Section: 12.2 PDN Interworking Model
Content: The interworking point is at the Gi reference point. The GGSN for interworking with the ISP/PDN is the access point of the Packet Domain (see figure 13). The GGSN will either terminate the PPP connection towards the MS or may further relay PPP frames to the PDN. The PPP frames may be tunnelled in e.g. L2TP. Figure 13: The protocol stacks for the Gi PPP reference point In case the external PDN is an IP based network and the GGSN terminates PPP the same description applies as specified in subclause 11.2. In case the GGSN tunnels PPP frames to the PDN, the GGSN may behave like a LAC towards the external network.