24.3273GPPGeneral Packet Radio System (GPRS) and 3GPP I-WLAN aspectsMobility between 3GPP Wireless Local Area Network (WLAN) interworking (I-WLAN) and 3GPP systemsRelease 12Stage 3TS
In order to act as home link, the system can have the HA function collocated.
For instance, the GPRS system can be the UE home link if the GGSN function and the HA function are logically collocated. The UE receives HNP when attaching to GPRS. In this case, the interface between GGSN and HA function becomes an internal interface.
When the GGSN (or PDG) and the HA function are collocated, it is assumed that some information (e.g. UE binding information) and the network resource (e.g. IP address pool) are shared. Some kind of signalling between the two functions is necessary. How the information and resource are shared between the two functions is an implementation issue, which is out of the scope of this TS.