1.0 INTRODUCTION

Mobile Technology is becoming widely accepted throughout the world. Both the number of subscribers and the cellular coverage areas are increasing continuously. In addition, more advanced digital cellular coverage is on the rise, allowing data and voice to be mixed seamlessly.

The most extravagant claims for Mobile technology surround mobile services, especially mobile data. If the cell phone vendors are to be believed, we will soon be able to watch high-definition TV streamed live to a pocket-sized panel, while surfing the web and participating in a videoconference.

Mobile services are constantly enhanced with new capabilities associated with the transition stages of the mobile networks. Mobile service is the delivery of data and voice services for a uniform solution, enable ease of operation and administration, and accommodate existing subscriber capacity, message throughput, future growth, and reliability.

In this paper, we will discuss mobile data and voice services.

2.0 MOBILE SEVICES

There are two basic types of services: data (also referred to as bearer services) and telephony (also referred to as teleservices or voice services). Data services provide the capacity necessary to transmit appropriate data signals between two access points creating an interface to the network. Telephony services are mainly voice services that provide subscribers with the complete capability (including necessary terminal equipment) to communicate with other subscribers.

2.1.0 Mobile Data Services

This is the provision of the required capacity to send data signals between two access points. This is classified into two: Mobility, and Content and Connectivity.

2.1.1 Mobility

This is categorised into messaging services and location-based services.

(I) Messaging Services

Messaging allows subscribers to receive and send short text messages -essentially the same as paging, but with the data appearing on a mobile phone instead of a separate pager.

• Short Message

The only messaging standard to have achieved widespread acceptance is the short message service (SMS). It began as part of the original Global system for Mobile Communication (GSM) specification but has since spread to all the other digital system, some of which have improved on it.

SMS's greatest limitation is hinted in its name: Messages have to be short. GSM imposes a limit of only 160 bytes or characters ---the length of this paragraph.

The length limit is caused by the way that SMS is transmitted. It usually rides on the control channels, the same frequencies or time slots used for call setup information. This means that users can send or receive SMS message while they are making a phone call, so they need a hands-free kit to read the screen or type on the keypad. Different systems use different types of control channels, so the precise limit depends on the system.

• Cell broadcast

If the same information needs to be sent to many different users, broadcasting is more efficient than routing a separate transmission to each one. This is the theory behind the Cell Broadcast Service (CBS), a variant of SMS used only in GSM, each message is known as a page and can be only 93 bytes long, but up to 15 pages can be concatenated for a total message length of 1395 bytes - enough for several paragraphs of text or a short program. Typical applications include traffic congestion warnings and reports on accidents.

• Dual-Tone Multifrequency (DTMF)

DTMF is a tone signalling scheme often used for various control purposes via the telephone network, such as remote control of an answering machine. GSM supports full-originating DTMF.

• Facsimile Group III

GSM supports CCITT Group 3 facsimile. As standard fax machines are designed to be connected to a telephone using analog signals, a special fax converter connected to the exchange is used in the GSM system. This enables a GSM-connected fax to communicate with any analog fax in the network.

• Fax Mail

With this service, the subscriber can receive fax messages at any fax machine. The messages are stored in a service center from which they can be retrieved by the subscriber via a personal security code to the desired fax number.

• Voice Mail

This service is actually an answering machine within the network, which is controlled by the subscriber. Calls can be forwarded to the subscriber's voice-mail box and the subscriber checks for messages via a personal security code.

Supplementary Services

GSM supports a comprehensive set of supplementary services that can complement and support both telephony and data services. Supplementary services are defined by GSM and are characterized as revenue-generating features. A partial listing of supplementary services follows.

• Call Forwarding-This service gives the subscriber the ability to forward incoming calls to another number if the called mobile unit is not reachable, if it is busy, if there is no reply, or if call forwarding is allowed unconditionally.
• Barring of Outgoing Calls-This service makes it possible for a mobile subscriber to prevent all outgoing calls.
• Barring of Incoming Calls-This function allows the subscriber to prevent incoming calls. The following two conditions for incoming call barring exists: baring of all incoming calls and barring of incoming calls when roaming outside the home public land mobile network(PLMN).
• Advice of Charge (AoC)-The AoC service provides the mobile subscriber with an estimate of the call charges. There are two types of AoC information: one that provides the subscriber with an estimate of the bill and one that can be used for immediate charging purposes. AoC for data calls is provided on the basis of time measurements.
• Call Hold-This service enables the subscriber to interrupt an ongoing call and then subsequently re-establish the call. The call hold service is only applicable to normal voice service.
• Call Waiting-This service enables the mobile subscriber to be notified of an incoming call during a conversation. The subscriber can answer, reject, or ignore the incoming call. Call waiting is applicable to all GSM telecommunications services using a circuit-switched connection.
• Multiparty Service-The multiparty service enables a mobile subscriber to establish a multiparty conversation-that is, a simultaneous conversation between three and six subscribers. This service is only applicable to normal voices.
• Calling Line Identification Presentation/Restriction-These services supply the called party with the integrated services digital network (ISDN) number of the calling party. The restriction service enables the calling party to restrict the presentation. The restriction overrides the presentation.
• Closed User Groups (CUGs)-CUGs are generally comparable to a PBX. They are a group of subscribers who are capable of only calling themselves and certain numbers.

