handoff / handover indicator

Ravid Cohen ravidc at ottopia.tech
Tue Aug 31 06:54:14 UTC 2021

Hi Domi,

Thanks for the quick reply.

Best regards,

On Tue, Aug 31, 2021 at 8:51 AM Tomcsanyi, Domonkos <domi at tomcsanyi.net>

> Hi Ravid,
> Not that I know of, no. Sorry.
> Without libqmi by directly getting radio traces from the diag port of the
> modem you could probably observe it, however you must check its contents,
> because this message is used for a lot of purposes, not only handover.
> Tools for extracting radio traces include diag-parser, scat, qcsuper (all
> on github).
> Cheers,
> Domi
> Az iPhone-omról küldve
> 31.08.2021 dátummal, 7:29 időpontban Ravid Cohen <ravidc at ottopia.tech>
> írta:
> Hi Domi
> Is there a way to get an indication when a RRC Connection Reconfiguration
> is received using libqmi?
> Best regards,
> Ravid
> 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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