Essential Mobile-Commerce Technology (part 1) - WIRELESS NETWORKS

3/12/2013 7:08:01 PM


Without ways to conduct secure commercial information exchange and safe electronic financial transactions over mobile networks, neither service providers nor potential customers will trust mobile commerce. Various mobile security procedures and payment methods have been proposed and applied to mobile commerce. A secure mobile commerce system must have the following properties: (i) confidentiality, (ii) authentication, (iii) integrity, (iv) authorization, (v) availability, and (vi) non-repudiation. A discussion of the security issues related to the three network paradigms, wireless local area networks, wireless wide area networks, and WAP, is also included. Among the many themes of mobile commerce security, mobile payment methods are probably the most important. A typical mobile payment process includes: (i) registration, (ii) payment submission, (iii) authentication and authorization by a content provider, and (iv) confirmation.


Network infrastructure provides essential voice and data communication capability for consumers and vendors in cyberspace. As part of the evolution from electronic commerce (EC) to mobile commerce (MC), it is necessary for the existing wired network infrastructure, i.e. the Internet, to be augmented by a series of wireless networks that support mobility for end users. Wireless networking technologies are advancing at a tremendous pace and each represents a solution for a certain phase, whether 1G, 2G, and 3G, in a particular geographical area such as the United States, Europe, or Japan. In this section, they will be categorized in terms of their radio coverage as wireless local area networks, wireless metropolitan area networks, or wireless wide area networks.

Mobile Middleware

The term middleware refers to the software layer that lies between the operating system and the distributed applications that interact via the networks. The primary mission of a middleware layer is to hide the underlying networked environment's complexity by insulating applications from explicit protocols designed to handle disjoint memories, data replication, network faults, and parallelism . Mobile middleware translates requests from mobile stations to a host computer and adapts content from the host to the mobile station (Saha, Jamtgaard, & Villasenor, 2001).

WAP and i-mode

According to an article "Frequently asked questions about NTT-DoCoMo's i-mode" (Eurotechnology Japan K.K., n.d.), 60 percent of the world's wireless Internet users use i-mode, 39 percent use WAP, and 1 percent use Palm middleware in 2002. Table 1 compares i-mode and WAP, along with details of each.

WAP (Wireless Application Protocol). WAP (2003) is an open, global specification that allows users with mobile stations to easily access and interact with information and services instantly. It is a very flexible standard including most wireless networks, which comprise CDPD, CDMA, GSM, PDC, PHS, TDMA, FLEX, ReFLEX, iDEN, TETRA, DECT, DataTAC, Mobitex, and GRPS. It is supported by most operating systems and was specifically engineered for mobile stations, including PalmOS, EPOC, Windows CE, FLEXOS, OS/9, and JavaOS. The most important technology applied by WAP is probably the WAP Gateway, which translates requests from the WAP protocol stack to the WWW stack so they can be submitted to Web servers. For example, requests from mobile stations are sent as a URL through the network to the WAP Gateway; responses are sent from the Web server to the WAP Gateway in HTML and are then translated to WML and sent to the mobile stations. Although WAP supports HTML and XML, its host language is WML (Wireless Markup Language), which is a markup language based on XML that is intended for use in specifying content and user interfaces for mobile stations. WAP also supports WMLScript, which is similar to JavaScript but makes minimal demands on memory and CPU power because it does not contain many of the unnecessary functions found in other scripting languages.

