well as lized services such as e-mail, online augmented by wireless networks that support mobility for shopping and banking, ticket reservations, and restaurant end users. advice. In spring 2001, DoCoMo introduced its next generation mobile system, based on wideband CDMA 6. 1. wireless local area networks W-CDMA), which can support speeds of 384Kbps or faster, allowing users to download video images and other Devices used in wireless local area network (WLAN bandwidth-intensive content with its high-speed packet technologies are light-weight(easy to carry)and flexible data communications in network configuration. Therefore, WLANS are suitable for office networks, home networks, personal area 5.2. Implementation networks(PANS), and ad hoc networks. In a one-hop WLAN environment, where an access point(AP)acting as In a wireless environment, IP and TCP require a router or switch is a part of a wired network, mobile significant modification in order to adapt to features like devices connect directly to the AP through radio channels nobility and radio communication Data packets are relayed by an AP to the other end of a Mobile IP. The Mobile IP [ 6] defines enhancements network connection. If no APs are available, mobile that permit Internet Protocol (IP)nodes(hosts and routers) devices can form a wireless ad hoc network amon using either IPv4 or IPv6 to seamlessly"roam"among IP themselves and exchange data packets or perform business subnetworks and media types. It supports transparency transactions as necessary above the IP layer, including the maintenance of active In Table 4, major WLan technologies are compared TCP connections and UDP port bindings. Two types of in terms of maximum data transfer rate(channel mobile-IP capable router, home agent (HA)and foreign bandwidth), typical transmission range, modulation agent(FA), are defined to assist routing when the mobile techniques, and operational frequency bands. The various node is away from its home network. All datagrams combinations of modulation schemes and frequency bands destined for the mobile node are intercepted by Ha and make up different standards, which result in different tunneled to FA. FA then delivers these packets to the throughputs and coverage ranges mobile node through a care-of-address established when the mobile node is attached to Fa TCP for mobile networks. Transmission Control Modulation/ Standard Data Range(m) Protocol (TCP) was designed for reliable data transport on Rate wired networks and its parameters have been fine-tuned M Band (ghz) for such environments. As a result, when it is applied Bluetooth 5-10 GFSK/2.4 directly to mobile networks, TCP performs poorly due to 80211b 154 HR-DSSS /2.4 factors such as error-prone wireless channels, fre handoffs and disconnections. In order to optimize reliable 802\%N2 0-100OFDM/5 have been proposed for mobile networks. Yavatkar and L8onig2 data transport performance, a number of variants of TCP 50-300 OFDM/5 0-150 OFDM /2.4 Bhagawat [16] proposed an approach that splits the path Table 4. Major WLAN standards between the mobile node and the fixed node into two separate sub-paths: one over the wireless links and the other over the wired links. This approach limits the TCP In general, Bluetooth technology supports very performance degradation in a"short" wireless link limited coverage range and throughput. Thus it is only connection. Balakrishnan et al. [1] proposed a"packet suitable for applications in personal area networks. In caching scheme to reduce the TCP retransmission many parts of the world, the IEEE 802.11b(Wi-Fi)system is now the most popular wireless network and is used in overhead due to handoff. The scheme proposed in [21 offices, homes, and public spaces such as airports, utilizes the fast retransmission option immediately after shopping malls, and restaurants. However, many experts handoff is completed and shows smooth TCP performance during handoff predict that with much higher transmission speeds 802. 1la and 802.11g will replace 802. 1lb in the near future 6. Wireless Networks 6.2. Wireless wide area networks Network infrastructure provides essential voice and data communication capability for consumers and vendors Originally designed for voice-only communication, in cyberspace. Evolving from electronic commerce (EC) cellular systems are evolving from analog to digital,and to mobile commerce (MC), it is necessary for a wired from circuit-switched network infrastructure. such as the Internet. to be order to accommodate mobile commerce (data) Proceedings of the 23 rd International Conference on Distributed Computing Systems Workshops(ICDCSw03 SOCIETY 0-7695-1921-003$1700@2003lEEEwell as specialized services such as e-mail, online shopping and banking, ticket reservations, and restaurant advice. In spring 2001, DoCoMo introduced its next￾generation mobile system, based on wideband CDMA (W-CDMA), which can support speeds of 384Kbps or faster, allowing users to download video images and other bandwidth-intensive content with its high-speed packet data communications. 