nRF8001, ACK missing with indicate property

[David]

When sending data on a pipe with ACK (indicate), the acknowledgement seems to get lost if the device gets disconnected right after having sent that data. Is that a normal behaviour? How can I know if the data has been transmitted successfully?

The goal is to have a reliable data transmission where every packet is resent as long it is not acknowledged by the receiver. If there is an unintended disconnection (connection timeout) after having sent a data packet, no acknowledgement is received and the data will be resent after reconnection. This sometimes leads to a second reception of the same message...

How can a server (nRF8001) know that a data has been received if there is no ACK? What do I need to get a transmission where every message is reliably transmitted exactly once?

[David]

Thank you for this answer. The idea looks good, but unfortunately I can not confirm what you are suggesting :-/

When sending data on a pipe with ACK, I always get the DataACKEvent right after the DataCreditEvent at the next connection interval following the data transmission. Even when using a pipe without ACK, the DataCreditEvent occurs at the next connection interval. This is easy to see, you only need to set the connection interval to 2 seconds.

Is there some other configuration that could influence this behaviour? I would really like to use the radio level acknowledgement as you suggested, but for now there is no difference. Even when using the DataCreditEvent as a confirmation for successful transmission, I still get duplicate packets...

I cannot discard the duplicate packets on the peer side, because there is a possibility to send several identical packets which are all valid. I have no time-code or other counter which would allow me to tell that the received data is a re-transmission and not a new data packet.