About the multiple ACKs in ATT MTU Throughput Example

RE: About the multiple ACKs in ATT MTU Throughput Example

dejans — Thu, 28 Apr 2022 08:21:27 GMT

Hi,

[quote user="EthanJia"]Is this common for the Sniffer to lose track of so much packets?[/quote]

It is not common for the sniffer to lose many packets. Since you have some issue with a sniffer, consider swapping DKs or replacing sniffer with a new DK. Please let me know whether you still experience drop in the throughput.

[quote user="EthanJia"]Meanwhile, my project is very time-critical, so are there any methods to disable ACKs in the Link Layer?[/quote]

There is no way to disable ACKs in the link layer in the SoftDevice.

Best regards,
Dejan

RE: About the multiple ACKs in ATT MTU Throughput Example

EthanJia — Wed, 27 Apr 2022 16:26:22 GMT

Hi Dejan!

Thanks! Yeah I think you are right. After adding all the ATT MTU packet sizes and comparing with the theoretical sum, I found that the sniffer actually missed lots of packets. Hence, the multiple ACKs should be caused by Sniffer's misses. Is this common for the Sniffer to lose track of so much packets?

Meanwhile, my project is very time-critical, so are there any methods to disable ACKs in the Link Layer? I suppose for each connection interval without ACKs, there would be at least 344μs saved. Although right now the ATT layer ACK is disabled by using notifications instead of indications, the LL will automatically send ACKs.

Best regards,

Ethan

RE: About the multiple ACKs in ATT MTU Throughput Example

dejans — Wed, 27 Apr 2022 15:52:02 GMT

Hi,

Based on the log, there might not be retransmissions, but missing packets from the master. This could indicate some problem with the sniffer.

In your case, many packets are sent per connection event. You could consider reducing the connection interval to around 30 ms or less and see if the situation improves.

In order to confirm throughput reduction or sniffer problem, consider using the log from both sides.

Best regards,
Dejan

RE: About the multiple ACKs in ATT MTU Throughput Example

EthanJia — Wed, 27 Apr 2022 09:16:58 GMT

And the distance between two nRF52 DK boards (master and slave) is about 20cm.

Meanwhile, I am using a nRF52 DK as the sniffer.

The setup is like the following picture:

RE: About the multiple ACKs in ATT MTU Throughput Example

EthanJia — Wed, 27 Apr 2022 08:03:51 GMT

OK. It is nRF52 DK

RE: About the multiple ACKs in ATT MTU Throughput Example

dejans — Wed, 27 Apr 2022 08:02:44 GMT

Hi,

Are you using DKs or custom boards?
Could you please provide more information about your setup?

Best regards,
Dejan

RE: About the multiple ACKs in ATT MTU Throughput Example

EthanJia — Wed, 27 Apr 2022 06:29:17 GMT

[quote userid="114127" url="~/f/nordic-q-a/87344/about-the-multiple-acks-in-att-mtu-throughput-example"]The screenshot of Wireshark[/quote]

Also, I think the wireshark record and corresponding csv files may help.

devzone.nordicsemi.com/.../1261.test2.pcapng devzone.nordicsemi.com/.../test2.csv

RE: About the multiple ACKs in ATT MTU Throughput Example

EthanJia — Wed, 27 Apr 2022 02:53:57 GMT

Forget to mention these parameters:

ATT MTU size: 247
Data length: 251
Connection Interval: 320 units (400ms)
Connection length extension: on
PHY: 2Mbps
GAP event length: 320 units (400ms)