Can a peripheral retrieve a phone's name after connected?

RE: Can a peripheral retrieve a phone's name after connected?

Hieu — Wed, 19 Jun 2024 15:58:46 GMT

Hi kpreiss,

Sorry, this took a while.

If I understand your concern correctly, it's that you cannot control when the 3rd party device will initiate service discovery, and thus simultaneous discoveries might happen, correct?

I could only go into a little depth with the NCS-based Peripheral. I cannot comment on the capability of the Central. I can only say that the Bluetooth Spec does not forbid simultaneous discovery.

For the Peripheral app here, the Zephyr Bluetooth Host allocates a new buffer each time there is a new GATT request. So, the failure conditions are somewhat like mallocs, where a lot of requests have been queued up.

Meanwhile, the remote Client can send at most one request at a time, and the app's own Discovery will also only queue one request at a time.

Additionally, the Central's GATT Server usually contains just the bare minimum GAP characteristics, so the discovery of the Central's Server will complete quickly.

Considering all of that, as long as EATT is not being used and the application does not perform other requests while performing the discovery, it shouldn't be an issue.

I setup a slightly modify pair of Peripheral UART and Central UART samples, where both devices try to discovery service as soon as they are connected. It works fine.

devzone.nordicsemi.com/.../c328916_5F00_concurrent_5F00_discovery.zip

Please remember that this is meant to be a demonstration and not a representative for all cases. Thorough testing of your system is always necessary.

RE: Can a peripheral retrieve a phone's name after connected?

kpreiss — Thu, 13 Jun 2024 20:45:40 GMT

Thank you Hieu,

The simultaneous discovery is a requirement because we already have 3rd party developers who are querying the GATT server in the peripheral. If it's not supported, would an error be returned informing the higher level application to retry characteristic discovery?

RE: Can a peripheral retrieve a phone's name after connected?

Hieu — Thu, 13 Jun 2024 20:37:34 GMT

[quote user="kpreiss"]What is the process for finding the central's server characteristics?[/quote]

The process for the Peripheral discovering the Central's GATT Server is exactly the same as the one for the Central discovering the Peripheral's GATT Server.

[quote user="kpreiss"]Can the central be discovering the characteristics in the peripheral GATT server at the same time the peripheral is discovering the characteristics in the central GATT server?[/quote]

I am not actually very sure myself. Is this simultaneous discovery an important requirement? Discovering a Central's GATT Server is usually very fast, because such server usually only has the GAP Service.

[quote user="kpreiss"]Do you have nrf Connect SDK examples of this?[/quote]

You can just refer to the GATT Client code in Central samples.

[quote user="vthieu"]I am trying to understand the spec to see if the GATT Server is always required. I will get back to you on that soon.[/quote]

A colleague helped me found that the spec does require that the Central has a GATT Server. You can expect to find the GAP Service and Device Name Characteristic.

RE: Can a peripheral retrieve a phone's name after connected?

kpreiss — Thu, 13 Jun 2024 14:50:48 GMT

Ok, thank you. What is the process for finding the central's server characteristics? Can the central be discovering the characteristics in the peripheral GATT server at the same time the peripheral is discovering the characteristics in the central GATT server? Do you have nrf Connect SDK examples of this?

RE: Can a peripheral retrieve a phone's name after connected?

Hieu — Thu, 13 Jun 2024 13:00:07 GMT

Hi kpreiss,

If the central device hosts a GATT Server, there will be a mandatory GAP Service, where the Device Name can be read (refer to Bluetooth Specification, Vol 3, Part C, Section 12).

I am trying to understand the spec to see if the GATT Server is always required. I will get back to you on that soon.

Similarly, the GATT Server could also include an optional Device Information Service, where the Device Name is also a characteristic.

Hieu