Table 1. Comparisons of two major kinds of mobile middleware
DeveloperWAP ForumNTT DoCoMo
FunctionA protocolA complete mobile Internet service
Host LanguageWML (Wireless Markup Language)CHTML (Compact HTML)
Major TechnologyWAP GatewayTCP/IP modifications
Key FeaturesWidely adopted and flexibleHighest number of users and easy to use

i-mode. i-mode (NTT DoCoMO, Inc. n.d.) is the full-color, always-on, and packet-switched Internet service for cellular phones offered by NTT DoCoMo. Introduced in February 1999, it has attracted over 36 million subscribers worldwide. With i-mode, cellular phone users can easily access more than 62,000 Internet sites, as well as specialized services such as e-mail, on-line shopping and banking, ticket reservations, and personalized ringtones that can be downloaded for their phones. The i-mode network structure not only provides access to i-mode and i-mode-compatible contents through the Internet, but also uses a dedicated leased-line circuit for added security. i-mode is the only network in the world that currently allows subscribers continuous access to the Internet via cellular phones. Users are charged based on the volume of data transmitted, rather than the amount of time spent connected. In spring 2001, NTT 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 videos and other bandwidth-intensive content with its high-speed packet data communications.


Both WAP and i-mode are built on top of existing network protocols such as Internet Protocol (IP) and Transmission Control Protocol (TCP). IP provides a network routing service for upper layer protocols like TCP, which transports data reliably between two end parties of a network connection. This reliable data delivery service is crucial to the success of transactions in mobile commerce systems. In a wireless environment, IP and TCP require significant modification in order to adapt to features like mobility and radio communication.

Mobile IP. Mobile IP (The IETF Working Group, 2003) 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 the error-prone nature of data transmission on wireless channels, which often suffer from frequent handoffs and disconnections. In order to optimize reliable data transport performance, a number of variants of TCP have been suggested for mobile networks. An idea proposed by Yavatkar and Bhagawat (1994) was to split the path between the mobile node and the fixed node into two separate sub-paths: one of which covers the wireless links and the other the wired links. This approach limits the TCP performance degradation to that incurred in the "short" wireless link connection. The "packet caching" scheme proposed by Balakrishnan et al. (1995) tries to reduce the TCP retransmission overhead due to handoff, while the "fast retransmission" scheme suggested by Caceres and Iftode (1996) utilizes the fast retransmission option immediately after handoff is completed to achieve smooth TCP performance during handoff.

Wireless Local Area Networks

Devices used in wireless local area network (WLAN) technologies are light-weight, portable, and flexible in network configuration. As a result, 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 and data packets are relayed by the 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.

Table 2. Major WLAN standards
StandardMaximum Data RateTypical Range (m)ModulationFrequency Band
Bluetooth1 Mbps5 – 10GFSK2.4 GHz
802.11b (Wi-Fi)11 Mbps50 – 100HR-DSSS2.4 GHz
802.11a54 Mbps50 – 100OFDM5 GHz
HyperLAN254 Mbps50 – 300OFDM5 GHz
802.11g54 Mbps50 – 150OFDM2.4 GHz

In Table 2, major WLAN technologies are compared in terms of their 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, resulting in different throughputs and coverage ranges. 

In general, Bluetooth technology supports very limited coverage range and throughput and is thus only suitable for applications in personal area networks. In many parts of the world, the IEEE 802.11b (Wi-Fi) system has become the most popular wireless network and is widely used in offices, homes, and public spaces such as airports, shopping malls, and restaurants. However, many experts predict that with their much higher transmission speeds, 802.11a and 802.11g will replace 802.11b in the near future.

Wireless Metropolitan Area Network

The most important technology in this category is the cellular wireless network, with which cellular system users can conduct mobile commerce operations using their cellular phones. Under this scenario, a cellular phone connects directly to the closest base station, where communications are relayed to the service site through a radio access network (RAN) and other fixed 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 and other data applications. Table 3 lists the classifications of standards in first generation (1G), second generation (2G, 2.5G), and third generation (3G) wireless cellular networks. 1G systems such as the advanced mobile phone system (AMPS) and total access control system (TACS) are becoming obsolete, and thus will not play a significant role in mobile commerce systems. The global system for mobile communications (GSM) and its enhancement general packet radio service (GPRS) have primarily been developed and deployed in Europe. GPRS can support data rates of only about 100 kbps, but its upgraded version—enhanced data for global evolution (EDGE)—is capable of supporting 384 kbps. In the United States, wireless operators use time division multiple access (TDMA) and code division multiple access (CDMA) technologies in their cellular networks.

