The user plane for the PDP type PPP consists of a PPP protocol stack above SNDCP for A/Gb mode or above PDCP for Iu mode in the MS, and above GTP in the GGSN. The GGSN may either terminate the PPP protocol and access the packet data network at the IP level, or further tunnel PPP PDUs via e.g. L2TP.
In case the application above PPP uses a different protocol than IP (e.g. IPX or AppleTalk), the interconnection to the packet data network is outside the scope of this specification.