Android does not use Data Length Extension for L2CAP Coc

RE: Android does not use Data Length Extension for L2CAP Coc

Marco — Tue, 10 May 2022 12:50:57 GMT

Thank you Sigurd, I thought the effective values were on LL_LENGTH_RES, but now I understand each device puts its own in REQ/RES and the effective value is the minimum between the two.

After more testing I discovered that the Android device only switches to a 251 bytes TX size if a big ATT MTU is requested. Weird.

RE: Android does not use Data Length Extension for L2CAP Coc

Sigurd — Mon, 09 May 2022 09:14:22 GMT

Hi,

Yes, seems to be the Pixel phone not supporting sending longer than 27 octets packets:

iPhone in comparison:

RE: Android does not use Data Length Extension for L2CAP Coc

Marco — Mon, 09 May 2022 08:51:57 GMT

Sigurd Any thoughts?

RE: Android does not use Data Length Extension for L2CAP Coc

Marco — Wed, 04 May 2022 11:31:32 GMT

Hello Sigurd,

I don't currently have another device running Android 10 or higher (needed for L2CAP CoC APIs).

I'm attaching the logs.
Unfortunately, nRF sniffer drops basically all packets on iOS with the optimised parameters (MTU=240). I'm attaching a second iOS log with lower MTU=220 which is logged mostly fine, so you can get a better idea. Android would have the same fragmentation issue on MTU=220.

devzone.nordicsemi.com/.../Pixel-4-_2D00_-15ms_2C00_-MTU_3D00_240_2C00_-PHY_3D00_2M.pcapng

devzone.nordicsemi.com/.../iPhone-SE-2022-_2D00_-15ms_2C00_-MTU_3D00_240.pcapng

devzone.nordicsemi.com/.../iPhone-SE-2022-_2D00_-15ms_2C00_-MTU_3D00_220.pcapng

RE: Android does not use Data Length Extension for L2CAP Coc

Sigurd — Wed, 04 May 2022 11:11:45 GMT

Hi,

Have you tested with other Android phones? Do you see the same behavior there?

Could you upload a nRF sniffer log that shows the behavior, one for iOS and one for the Android?

https://www.nordicsemi.com/Products/Development-tools/nRF-Sniffer-for-Bluetooth-LE