18.104.22.168 Hello Timer
To detect HTTPS connection failures in the absence of any active data transfers, Echo Request and Echo Response messages are periodically sent by the SSTP peer and SSTP far end, respectively. Both the SSTP client and SSTP server start a Hello timer after a successful SSTP connection setup. For example, after a successful Call Connect Request, Call Connect Acknowledge, and Call Connected message exchange, a Hello timer is initiated. The timer is restarted after receiving an SSTP packet (both the SSTP control packet and the SSTP data packet).
On expiry of the Hello timer, the SSTP peer MUST send an Echo Request packet. On receipt of Echo Request packet, the SSTP far end MUST respond with an Echo Response packet. If the SSTP far end does not respond with an Echo Response (or any SSTP packet) within the next timer interval, then it MUST abort the connection without sending a Call Abort packet.
The Hello timer SHOULD be set to 60 seconds.