Abstract With the rapid growth of mobile Internet, offering seamless connectivity in different types of wireless networks is an important feature in next generation wireless networks (4G networks). Mobile IP (MIP) is expected to play a key role to handle the movements of mobile nodes (MNs) in 4G networks. However, MIP suffers from long handoff latency since it is designed to support the macromobility of a MN. Therefore, it is necessary to devise a scheme that provides currently deployed networks with backward compatibility and that offers seamless connectivity during MIP handoffs across the heterogeneous wireless networks. In this paper, we propose a client‐based vertical handoff system for multi‐networks to provide end‐users with seamless connectivity across heterogeneous wireless networks. Our proposed system is designed as a common network interface at a client side and provides transparent service to IP/MIP layers regardless of used wireless technologies. With this system, we also present vertical handoff performance over a loosely coupled cdma2000/WLAN experimental test‐bed. The experimental results show that our system enables a MN to handoff seamlessly across different types of wireless networks without any modifications to the existing IP/MIP stack and core network. Copyright © 2008 John Wiley & Sons, Ltd.

With the rapid growth of mobile Internet, offering seamless connectivity and high-speed multimedia services in different types of wireless networks are important features in next generation wireless networks (4G networks). Many researchers envision that the 4G networks will consist of many radio access technologies which integrate into all IP-based networks while providing seamless handoffs across the heterogeneous wireless networks. Mobile IP is a prominent solution to handle mobile nodespsila movement in IP-based networks. However, Mobile IP suffers from long handoff latency since it is designed to support the macromobility of a mobile node. Therefore, it is necessary to devise a scheme that offers seamless connectivity during Mobile IP handoffs across the heterogeneous wireless networks. In this paper, we propose a client-based handoff management system for multi-networks to provide end-users with seamless connectivity across heterogeneous wireless networks. Our proposed system is designed as a common network interface at a client side and provides transparent services to IP/MIP layers regardless of used wireless technologies. With this system, we also present vertical handoff performance over a loosely coupled cdma2000/WLAN experimental test-bed. The experimental results show that our system enables a mobile node to handoff seamlessly across different types of wireless networks without any modifications to the existing IP/MIP stack and core network.

The IEEE 802.16e system supporting mobility on fixed wireless-MAN systems is supposed to be a mobile broadband wireless access (BWA) and evolve into 4G mobile communication systems. Although the system already defines its own mobility management algorithm, a network layer handover algorithm should be defined to support the mobility of mobile stations in the Internet. There are many active researches on how to apply the L3 handover protocol over the existing IEEE 802.16e L2 handover scheme, but most of the previous works have focused on the timing of L3 handover messages over the IEEE 802.16e L2 handover messages. In this paper, we propose a new handover scheme for fast mobile IPv6 over the IEEE 802.16e system. By integrating FMIPv6 with IEEE 802.16e system efficiently, the proposed scheme can minimize not only L3 handover latency but also packet losses.

Mobile IPv6, which is a protocol being standardized by IETF for global IP mobility support, is expected to play a key role for future all-IP wireless networks. As the demands for delay sensitive real-time applications increase, the handover latency of mobile IPv6 becomes inadequate for these applications. There have been many proposals, such as fast handovers for mobile IPv6 (FMIPv6), to tackle this problem. However, FMIPv6 only concentrates on the protocol operation while it does not address other issues, such as radio access discovery and candidate access router discovery, that are critical to the handover performance of FMIPv6. Therefore, in this paper, we propose ARIP (access router information protocol), which performs a candidate access router discovery and a radio access network discovery in one protocol suite, to provide an efficient handover framework for MIPv6 and FMIPv6. ARIP is designed to cope with heterogeneous networks as well as homogeneous networks and to be closely coupled with FMIPv6 to provide an efficient handover operation. The performance evaluation of MIPv6, FMIPv6, and FMIPv6 with ARIP is performed in an actual network environment and the performance results show that FMIPv6 with ARIP gives the best performance in terms of handover latency

There has been much research effort to exploit the multi-rate capability of WLANs to improve performance. While these approaches focused on exploiting good channel conditions for direct transmission between stations, there are no considerations of performance degradation by low rate transmissions due to poor channel conditions. Thus, we propose a frame relay based MAC protocol, termed FR-MAC, to tackle this issue and to improve network performance. The key idea of FR-MAC is that the time required to transmit a frame using an intermediate station as a relay can be much smaller than the direct transmission at a lower rate, if the intermediate station between the source and the receiver can relay the frame at higher rates. Simulation results show that the proposed protocol improves network performance and the amount of improvement significantly increases as the number of relayed stations and the payload size are increased.

Recently, many on-demand routing protocols for ad-hoc networks have been proposed, but most of these works have been done on the basis of the IEEE 802.11 standard that supports a single transmission rate. In ad hoc networks supporting the multi-rate transmission scheme, which is referred to as dynamic rate shifting in the IEEE 802.11 standard, few performance studies on ad-hoc routing protocols have been performed. In this paper, we extensively study the impact of dynamic rate shifting on the performance of ad-hoc routing protocols in various situations in multi-rate WLANs environments. Our question is whether the dynamic rate shifting scheme supported by the IEEE 802.11 standard affects the relative performance of the routing protocols being studied. We have extended the ns-2 network simulator to accurately model the IEEE 802.11b wireless LAN standard, and simulated the performance of two ad hoc routing protocols over each of networks supporting single rate and multi-rate transmissions.

In this paper, we propose an efficient multicast routing protocol based on mobile IP standard in wireless mobile networks. A mobile host that is located in a foreign network receives a tunneled multicast datagram from a multicast agent, which is located in a remote network or local network. While receiving a tunneled multicast datagram from a remote multicast agent, the local multicast agent starts a multicast tree join operation if the mobile host is expected to remain the network relatively long period of time, while it does not start multicast tree join operation if the mobile host is expected to remain the network relatively short period of time. The proposed protocol tries to maximize the number of unnecessary multicast tree join operations. We examined performance of the proposed protocol by simulation under various environments and we got good performance results.

The routing protocols designed for wired networks can hardly be used for mobile ad-hoc networks due to unpredictable topology changes, and thus several routing protocols for mobile ad-hoc networks have been proposed. The goal of this paper is to select the most reliable route that is impervious to failures by topological changes by mobile nodes' mobility. To select a reliable route, we introduce the concept of stable zone and caution zone, and then apply it to the route discovery procedure of the existing on-demand routing protocol (i.e. AODV). The concept of the stable zone and caution zone, which are located in a mobile node's transmission range, is based on a mobile node's location and mobility information received by Global Positioning System (GPS). The proposed protocol was evaluated by simulation in various conditions and we got an improved performance.

Providing multicast service to mobile hosts is difficult due to frequent changes of mobile host location and group membership. To overcome the difficulty, several multicast protocols for mobile hosts have been proposed. Although the protocols solve several problems inherent in multicast routing proposals for static hosts, they still have problems such as non-optimal delivery path, datagram duplication, etc. In this paper, we summarize these problems of multicast routing protocols and propose an efficient multicast protocol using a multicast agent in wireless mobile networks, where a mobile host receives a tunneled multicast datagram from a multicast agent located in a network close to it or directly from the multicast router in the current network. While receiving a tunneled multicast datagram from a remote multicast agent, the local multicast agent starts multicast join process, which makes the multicast delivery route optimal. The proposed protocol reduces data delivery path length and decreases not only the amount of duplicate copies of multicast datagrams but also multicast traffic load. We examined and compared the performance of the proposed protocol and existing protocols by simulation under various environments and we got an improved performance over the existing proposals.