I'm interested in TCP connection between mobile unit which is connected over GPRS to server on public network. I need to keep open, so I will send periodically keep-alive packets for hold session. Trouble is, that I must have a long-term period of sending keepalive packets for minimal data traffic, but I need to get to know that session is broken as fast as possible. How I tested on a few operators, NAT boxes don't send any information, such as TCP-RST or any ICMP message, that mapping is cancelled.
Could anyone advise me how could mobile unit get to know that session is broken?
Thank you very much