ZyXEL Communications Broadband Security Gateway P-312, User Manual, Page: 229 / 254

P312 Broadband Security Gateway
PPTP H
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.
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
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.
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.