Table 3. Major cellular wireless networks
GenerationRadio ChannelsSwitching TechniqueStandards (Examples)
1GAnalog voice channels Digital control channelsCircuit-switchedAMPS TACS
2GDigital channelsCircuit-switchedGSM TDMA
2.5GDigital channelsPacket-switchedGPRS EDGE
3GDigital channelsPacket-switchedCDMA2000 WCDMA
4GDigital channelsPacket-switchedWiMAX

Currently, most cellular wireless networks follow 2G or 2.5G standards. However, there is no doubt that in the near future, 3G systems with quality-of-service (QoS) capability will dominate wireless cellular services. The two main standards for 3G are Wideband CDMA (WCDMA), proposed by Ericsson, and CDMA2000, proposed by Qualcomm. Both use direct sequence spread spectrum (DSSS) in a 5-MHz bandwidth. Technical differences between them include their different chip rate, frame time, spectrum used, and time synchronization mechanism. The WCDMA system can inter-network with GSM networks and has been strongly supported by the European Union, which calls it the Universal Mobile Telecommunications System (UMTS). CDMA2000 is backward-compatible with IS-95, which is widely deployed in the United States.

In a wireless cellular system, a wired network known as a radio access network (RAN) is employed to connect radio transceivers with core networks. Two examples of existing RAN architectures are UTRAN (UTRAN overall description, 1999) and IOS (MSC to BS interface inter-operability specification, 1999). Since UTRAN is the new radio access network designed especially for 3G UMTS, the universal mobile telecommunications system, it deserves further description.

Figure 1. UMTS and UTRAN architecture (Vriendt et al., 2002)

The architecture and components of UMTS and UMTS Terrestrial Radio Access Network (UTRAN) are shown in Figure 1 (Vriendt et al., 2002). At the highest level, the UMTS network structure consists of the core network and UTRAN. The network subsystem (NSS) of GSM/GPRS is reused as much as possible in the UMTS core network. Two service domains are supported in the core network, circuit switching (CS) and packet switching (PS). By moving the NSS transcoder function from the base station subsystem to the core network, CS provides voice and circuit-switched data services. Evolving from GPRS, the packet-switched service provided by PS optimizes functional relationships between the core network and UTRAN. UTRAN consists of radio network subsystems (RNS), each of which contains one radio network controller (RNC) and at least one Node B (base station). The RNC controls the logical resources for Node Bs in the UTRAN, while the Node Bs in turn manage radio transmission and reception for one or more cells and provide logical resources to the RNC.

Wireless Wide Area Networks

In large geographic areas that lack the infrastructure of wireless cellular networks, satellite systems can be utilized to provide wireless communication services. Communication through satellites is very similar to the scenario in cellular systems, apart from the differences in transmission distance and coverage range. For example, a user in an airplane can use a satellite communication system to conduct mobile commerce transactions. The messages will first be sent to a base station then forwarded to service provider sites. Satellite systems are generally categorized by the height of the orbit. Table 4 summaries their characteristics.

Table 4. Major satellite systems
Satellite SystemHeight of Orbit (km)CoverageLatency (ms)
Geosynchronous Earth Orbit (GEO)35,8631/3 of earth surface270
Medium Earth Orbit (MEO)5,000 – 12,000A few thousand kilometers35 – 85
Low Earth Orbit (LEO)500 – 1,500Two thousand kilometers1 – 7

In general, there are three communication configurations in satellite systems: point-to-point links, broadcast links, and VSAT. Point-to-point link configuration means two ground-based antennas establish a point-to-point link through a satellite. Broadcast links are configured so that a single ground-based transmitter can establish a multicast channel with a number of ground-based receivers through the satellite. When subscriber stations are equipped with a low-cost very small aperture terminal (VSAT) system, they share satellite transmission capacity for transmission to a hub station and the hub station can exchange and relay messages between subscribers. VSAT can thus provide two-way communication among subscribers.

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