MTU size determination on N36

Questions & Answers
1

General Information

  • Product: e.g. N46-801-16-BL
  • Serial Number:
  • Ensenso SDK Version: 3.5.1394
  • Operating System: Linux

Problem / Question

Just upgraded from a N35 camera to a N36 camera and now we have problems with the MTU size. SDK version 3.5.1394 added the MTU node inside the config jsons. How/when does this MTU size get determined? During calibration? Because currently it is stuck at 1500 and giving the low MTU size warning. The NIC of the connected pc does have the MTU set to 9000 and the correctly sized ring buffers.

Thanks in advance!

2

Hi,

for GigE Vision based cameras the MTU is negotiated by sending packets of different sizes and checking whether they arrive. See this article for some general information.

This means that all network devices on the path from PC to camera have to support jumbo frames. If any of them doesn’t, larger packets will get stuck at it.

All of our cameras support jumbo frames out of the box. If you already enabled them on your PC, there is probably some switch which doesn’t support them or is not configured to use them yet.

3

Thanks for the information. I had my suspicions that the switch was the problem.

As a small follow-up: when does this negotiating happen? At every startup of the camera or sometime else?

4

Hi Koen

yes, switches will most likely need configuration before allowing jumbo packets to pass without fragmentation.

The MTU negotiation happens during cmdOpen when setting up the communication ports.

best regards
Rainer

5

Oh btw, my answer wasn’t completely accurate: the packets have the ‘dont fragment’ flag set. So if any equipment cannot handle them, they will be dropped instead of fragmented.