ZyXEL Communications Prestige 316 User Manual page 153

Prestige 316 Broadband Sharing Gateway / Wireless LAN
PPTP Protocol Overview
PPTP is very similar to L2TP, since L2TP is based on both PPTP and L2F (Cisco's Layer 2 Forwarding).
Conceptually, there are three parties in PPTP, namely the PNS (PPTP Network Server), the PAC (PPTP
Access Concentrator) and the PPTP user. The PNS is the box that hosts both the PPP and the PPTP stacks
and forms one end of the PPTP tunnel. The PAC is the box that dials/answers the phone calls and relays the
PPP frames to the PNS. The PPTP user is not necessarily a PPP client; it can be a PPP server as well. Both
the PNS and the PAC must have IP connectivity; however, the PAC must in addition have dial-up
capability. The phone call is between the user and the PAC and the PAC tunnels the PPP frames to the PNS.
The PPTP user is unaware of the tunnel between the PAC and the PNS.
Diagram 4. PPTP Protocol Overview
Microsoft™ includes PPTP as a part of the Windows® O/S. In Microsoft™'s implementation, the PC and
hence the Prestige 316 is the PNS that requests the PAC (the ANT) to place an outgoing call over AAL5 to
an RFC-2364 server.
Control and PPP Connections
Each PPTP session has distinct control connection and PPP data connection.
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PPTP