3.9.2.3 KeepAlive Timer

HTTP Encapsulation protocols do not support a built-in KeepAlive timer, but instead rely on the encapsulated protocol to provide a KeepAlive mechanism. An encapsulated protocol SHOULD implement its own KeepAlive mechanism. The SSTP protocol provides its own KeepAlive mechanism (see [MS-GRVSSTP] section 2.2.13), using the SSTP_NOOP command<61>. The default client KeepAlive timeout value is 45 seconds. KeepAlive timers with short intervals SHOULD be used to maximize compatibility with a variety of firewalls and proxies. The KeepAlive timer event processing is handled as specified in section 3.9.6.3.