Pairing/Bonding implications for ble_app_uart and ble_app_uart_central?

[Robin]

Hello once again Nordic World,

We are preparing code for production, and one of the last issues to resolve is how to "uniquely" connect our ble_app_uart peripheral based board to our customers iPhone.

Our board uses the NRF51822 MCU and is based on the PCA10028 board.  The code is built from SDK 12.3.

As current configured, our peripheral device will advertise and connect to the first central device (iphone) that finds it, which is, of course, a problem when there are several within BT range.  So we need a connection scheme that allows our peripheral to only be connected to by the owner's iphone.

Importing pairing and bonding to our apps seems excessive since we are not truly concerned with "data security".  However, it is acceptable given the following criterion:

   1.) The peripheral must either:

         a.) still accept unpaired/unbonded simple connections from our ble_app_uart_central based test board (firmware modified PCA10040), or

         b.) the paired/bonded connection must have a "backdoor" to not require re-registration of each new board that is to be tested.

   2.) When released to the customer, the iphone connection must classically pair and bond to only the customers copy of our boards, and

   3.) The effort to import the pairing bonding to our board and the 10040 should not be overly intensive.

Does anyone know if such a scheme is possible?

One alternative scheme I have considered is to add a unique ID to the advertised packet and have the customer phone app offer up those IDs found when scanning, and then store the selected device ID as the only "bonded" peripheral during the initial configuration of the iphone software app that communicates with our boards. 

I would greatly appreciate any critique and suggestions on the simplest way to achieve unique connection from a central to our peripheral board.

Thanks again to all in advance,

Robin @ TL

[ovrebekk]

Hi Robin

There is a whitelist feature in the BLE stack that allows you to limit which devices the peripheral will connect to. This list can contain up to 8 different devices, and it should be possible to put the users iPhone and the PCA10040 test board in this list (assuming the test board uses a static, known BLE address). 

The only question is how to do the initial bonding with the phone, when the the peripheral does not yet know the address of the users phone. 

Most likely you need to set the peripheral to connect to anything at this stage, and then configure the whitelist after you have connected to the phone for the first time, so that it will only connect to that phone in the future. 

A common way to handle the process of selecting a device on the phone is to use RSSI as a basis, and only connect to the device with the strongest signal (which is typically the device closest to you). 

Best regards
Torbjørn

[Robin]

Hello Torbjorn,

Thank you for the reply.  However, I don't quite fully understand what you are suggesting.  

Is what you are suggesting after additon of pairing/bonding, or can it be done as exists in the ble_uart apps?

My understanding is that the ble_uart example apps do not support pairing/bonding.  My preference is not to chase it any further that necessary to make the product simple and reliable for the customer.

I eagerly await your reply,

Thank you agian,

Robin @ TL

[Robin]

Hello again Torbjorn,

In researching how to get whitelist up and going I came across this great tutorial

Bluetooth Smart and the Nordic's Softdevices - Part 1 GAP Advertising

but the turorial has left me even more confused regarding setting up and starting advertising.  The tutorial calls out the the commands:

sd_ble_gap_adv_data_set, and

sd_ble_gap_adv_start

Neither of these commands are used anywhere in my code, which comes directly from the SDK 12.3 version of ble_app_uart.

There are 2 commands related to advertising in this code:

advertising_init, and

ble_advertising_start.

Are there multiple way of configuring and starting advertising, or what else might I be missing.

Thanks again,

Robin @ TL

[ovrebekk]

Hi Robin

Robin said:

Is what you are suggesting after additon of pairing/bonding, or can it be done as exists in the ble_uart apps?

My understanding is that the ble_uart example apps do not support pairing/bonding.  My preference is not to chase it any further that necessary to make the product simple and reliable for the customer.

There is no bonding in the ble_app_uart example, no, but it's still possible to add this on top. 

The problem of not bonding is that you have to do service discovery every time you connect, which will slow down the connection procedure. 

Bonding will complicate the firmware to an extent, but is normally better for the end user experience. 

And even if you don't properly bond you need some way to associate your peripheral to the phone, so that you can easily reconnect with a device you have previously been connected to. 

Robin said:

sd_ble_gap_adv_data_set, and

sd_ble_gap_adv_start

Neither of these commands are used anywhere in my code, which comes directly from the SDK 12.3 version of ble_app_uart.

There are 2 commands related to advertising in this code:

advertising_init, and

ble_advertising_start.

Are there multiple way of configuring and starting advertising, or what else might I be missing.

The new examples use the ble_advertising.c library as a wrapper around the sd_ble_gap_adv_xxx functions in order to abstract away some of the low level advertising setup. 

If you open ble_advertising.c you can see that functions such as sd_ble_gap_adv_start and sd_ble_gap_adv_data_set are called from here. 

You can bypass the ble_advertising module if you like and configure this on the SoftDevice level, but unless you have very specific requirements to the advertising behavior it is usually recommended to use the SDK modules. 

Best regards
Torbjørn

[Robin]

Hello again Torbjorn,

We have an interim solution for this.  You may close the case.

Thanks

Robin