TCP absolutely needs a heartbeat/keepalive to tell if the connection went down. There is no way to distinguish between no traffic being sent and session going d

TCP absolutely needs a heartbeat/keepalive to tell if the connection went down. There is no way to distinguish between no traffic being sent and session going down uncleanly. It's very common that some NAT drops the binding of an idle TCP connection and the peers don't discover that until their timeouts expire (could be anything from minutes to hours).