2 posts / 0 new
Last post
rchoubey
Clarify Maxium CoAP packet sizes

Please clarify for below request,

   1) the maximum request packet size     2) the maximum response packet size

The HDLC layer to the device has a message size of 512, leaving a maximum of payload of 512 - 7 (HLDC header size).

However, if I attempt to send a 286 byte request to the end point I get a 4.13 request entity too large. 158 byte requests work. So what is the actual limit for a request (presumably somewhere between 158 and 286)? I know previously (I haven't checked this on the new network) the request to the device contained the uri-host option e.g, coap://SSN001350050044FCD8.sg.yel01.ssn.ssnsgs.net which is a waste of bytes (uri host has no meaning to the client anyway). It would be great if I could get a 286 byte packet through somehow, e.g. by not sending the uri-host to the client...

For responses, we have a hard coded limit of 230 bytes for responses from trial and error, what should it be set to? again increasing this to 286 would be great.

BTW the reason 286 is important is that it is the size of a 256 byte CoAP block transfer with header, if we don't get to 286 then we are limited to 128 byte block transfers. We use block transfers to load firmware onto our device, which works @ 128 bytes but it would be nice to double the speed by getting 256 byte blocks.

rchoubey
Re:Clarify Maxium CoAP packet sizes

We are almost sure about the maximum payload being 256 bytes ( including some bytes for header), but we are in touch with our engineering team to get a confirmation on the same.

You may have to break down msgs which are of size more than 256 ( including header).