ZyXEL Communications ZyWall 10W User Manual page 607

ZyWALL Series Internet Security Gateway
Diagram L-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.
PPTP L-3