Recent development on the wireless networks has indicated that IEEE 802.11.x standards based wireless LAN and third-generation cellular wireless networks such as CDMA2000 or UMTS (i.e., WCDMA) could be integrated together to offer ubiquitous Internet access to end users. The two technologies can offer functions that are complementary to each other. The 802.11. x standards based wireless LANs support data rates from 1 Mbps to 54 Mbps. However, by IEEE 802.11.x standard, one access point (AP) can only cover an area of a few thousand square meters. It is perfectly applied for enterprise networks and public hot-spots such as hotels and airports. On the contrary, wireless cellular networks built with 3G standards can only support peak data transmission rates from 64Kbps to nearly 2 Mbps with a much wider area. It is reasonable and feasible to combine these two technologies to make Internet access much easier and more convenient. The design of an interworking architecture to efficiently integrate 3G cellular wireless networks and 802.11.x standard based wireless LANs is a challenge. Its difficulty lies in the objective of the integration, which is to achieve the seamless interoperation between the two types of the wireless networks with certain QoS guarantee and other requirements kept simultaneously, from the perspectives of both the end-users and the operators. There are basically two proposals as the solutions to the architecture of the integration. One is the tight coupling. The other is the loose coupling. Although there is no final selection on whether the future integrated network would use either of these techniques or another one, much focus of the research is on the loose coupling due to its feasibility. To implement the integration based on the corresponding approach, there are a lot of issues needed to be addressed. They are the mobility management for vertical handoff, the QoS maintenance during the vertical handoff, and the schemes of authentication, authorization and the accounting (AAA). In this article, we will focus on the issue of interworking architecture. The rest of the text is organized as follows. The second section will present the general ideas on the architecture of the integration of 3G cellular networks with wireless LANs. The third section will present several proposals on the architectures of the integration. At last, the fourth section will conclude the article.
The Framework Of Interworking Architecture
The first important thing in the integration of 3G and wireless LAN is the development of concept architecture for 3G cellular and wireless LAN networks. This architecture should be able to support any type of user services in a secure and auditable way. Both user interfaces and interoperator interfaces must be clearly defined. And multiple service providers should be able to interoperate under the guidelines of this architecture. The users could choose the best available connection for the applications they are using at the active time.
Several approaches have been proposed for interworking networks architecture. The European Telecommunications Standards Institute (ETSI) specifies two generic approaches for interworking: loose-coupling and tight-coupling (Buddhikot, Chandranmenon, Han, Lee, Miller, & Salgarelli, 2003; Findlay, Flygare, Hancock, Haslestad, Hepworth, & McCann, 2002). The two candidate integration architectures are characterized by the amount of interdependence they introduce between the two component networks. On the other hand, the Third Generation Partnership Project (3GPP) (Ahmavaara, Haverinen, & Pichna, 2003; Salkintzis, 2004) has specified six interworking scenarios. The six interworking scenarios provide a general and detailed picture on the transition from the loose-coupling to the tight-coupling interworking architecture.