3.1.6.3 KeepAlive Timer Event

A KeepAlive Timer Event SHOULD trigger an encapsulated protocol message such as an SSTP_NOOP command to be sent across the wire by LongLived Client implementations<14>. Well behaved connections will see this event every KeepAlive timer interval when the session is idle. After firing, the KeepAlive timer SHOULD be restarted.