**1. Introduction**

54 Mobile Networks

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The continuous development of wireless communication technologies yields diverse wireless networks that are widely deployed and successfully serviced according to their communication capabilities. Representative examples are cellular networks (e.g., cdma2000 and UMTS) capable of wide-area coverage and WLAN (Wireless LAN) efficiently used in public hot spots. WLAN and cellular network are complementary technologies. WLAN has several advantages over cellular networks, including higher data rate and lower operating and equipment costs. However, their coverage is typically limited to corporate buildings, residence, and certain public hot spots. On the other hand, cellular networks provide wide-area coverage but at lower speeds and much higher cost. It is indispensably required to integrate WLAN and cellular networks to serve users who need both high-speed wireless access as well as wide-area connectivity (Salkintzis, 2004).

Integrating heterogeneous networks reveals a lot of difficulties due to their different system specifications, standardization, and service scopes. For this reason, most of research work (3GPP, 2003; Ahmavaara et al., 2003; Buddhikot et al., 2003; Luo et al., 2003) are focused on interworking mechanism between network elements rather than integrating whole network architectures. Recently, with the intention of overcoming the limitation of existing wireless networks, new wireless communication service, WiBro is being deployed in Korea. WiBro is based on IEEE 802.16e (IEEE, 2001; Koffman & Roman, 2002) and is similar with Mobile WiMAX (Forum, n.d.). It is expected to provide enough mobility (60km/h) and higher data rate (50Mbps). So the study of the integration between WiBro and cdma2000 will give better effects than the existing works of the integration between WLAN and cdma2000.

In order to provide seamless services across heterogeneous wireless networks, efficient handoff procedure as well as flexible integrated network architecture is essentially required. As for handoff procedure, it is possible to use Mobile IP (Perkins, 2002) which is generally used in for homogeneous network or its extended version, so called low-latency handoff which tends to reduce packet loss and delay during the handoff (Maki, 2004). However, since these handoff procedures exploit L3 (layer 3) signaling messages, they have a problem that packet loss and delay can occur while processing L3 messages. In this paper, we propose an efficient L2 (layer 2) handoff scheme between cdma2000 and WiBro networks. The proposed L2 handoff scheme takes advantages over the existing L3 handoff scheme because it exploits L2 messages instead of L3 messages. We show the efficiency of our proposed L2 handoff through extensive computer simulations.

(a) Mobile IP (b) Low-latency handoff for Mobile IP

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,

A Fast Handover Scheme for WiBro and cdma2000 Networks 57

For wireless communication, mobile terminal performs step-by-step layered procedures. First, when it is initially booted or located in new wireless network area, it scans L1 signal. As soon as it detects L1 signal, it performs L2 connection procedure. After successful L2 connection, mobile terminal can communicate or send/receive packets. The L3 handoff described in Section 2 initiates handoff after L2 connection. Our proposed L2 handoff procedure exploits L2 signaling messages transmitted during L2 connection setup. By acquiring packet flow path between network elements (e.g. PDSN and ACR in Fig. 3) while processing L2 messages, our

The proposed L2 handoff procedure considers the interworking network architecture as shown in Fig. 3. The cdma2000 and WiBro networks are loosely-coupled integrated through interworking between PDSN of cdma2000 and ACR of Wibro. So in exception of interworking of PDSN and ACR, each network is working and servicing independently. Our L2 handoff

Fig. 2. L3 handoff procedure

2005) can be considered similarly.

**3. Proposed L2 handoff scheme**

method reduces packet loss occurred in handoff.

**3.1 Overview of L2 handoff**

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 4. Section 5 concludes the paper.
