handoff / handover indicator

Ravid Cohen ravidc at ottopia.tech
Mon Aug 30 08:05:02 UTC 2021

Hi Domi

Thank you for the clarification.

Best regards,

On Sun, Aug 29, 2021 at 8:51 PM Tomcsanyi, Domonkos <domi at tomcsanyi.net>

> 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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