5.2. Implementation In a wireless environment, IP and TCP require significant modification in order to adapt to features like mobility and radio communication. Mobile IP. The Mobile IP [6] defines enhancements that permit Internet Protocol (IP) nodes (hosts and routers) using either IPv4 or IPv6 to seamlessly “roam” among IP subnetworks and media types. It supports transparency above the IP layer, including the maintenance of active TCP connections and UDP port bindings. Two types of mobile-IP capable router, home agent (HA) and foreign agent (FA), are defined to assist routing when the mobile node is away from its home network. All datagrams destined for the mobile node are intercepted by HA and tunneled to FA. FA then delivers these packets to the mobile node through a care-of-address established when the mobile node is attached to FA. TCP for mobile networks. Transmission Control Protocol (TCP) was designed for reliable data transport on wired networks and its parameters have been fine-tuned for such environments. As a result, when it is applied directly to mobile networks, TCP performs poorly due to factors such as error-prone wireless channels, frequent handoffs and disconnections. In order to optimize reliable data transport performance, a number of variants of TCP have been proposed for mobile networks. Yavatkar and Bhagawat [16] proposed an approach that splits the path between the mobile node and the fixed node into two separate sub-paths: one over the wireless links and the other over the wired links. This approach limits the TCP performance degradation in a “short” wireless link connection. Balakrishnan et al. [1] proposed a “packet caching” scheme to reduce the TCP retransmission overhead due to handoff. The scheme proposed in [2] utilizes the fast retransmission option immediately after handoff is completed and shows smooth TCP performance during handoff. 6. Wireless Networks Network infrastructure provides essential voice and data communication capability for consumers and vendors in cyberspace. Evolving from electronic commerce (EC) to mobile commerce (MC), it is necessary for a wired network infrastructure, such as the Internet, to be augmented by wireless networks that support mobility for end users. 6.1. Wireless local area networks Devices used in wireless local area network (WLAN) technologies are light-weight (easy to carry) and flexible in network configuration. Therefore, WLANs are suitable for office networks, home networks, personal area networks (PANs), and ad hoc networks. In a one-hop WLAN environment, where an access point (AP) acting as a router or switch is a part of a wired network, mobile devices connect directly to the AP through radio channels. Data packets are relayed by an AP to the other end of a network connection. If no APs are available, mobile devices can form a wireless ad hoc network among themselves and exchange data packets or perform business transactions as necessary. In Table 4, major WLAN technologies are compared in terms of maximum data transfer rate (channel bandwidth), typical transmission range, modulation techniques, and operational frequency bands. The various combinations of modulation schemes and frequency bands make up different standards, which result in different throughputs and coverage ranges. Standard Max. Data Rate (Mbps) Typical Range (m) Modulation/ Frequency Band (GHz) Bluetooth 1 5 – 10 GFSK / 2.4 802.11b (Wi-Fi) 11 50 – 100 HR-DSSS / 2.4 802.11a 54 50 – 100 OFDM / 5 HyperLAN2 54 50 – 300 OFDM / 5 802.11g 54 50 – 150 OFDM / 2.4 Table 4. Major WLAN standards In general, Bluetooth technology supports very limited coverage range and throughput. Thus it is only suitable for applications in personal area networks. In many parts of the world, the IEEE 802.11b (Wi-Fi) system is now the most popular wireless network and is used in offices, homes, and public spaces such as airports, shopping malls, and restaurants. However, many experts predict that with much higher transmission speeds, 802.11a and 802.11g will replace 802.11b in the near future. 6.2. Wireless wide area networks Originally designed for voice-only communication, cellular systems are evolving from analog to digital, and from circuit-switched to packet-switched networks, in order to accommodate mobile commerce (data) Proceedings of the 23 rd International Conference on Distributed Computing Systems Workshops (ICDCSW’03) 0-7695-1921-0/03 $17.00 © 2003 IEEE