handoff / handover indicator

Ravid Cohen ravidc at ottopia.tech
Tue Aug 31 05:29:41 UTC 2021

Hi Domi

Is there a way to get an indication when a RRC Connection Reconfiguration
is received using libqmi?

Best regards,

On Mon, Aug 30, 2021 at 11:05 AM Ravid Cohen <ravidc at ottopia.tech> wrote:

> Hi Domi
> Thank you for the clarification.
> Best regards,
> Ravid
> On Sun, Aug 29, 2021 at 8:51 PM Tomcsanyi, Domonkos <domi at tomcsanyi.net>
> wrote:
>> Hi Ravid,
>> Correct, the network continously receives measurement reports from the
>> modem, and then in case the threshold is below a certain signal-noise-ratio
>> or similar KPI then the basesatation instructs the modem to change. This is
>> usually where some “magic” could happen, vendors could introduce custom
>> KPIs that will affect if and how a handover will happen.
>> To be more concrete in a specific scenario let’s take LTE. There the
>> actual handover happens by using the RRC Connection Reconfiguration
>> message. Beforehand the source eNodeB aligns the handover with the target
>> eNodeB (e.g. sharing required security keys, checking if even the target
>> eNodeB would be able to accept this new user etc.) then after the ACK from
>> the other side it sends the Reconfiguration. In the background the UE’s
>> user plane (data) tunnels between the eNodeB and the core network are
>> switched as well to the new eNodeB.
>> In case you have access to the Qualcomm diag port of your modem that
>> could be made to stream out the over-the-air signaling messages to a client
>> program then you could potentially observe this happen, however there is
>> usually no way to easily know before it happens that it is about to happen.
>> Not all thresholds are advertised by the network, in fact most of them are
>> in the eNodeB’s configuration only.
>> However, if you are just willing to see if there was a handover lately
>> maybe you could query the current cell ID from the modem and see if it
>> changes. If you were doing a data transmission and during it the cell ID
>> changed you could be quite sure there was a handover imho.
>> Cheers,
>> Domi
>> 29.08.2021 dátummal, 19:22 időpontban Ravid Cohen <ravidc at ottopia.tech>
>> írta:
>> Hi Domi,
>> Thank you for the quick and detailed response.
>> I'm interested in the first scenario you described (ongoing service,
>> espaclly data).
>> If I understand you correctly, the change is triggered by the network
>> provider but the actual switch is made by the modem itself (according to
>> the operator instructions)?
>> If that is the case, maybe there's a way to catch this event/s?
>> Thanks you again,
>> Ravid
>> On Sun, Aug 29, 2021 at 8:08 PM Tomcsanyi, Domonkos <domi at tomcsanyi.net>
>> wrote:
>>> Hi Ravid,
>>> Firstly I think the most important is to get the terms correctly: so by
>>> handover do you mean handing over an ongoing service (voice or data) from
>>> one cell to another, or do you mean cell reselection in idle mode because
>>> of moving or change of radio conditions?
>>> The first one is actively triggered by the network to maintain
>>> continuity in the service as much as possible, the other happens
>>> autonomously by the baseband. Sadly both of them are quite hard to detect,
>>> because even though certain events are fired and thresholds are crossed
>>> these remain internal to the baseband firmware as far as I know.
>>> Kind regards,
>>> Domi
>>> > 29.08.2021 dátummal, 16:30 időpontban Ravid Cohen <ravidc at ottopia.tech>
>>> írta:
>>> >
>>> > 
>>> > Hey
>>> >
>>> > I'm not sure this is the right place for such questions, if not please
>>> refer me to the right place.
>>> >
>>> > I'm using a Sierra modem (em7565).
>>> > Is there a way to get notification before the handover process between
>>> two cells begins?
>>> >
>>> > Best regards,
>>> > Ravid
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