Does BLE retransmission happen in same connection interval?

[BOZHENG]

Hi All

I am now developing BLE application on nRF52840 DK. I have a question about BLE retransmission process.

When master sends a packet to initiate a connection event/interval, but due to interference, slave cannot receive it. Thus, there will not be a packet back to master from slave. Does master retransmit that packet in this connection event/interval or next one? If master retransmit that packet in the same connection interval, when will it do it?

Thanks in advance.

[Vidar Berg]

Hi,

The master will attempt retransmission on the next connection event if the packet is not received by the slave. You may refer to  Vol 6, Part B, section 4.5 of the BT core specification for more details.

[BOZHENG]

Hi, thanks for your answer.

But if we consider about anchor point, the slave does not receive the first packet from master, it means the anchor point is not synchronized. How do master and slave decide the beginning of their next connection interval?

[Vidar Berg]

The first packet at the start of a new connection event, or first data packet after a connection request (ie before the connection is established)? Anyway, the Window widening (section 4.5.7) accounts for clock drift and the master and slave should not drift apart that fast.