8:27 p.m.
Hi Marcel,
I somehow missed your other comments on this mail. More responses below.
> 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.
Mostly that would be just a waste of power. Some of the errors are PLMN or LA specific, so
retrying at cell change would be redundant. A proper retry strategy would have to be based
on the detach reason and any subsequent attach failure causes. In general, activating the
RF all the time, when no-one has even requested a PDP context is simply bad idea. There
are better uses for the battery power.
And yes, coming up with an algorithm (whatever it is) is probably easy enough. Making sure
it works with all the networks and modems out there is the hard part.
Otherwise we will just retry to attach.
That's also tricky. What do you do if the attach attempt fails? Retry again? How
often? Use some kind of backoff?
> 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.
No-one is proposing to. You're actually making this ConnMan's problem by
monitoring the GPRS attach status. If ConnMan needs a trigger, it should be based on
network registration status alone.
And
in ConnMan we have even less information to decide what happens when
context activation fails.
Unfortunately, oFono cannot hide context activation failures from ConnMan. ConnMan will
just have to cope, regardless of what we do with attach.
The algorithm to handle such rare error
conditions smoothly becomes more complicated than making this easier.
As far as I can see, the approach I'm proposing is simpler than the one you and Denis
are proposing.
So I agree with Denis that we need to fix this inside oFono
and just try
to intelligently re-attach.
As I already explained to Denis, it's not really a choise between one or the other.
Some opearators require autoattach, some require on-demand attach and some require a UI to
change the mode. All of these should be supported. So, by all means develop a re-attach
algorith. It won't be easy to maturize, though. Using context activation requests as a
triggers to retry attach simply makes a lot of sense as a safe-guard, even if we're in
autoattach mode. If anything, it removes one potential failure case.
Br,
MikaL