFono has not yet attempted to re-attach (e.g. on a timer)
and a PDP context activation fails, even though GPRS would actually be available.
I don't think such an algorithm is hard. Either we are forbidden, then
we wait until we switch to a new cell. Otherwise we will just retry to
attach.
For the above reasons, retrying attach on PDP context activation
makes sense as a safe-guard, regardless of whether we have a re-attach algorithm or not.
We use on-demand attach in pretty much all our products (except for certain operator
specific variants) precisely because it is certain to work. No funny business. If there is
GPRS service, you get a connection. It is also an approach that should work with any AT
modem as well.
This is really not ConnMan's problem and I don't wanna make it ConnMan's
problem.
I am really against just pushing this problem off to someone else. And
in ConnMan we have even less information to decide what happens when
context activation fails. The algorithm to handle such rare error
conditions smoothly becomes more complicated than making this easier.
So I agree with Denis that we need to fix this inside oFono and just try
to intelligently re-attach.
Regards
Marcel