Client using WizFi310 chip TCP session and retransmissions causing firmware download failure

I am working at the wireless escalation team with Cisco Systems.
We have a customer who has raised issue that their device using WizFi310 chip is failing to complete firmware download from the server in internet.

We are using one of their devices to test in Cisco lab and found difference in the working on the TCP transactions. We would like to get those questions clarified to further troubleshoot the issue from Cisco perspective.

  1. In many occasions the client is sending TCP re-transmission though it has already sent ACK to the server.

  2. Sometimes the client is not doing ACK for a long time (sometimes for upto 7seconds) during this time the server is doing a TCP re-transmission. We tested the same with a windows client and this behavior is not seen when the same file is downloaded from the same server.

Few other questions as well needs clarification.

We have packet captures to substantiate these issues.
It would be great if you can please let me know how to proceed with this debugging. We can setup joint debugging in our lab if required.

Sudhagar Singh
Wireless Escalation, Cisco Systems.