On 04/11/2017 11:21 PM, Denis Kenzior wrote:
Hi Jonas,
On 04/11/2017 03:48 PM, Jonas Bonn wrote:
Hi Denis,
On 04/11/2017 07:07 PM, Denis Kenzior wrote:
On 04/11/2017 03:18 AM, Jonas Bonn wrote:
The LTE atom should watch the network status and automatically
activate
the default bearer when the modem becomes registered to the LTE
network.
This patch adds a device callback, activate_default_bearer(), to allow
the device to start networking.
Nope, we're not doing it this way. Once we're attached to LTE there's
no need to activate a default bearer. It is already active. The
modem should tell us that this is the case.
Another issue is that the network is free to ignore our default bearer
setting, so you might be activating (or trying to) yet another context.
Doesn't QMI provide an equivalent of +CGEV?
I haven't found an equivalent. Right now it looks to me as though the
only way to set up a PDP context is to call the "Start Networking"
method. If I don't start networking, the packet status callback never
gives me a "connected" status. It's not enough to just power on the
modem... although that does get me registered to the network.
QMI is an ancient protocol, so maybe it simply didn't get extended for
LTE. Or we just don't know how to drive it properly. Is there an AT
channel ? Does that one report anything related to CGEV?
Furthermore, it doesn't matter what APN I use, I always get a usable
data-connection. "Get Settings" never returns an APN string, either,
which makes me that the network is ignoring my setting altogether and
just giving me a default bearer...???
The network is ultimately responsible for allocating an APN. It could
be blank or null or whatever. Or maybe we don't know the right magic
incantation.
Alright, I'm going to explain my understanding of how this works:
When the QMI modem registers to an LTE network, it negotiates a default
bearer using the "default settings". The default settings are taken
from the QMI WDS "default profile" which is presumably profile 1 by default.
Even though the network registration has taken place and the bearer is
in place, the QMI modem doesn't bring up the network interface. Calling
"get current settings" at this point gives you nothing.
At this point, you need to bring up the network interface by calling
"Start network". Start network takes a bunch of parameters but these
parameters are all ignored since the bearer is already set up.
I haven't tested this, but I suspect that calling "Start network" for
the same profile again will fail...??? A profile number corresponds to
a Context ID...??? Maybe...
If you need a specific setting for the default bearer (like APN), you
need to set it in the default profile before registering to the
network. This is what the LTE atom must take care of... and, hence, the
atom must be created
before setting the modem online.
For non-LTE, the bearer isn't set up until "Start network" is called, so
the usual context parameters can be passed to it at that time. Any
parameters that are omitted are taken from the default profile.
Given all of the above, for QMI this means:
i) When the netreg atom detects registration to an LTE network then we
can call "Start network" immediately.
ii) Start network will give us the packet-handle for the default
bearer. This can be held by the netreg atom.
iii) The packet handle survives until the network becomes unregistered
(even through a transition to UMTS,GPRS,etc networks).
iv) There is never any reason to call "Stop network" for the default
bearer because a network unregistration will achieve the same thing. If
the network becomes unregistered we can throw away the packet handle.
The gprs-context associated with the default bearer won't know the
packet-handle, so we need to make sure it doesn't try to call "Stop
network" for it's instance... but that's a detail, I think.
It seems that there exists a method to change the default profile
number... it's undocumented, though, AFAICT.
What's a bit unclear to me, though, is how this interacts with network
technology transitions... what happens when I move out of LTE coverage
and into a UMTS/GPRS network?
Questions? Feedback appreciated...
/Jonas
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