ZyXEL Communications ZyWALL 5 User Manual page 494

ZyWALL 5 Internet Security Appliance
Diagram I-2 PPTP Protocol Overview
Microsoft includes PPTP as a part of the Windows OS. In Microsoft's implementation, the PC, and
hence the ZyWALL, is the PNS that requests the PAC (the ANT) to place an outgoing call over AAL5
to an RFC 2364 server.
Control & PPP connections
Each PPTP session has distinct control connection and PPP data connection.
Call Connection
The control connection runs over TCP. Similar to L2TP, a tunnel control connection is first
established before call control messages can be exchanged. Please note that a tunnel control
connection supports multiple call sessions.
The following diagram depicts the message exchange of a successful call setup between a PC and an
ANT.
Diagram I-3 Example Message Exchange between PC and an ANT
PPP Data Connection
The PPP frames are tunneled between the PNS and PAC over GRE (General Routing Encapsulation,
RFC 1701, 1702). The individual calls within a tunnel are distinguished using the Call ID field in the
GRE header.
I-2 PPTP