How to handle a sudden disconnection of the master on the peripheral (NRF8001)

Question

Hello Nordic team, 
 I am working on a BLE RedBearLab shield (nrf8001) mounted on an Arduino board. 
 Consider that a connection is correctly made from a Master app to my nrf8001 (Peripheral) . The master have already subscribed to an advertising characteristic (with a notify mod) and every thing is fine. 
 If the Master suddenly stop running (for exemple if the Master is out of battery or just crashed…) I would like to know the proper way to inform my nrf8001 board that the subscription of the advertising characteristic previously made is not valid anymore. 
 How can I do that ? My first idea was to sent a packet every X period of time from my peripheral board with an acknowledgement and if I haven’t received any response before a pre-determined time , I can consider that the connection is lost. Is there any other/better way to do that ? How can I know that there is no more valid connection on the peripheral side? 
 Thanks,
Regards,

Omnia · Accepted Answer

hello, 
 I am back. After several tests to understand why I don’t have any DisconnectedEvent on the peripheral side when I stop my iOS/OSX app (Central side). I was looking from the wrong side, the problem was coming from the Central side and not the one I suspected (Peripheral side). 
 I tried on both iOS 7 and Mac OSX 10.9.
It seems that CoreBluetooth keeps alive the connection during severals minutes after the link had been disconnected to the app. In other word the central still maintains a connection even if you stop the app (From the stop button of Xcode) and that’s why there is no DisconnectedEvent on the peripheral side. 
 Hope it will help someone.
Thanks for the nordic team support to guide me to understand where was the problem.

Omnia · Answer

Thanks for your answer, 
 All your sentences are correct, I mean, it's what is happening. 
 
 I not using any encryption on the link. 
 The master has to subscribe again (At each reconnection) to the Characteristics that are Notify or Indicate. 
 The subscription has to be done for every connection from the master when encryption is not used. 
 
 And effectively, if the master close properly the connection, the peripheral receive an ACI Disconnected Event to signal that the app has finished. 
 However, even if I think I understand what you said, what is the link between this and my problem?
My goal is to receive an event from the peripheral side when I lost the master. To be able to get that, do I have to do an encryption on the link (for example a paring without man-in-the-middle (MITM) protection would work)? 
 I am little bite confused about what you call encryption. Do you have any example or document to help me to understand this concept and how it will resolve my problem? 
 Thanks,

How to handle a sudden disconnection of the master on the peripheral (NRF8001)

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