Multiple Central devices sharing the load

RE: Multiple Central devices sharing the load

Hung Bui — Mon, 17 Jul 2023 07:54:47 GMT

Hi Bob,

Yes, it's possible to get RSSI from the scan request.
You can take a look here: S132 V6, How to get BLE_GAP_EVT_SCAN_REQ_REPORT event?

However, if the central send a Connect request, it's not possible for the application on the peripheral to choose to accept it or not.

You may need to implement some mechanism to not accept connect request initially (non-connectable advertising for example) , then start applying a whitelist before you switch to connectable advertising. Or you can do directed advertising, but that requires bonding.

RE: Multiple Central devices sharing the load

rbelli — Fri, 14 Jul 2023 15:26:48 GMT

Hello

We always send the scan request from the central. Can the peripheral see the RSSI of this packet?

Thanks

BoB

RE: Multiple Central devices sharing the load

Hung Bui — Fri, 14 Jul 2023 14:18:22 GMT

Hi again,

Please be aware that the peripheral can not "choose" which central to connect to.
It's the opposite, the central dictate the connection establishment.
The central scans for advertiser (peripheral) and chooses the advertiser to connect to.

Unless whitelisting is used, the peripheral will accept any connect request from any central.
It can, however, disconnect the central after the connection has been established.

You can try the approach to allow multiple central to connect to, but it would make the application more complex and requires the peripheral to continue advertising after a connection has been established.

RE: Multiple Central devices sharing the load

rbelli — Fri, 14 Jul 2023 13:45:20 GMT

It there a way for the peripheral to retrieve identifying information from the central device and also get an RSSI value before making a connection?

That would allow the peripheral to choose the one to connect to. What would be the best way of having the peripheral announce its intention to be connected in this case?

Would establishing multiple connections to central devices and choosing the one to use for a data conduit work better or easier?

Thanks

BoB

RE: Multiple Central devices sharing the load

Hung Bui — Fri, 14 Jul 2023 08:19:23 GMT

Hi Bob,

By default the peripheral has no mechanism to choose the central with stronger signal (unless you implement something like that).

The selection is more of "natural selection" , the central which is closer to the peripheral has more chance to capture the advertising packet and more chance that the connect request arrive successfully to the peripheral when signal is strong.

For the central with longer distance or weaker RF link budget (can be because wrongly tuned antenna etc) has more chance of corrupted packet, preempted signal.

RE: Multiple Central devices sharing the load

rbelli — Thu, 13 Jul 2023 14:35:51 GMT

We are only filtering on a UUID in the central device. No whitelisting is used on either end.

[quote userid="2121" url="~/f/nordic-q-a/101810/multiple-central-devices-sharing-the-load/436217"]Other than that, is there any chance that the "unpreferred" device has weaker signal ? For example it's too far away to establish a connection ? Or signal was too week to compete with the signal from the preferred central ? [/quote]

We do see that happening and lose some data. We also see them cluster to one when we have two gateways next to each other.

[quote userid="2121" url="~/f/nordic-q-a/101810/multiple-central-devices-sharing-the-load/436217"]If you turn off the preferred central would the peripheral connect to the unpreferred one ? [/quote]

Yes.

What is the easiest way to establish a connection to a stronger central? Can this be done solely in the peripheral?

Thanks

BoB

RE: Multiple Central devices sharing the load

Hung Bui — Thu, 13 Jul 2023 11:05:26 GMT

Hi Rbelli,

I can't think of any other reason why there is a preferred central except for accept list filter (whitelisting). Do you have any accept list filer in the peripheral/central ? This limit the devices that can connect to your peripheral/central.

Other than that, is there any chance that the "unpreferred" device has weaker signal ? For example it's too far away to establish a connection ? Or signal was too week to compete with the signal from the preferred central ?

If you turn off the preferred central would the peripheral connect to the unpreferred one ?