Diagram 4 Pptp Protocol Overview - ZyXEL Communications Intelligent Broadband Sharing Gateway P-324 User Manual

When the Prestige is deployed in such a setup, it appears as a PC to the ANT (ADSL Network
Termination).
In Windows VPN or PPTP Pass-Through feature, the PPTP tunneling is created from Windows 95, 98 and
NT clients to an NT server in a remote location. The pass-through feature allows users on the network to
access a different remote server using the Prestige's Internet connection. In NAT mode, the Prestige is able
to pass the PPTP packets to the internal PPTP server (i.e. NT server) behind the NAT. Users need to
forward PPTP packets to port 1723 by configuring the server in Menu 15.2 - Server Set Setup. In the case
above as the PPTP connection is initialized by the remote PPTP Client, the user must configure the PPTP
clients. The Prestige initializes the PPTP connection hence, there is no need to configure the remote PPTP
clients.
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 (can be a PPP server too). 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 OS. In Microsoft's implementation, the PC, and hence
the Prestige, is the PNS that requests the PAC (the ANT) to place an outgoing call over AAL5 to an RFC
2364 server.
Control & PPP connections
PPTP 5