One of the principal objectives of interworking is to allow independent evolution of 3GPP (WWAN) and WLAN standards. The extent of interdependence between these standards should be minimized or localized at the point of interconnection.
Support for the legacy WLAN user is perhaps the most important objective of a 3GPP-WLAN interworking setup. A legacy WLAN user is a user with a WLAN-capable device and a subscription to 3GPP services. The user may or may not be 3GPP capable. Such a user should be able to access 3GPP services without substantial hardware/software upgrades. Such a setup would result in a strong business case, leading to extend the facility of 3GPP services to the user who, although having a 3GPP subscription, does not want to spend it on additional hardware/software upgrades. The other objective of interworking is the single subscription.
The following are the interworking requirements:
Common billing and customer care. This is the simplest form of interworking that provides a common bill and customer care to the subscriber but otherwise requires no real interworking between the WLAN and 3GPP data networks.
3GPP-based access control and charging. This requires authentication, authorization, and accounting (AAA) for subscribers in the WLAN to be based on the same AAA procedures used in the 3GPP data networks. It means a mobile subscriber can use his or her subscriber identity module/ UMTS-SIM (SIM/USIM) to access WLAN services.
Access to 3GPP-based packet switched services. The aim of this requirement is to allow the mobile operator to allow access to its 3GPP data services to subscribers in a WLAN environment. It means a mobile subscriber should be able to access/select 3GPP data services through the WLAN access network. Although the user is allowed access to the same 3GPP data services over both the 3GPP and WLAN access networks, no service continuity across these access networks is required in this scenario.
Service continuity. The goal is to allow seamless service continuity across the 3GPP and WLAN systems. It means that a user session during mobility across these networks should not only continue but also should not have noticeable service change in terms of quality and disruption.
Access to 3GPP circuit-switched services. The goal of this requirement is to allow the 3GPP operator to offer access to circuit-switched services such as voice calls from the WLAN systems. Seamless service continuity is a must for these services.
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