1 | initial version |
This capture confirms what you already know: the communication stops somewhere between frame 76 (last TCP-ACK) and frame 80 (first retransmission).
The capture was done at the server side, so when there is no more incoming traffic you still don't know the cause. It could be the 'end device' or something went wrong in the path between the end device and server. For instance a routing problem or a firewall that dropped the session after a timeout.
To know for sure you need to (also) capture the traffic at the end device side, or as close as possible. Capture continuously (use a ring-buffer) and stop the capture when the issue occurred at this device. The best way to convince the supplier is to use a tap.
With a capture at the end device side you can check if the retransmissions form the server do arrive and if the end device really stops responding or if the send packets were dropped in the network.