Packet loss during ISO transmission when advertising

Question

Hi, 
 Bug: 
 With a connected ISO connection between two devices X and Y: 
 
 X acts as a peripheral. It's the ISO server and it is transmiting iso data to Y. 
 Y is multirole. It connects to X and establish an ISO connection to receive ISO data. 
 
 As long as Y only receives data, the communication is stable (no packet loss). As soon as Y advertises (bt_le_adv_start), Y does not receive all packets. 
 
 Increasing advertising interval, decrease packet loss. 
 Decreasing advertising interval, increase packet loss. 
 
 Environment: 
 
 OS: Linux 
 Toolchain zephyr-sdk-0.16.8 
 NRF5340DK 
 NCS 2.7 (sdk-nrf v2.7.0 and zephyr v3.6.99-ncs2) 
 
 How can solve this issue, which causes too many packet loss ? 
 Thank you

yuxuan.cai · Accepted Answer

Hi, 
 Sorry that it took some time. 
 I've managed to reproduce the packet loss you mentioned, and after discussions with the team, I believe it has to do with how the data are provided. 
 In your application, the SDUs are provided to the controller with sequence numbers. When an SDU is provided too late, the controller will either drop the data or send it in the next event. An SDU can be provided too late due to the asynchronous nature of the HCI interface, or in your case, the interference from an ongoing advertiser. 
 To address this, you could use the "Time of Arrival" mode mentioned here by setting the sequence number to 0 when calling bt_iso_chan_send(). With this I observed no missing packets locally. 
 If you'd like to learn about the "Timestamp" mode, please check out the iso time sync sample .

Cheers, 
 Yuxuan

Packet loss during ISO transmission when advertising

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