In computer networking, Secure Socket Tunneling Protocol (SSTP) is a form of virtual private network (VPN) tunnel that provides a mechanism to transport Point-to-Point Protocol (PPP) traffic through an SSL/TLS channel.
It is fully integrated with the RRAS architecture in these operating systems, allowing its use with Winlogon or smart-card authentication, remote-access policies and the Windows VPN client.
[5] SSTP is intended only for remote client access, it generally does not support site-to-site VPN tunnels.
In general, performance will be acceptable only as long as there is sufficient excess bandwidth on the un-tunneled network link to guarantee that the tunneled TCP timers do not expire.
If this becomes untrue, performance falls off dramatically due to the TCP meltdown problem.