**2. Handoff in heterogeneous wireless networks**

Since the integration of widely deployed 3G cdma2000 and WLAN can give a lot of benefits to both end users and service providers, there has been a lot of researches about interworking mechanism between cdma2000 and WLAN (3GPP, 2003; Ahmavaara et al., 2003; Buddhikot et al., 2003; Luo et al., 2003; Salkintzis, 2004). The WLAN and 3G cdma2000 integration architecture is characterized by the amount of interdependence it introduces between the two component networks. Two candidate integration architectures, tightly-coupled and loosely-coupled interworking are described in Fig. 1.

Fig. 1. Interworking architecture of heterogeneous wireless networks

In the tightly-coupled interworking approach, WLAN networks appear to 3G core network as another 3G RAN (Radio Access Network). The WLAN gateway hides the details of the WLAN network to the 3G core network, and implements all the 3G protocols. Even though this approach can share the same authentication, signaling, and billing infrastructures, independent from physical layer interface, it has a disadvantage that the capacity and configuration of each network element is carefully reengineered and can result in high cost. On the contrary, the loosely-coupled interworking approach has several advantages such that 3G networks and WLAN can be independently deployed without extensive capital investments and its implementation is relatively easy. Therefore, it has emerged as a preferred

Fig. 2. L3 handoff procedure

2 Mobile Networks

The paper is organized as follows: Section 2 summarizes existing techniques for handoff scheme as related work. Section 3 presents the proposed L2 handoff scheme and we describe the performance characteristics of the proposed scheme through OPNET simulation in Section

Since the integration of widely deployed 3G cdma2000 and WLAN can give a lot of benefits to both end users and service providers, there has been a lot of researches about interworking mechanism between cdma2000 and WLAN (3GPP, 2003; Ahmavaara et al., 2003; Buddhikot et al., 2003; Luo et al., 2003; Salkintzis, 2004). The WLAN and 3G cdma2000 integration architecture is characterized by the amount of interdependence it introduces between the two component networks. Two candidate integration architectures, tightly-coupled and

4. Section 5 concludes the paper.

**2. Handoff in heterogeneous wireless networks**

loosely-coupled interworking are described in Fig. 1.

Fig. 1. Interworking architecture of heterogeneous wireless networks

In the tightly-coupled interworking approach, WLAN networks appear to 3G core network as another 3G RAN (Radio Access Network). The WLAN gateway hides the details of the WLAN network to the 3G core network, and implements all the 3G protocols. Even though this approach can share the same authentication, signaling, and billing infrastructures, independent from physical layer interface, it has a disadvantage that the capacity and configuration of each network element is carefully reengineered and can result in high cost. On the contrary, the loosely-coupled interworking approach has several advantages such that 3G networks and WLAN can be independently deployed without extensive capital investments and its implementation is relatively easy. Therefore, it has emerged as a preferred architecture for the integration of WLAN and 3G networks. As previously mentioned, the L3 handoff procedure is commonly used to provide mobility services in the loosely coupled interworking architecture. Mobile IP is the representative technology of L3 handoff to provide mobility services within homogeneous 3G cdma2000 or between 3G cdma2000 and WLAN. When mobile station moves into new wireless network, Mobile IP performs registration procedure and handoff are completed after registration procedure as shown in Fig. 2(a). The low-latency handoff for Mobile IP (Maki, 2004) is proposed to reduce packet loss occurred in the registration procedure. It reduces packet loss by providing tunneling and buffering between the previous and new networks as depicted in Fig. 2(b). Since the current cdma2000 networks employ Mobile IPv4, we deal with Mobile IPv4 and its extended version in this paper. So the low latency handoff for Mobile IPv4 in Fig. 2(b) will be used in performance evaluation of Section 4. In IPv6 environment, however, fast handoff for Mobile IPv6 (Koodli, 2005) can be considered similarly.
