Severe packet drop on Border Router with certain CoAP packet sizes

RE: Severe packet drop on Border Router with certain CoAP packet sizes

Robert Lubos — Thu, 22 Mar 2018 09:41:27 GMT

Hi,

I've been trying to reproduce the issue with current OpenThread master, but it either does not occur anymore or I wasn't able to trigger it.

My setup was RPi running current OpenThread border router on top of Raspbian, NCP connected through USB CDC-ACM and CLI application, both on nRF52840. On my RPi I've created CoAP server with our python CoAP implementation (https://github.com/NordicSemiconductor/piccata), CLI app was slightly modified to enable to send series of CoAP requests. I've sent mutliple series with different payload sizes, mostly near the size that caused packet fragmentation. Whatever payload size I've used, I had always got nearly 100% packet delivery.

In your description I was missing a single detail - have you been using Border Router shipped with our recent SDK (0.11.0) or OpenThread's Border Router? What was the CoAP server that you have used on RPi?

Anyway, we are going to release updated SDK with up-to-date libraries in the near future, so hopefully you could verify if the issue persists on your setup.

Best Regards,
Robert

RE: Severe packet drop on Border Router with certain CoAP packet sizes

Nopik — Wed, 07 Mar 2018 08:22:40 GMT

1) I was talking about CoAP payload, using code like this, values I referred to were `aDataLength`:

```

messagePtr = otCoapNewMessage(...);

otMessageAppend(messagePtr, aData, aDataLength); // aDataLength was variable here

otCoapSendRequest(...)

```

2) No, I didn't tried. The codebase I was using originally started from cli app, but had some deps added later on and it wasn't easy for me to try that code on a posix build.

3) I was using USB CDC-ACM mode. At the moment I don't have the setup for this on my desk, but later I will try to use UART as well.

4) Well, my understanding is that the root cause *is* in CoAP implementation (or border router/ncp), not related at all to nRF. Though until proved, that is only a hunch.

RE: Severe packet drop on Border Router with certain CoAP packet sizes

Lukasz Duda — Tue, 06 Mar 2018 19:47:50 GMT

Hello Nopik,

Thanks for detailed analysis. We will try to reproduce this issue on our side. I have couple questions though:

1) What do you mean by e.g. 90 bytes of payload - CoAP Payload, CoAP Payload + CoAP Header (including URIs) or size of 15.4 frame?

2) Did you try to reproduce this issue on posix simulator?

3) You mentioned on openthread-users forum that you use NCP over USB. Is it native USB or J-Link emulated UART over USB? If the first one, could you try reproduce the problem using UART? Although, i don't think that problem is located there.

4) Can you reproduce this issue using regular ICMP Echo Req/Rsp? If you see it only using CoAP, it would suggest that root cause may be located in CoAP implementation.

Regards,
Łukasz