An SSTP VPN (from Microsoft) is a form of SSL VPN.
"Secure Socket Tunneling Protocol (SSTP) is a form of VPN tunnel that provides a mechanism to transport PPP or L2TP traffic <b>through an SSL 3.0 channel</b>..."
Last Wiki Answer Submitted: May 17, 2013 7:34 pm by Michael Tidmarsh11,380 pts.
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The reason you would likely use SSTP over previous SSL versions is because you are using Windows 2008 RRAS, where it is implemented already.
A good discussion can be found here:
http://biztechmagazine.com/article.asp?item_id=377