CC3220MODA: Send successively many keep-alive packets for 10seconds

Hello,

My program sends 24KB TCP packet every 0.16s to the gateway PC.
During the transmission, TCP connection did disconnect suddenly.

I attach the packet capture result at that time.
This file captured only received packet at the gateway server PC.
Unfortunatelly, transmission packets from PC were not captured.

CC3220MOD's IP port (src) is 57762.
Gateway PC's IP port (dest) is 5001.

Until packet 2777, TX OK.
From packet 2790, CC3220MOD sent successively many keep-alive packets for 10seconds.
After that, my program had receive error "-1" from sl_Send(), then closed socket by sl_Close().

Are these keep-alive packets expected behaviour?

Condition: CC3220MODASF, SDK 2.10.00.04

Regards,
Nobuhiro