Simple IP with VPN

An enhancement to simple IP is the capability to introduce a VPN to the
path for security and also to provide connectivity to a corporate LAN or
other packet networks.With VPN, the mobile user should have the appearance
of being connected directly to the corporate LAN.
The PDSN establishes a tunnel using the Layer Two Tunneling Protocol
(L2TP) between the PDSN and the private data network. The mobile is
effectively still using a PPP connection, but it is tunneled. The private network
that the PDSN terminates to is responsible for assigning the IP
address and, of course, authenticating the user beyond what the wireless
system needs to perform for billing purposes.
Because of the specific termination and authentication that is performed
by another network, the PDSN does not apply any IP services for the mobile
and except for the predetermined speed of the connection that is all the system
can provide.

Just as in the case of Simple IP, the mobile must still be connected to the
same PDSN for the packet session. If the mobile moves to another area of
the network, which is covered by a separate PDSN, the VPN is terminated
and the mobile must reestablish the session. A simplified diagram is shown
in Figure 7-13.
The packet session flowchart for Simple IP with VPN is shown in Figure
7-14 and assumes the subscriber is not ROAMing. 305