(II) Location -Based Services

There are two solutions for the cellular location-based service; network-based location and the handset-based location.

• Network-Based location

Network-based caller location systems employ either the time-difference of arrival (TDOA) approach or the angle of arrival (AOA) approach to determine the caller's location. The TDOA measures the differences in the times of a signal at the cell sites or the base stations. The caller's location can be determined if the signal is received at a minimum of three base stations.

The AOA uses phased-array antennas to compute the angles at which the signal arrives at the base station. A minimum of two sites is required to compute the caller's location.

Some network operators combine the TDOA and AOA to provide the location based service.

• Handset-based location

This integrates Global Positioning System (GPS) with cellular communication through the installation of a GPS chipset in the mobile handset phone. With selective availability turned off permanently, this technology would accurately locate a caller :-

What Is GPS?

GPS is a satellite navigation system designed to provide instantaneous position, velocity and time information almost anywhere on the globe at any time, and in any weather, usually within a few meters.

GPS is the most significant recent advancement in navigation and positioning technology. In the past, the stars were used for navigation. Today's world requires greater accuracy. The new constellation of artificial stars provided by the Global Positioning System serves this important need.

GPS operates 24 hours a day, in all weather conditions, and can be used worldwide for precise navigation on land, on water and even in the air.

GPS uses a constellation of 24 satellites in precise orbits approximately 11,000 miles above the earth. This constellation is known as the Initial Operational Capability. The satellites transmit data via high frequency radio waves back to earth; a GPS receiver such as mobile handset can process this data to triangulate its precise location on the globe.

GPS consist of three segments; the space segment, the control segment and the user segment.

Space Segment

The Space Segment of the system consists of the GPS satellites. These space vehicles (SVs) send radio signals from space.
The nominal GPS Operational Constellation consists of 24 satellites that orbit the earth in 12 hours. There are often more than 24 operational satellites as new ones are launched to replace older satellites. The satellite orbits repeat almost the same ground track (as the earth turns beneath them) once each day. The orbit altitude is such that the satellites repeat the same track and configuration over any point approximately each 24 hours (4 minutes earlier each day). There are six orbital planes (with nominally four SVs in each), equally spaced (60 degrees apart), and inclined at about fifty-five degrees with respect to the equatorial plane. This constellation provides the user with between five and eight SVs visible from any point on the earth.

Control Segment

The Control Segment consists of a system of tracking stations located around the world.
These monitor stations measure signals from the SVs which are incorporated into orbital models for each satellite. The models compute precise orbital data (ephemeris) and SV clock corrections for each satellite. The Master Control station uploads ephemeris and clock data to the SVs. The SVs then send subsets of the orbital ephemeris data to GPS receivers over radio signals.

User Segment

The GPS User Segment consists of the GPS receivers and the user community. GPS receivers convert SV signals into position, velocity, and time estimates. Four satellites are required to compute the four dimensions of X, Y, Z (position) and Time. GPS receivers are used for navigation, positioning, time dissemination, and other research.

• Navigation in three dimensions is the primary function of GPS. Navigation receivers are made for aircraft, ships, ground vehicles, and for hand carrying by individuals.
• Precise positioning is possible using GPS receivers at reference locations providing corrections and relative positioning data for remote receivers.
• Time and frequency dissemination, based on the precise clocks on board the SVs and controlled by the monitor stations, is another use for GPS. Astronomical observatories, telecommunications facilities, and laboratory standards can be set to precise time signals or controlled to accurate frequencies by special purpose GPS receivers.
• Research projects have used GPS signals to measure atmospheric parameters.

How GPS Determines Your Position

GPS uses satellite ranging to triangulate your position. In other words, the GPS unit simply measures the travel time of the signals transmitted from the satellites, then multiplies them by the speed of light to determine exactly how far the unit is from every satellite.

GPS is complicated by two factors. First, the satellites are moving, so they continuously transmit their own position, rather than sending a simple radio pulse. Second, there is return path from the receiver back to the satellite. The satellites overcome this by transmitting the precise time, measured by an onboard atomic clock. A receiver can calculate its distance from each satellite by comparing the received time with its own clock, then triangulating. The receiver needs to lock on four satellites simultaneously: three to triangulate and one extra to keep its clock synchronized with the network.

Fig 1: Measurement o code-phase arrival times at least four satellites are used to estimate four quantise: position in three dimensions (X, Y, Z) and GPS time (T)

GPS Accuracy

There are two transmission codes; the P code (Precision code) for military use, and the C/A code (Civilian Access code) for civilian use.

The highest accuracy levels were to be reserved for the military. However, once in operation, the civilian GPS receivers using the C/A code proved to be more accurate. Consequently, the military developed a system for randomly degrading the accuracy of the signals being transmitted to civilian GPS receivers. This intentional degradation in accuracy is called Selective Availability or S/A. This reduced the civilian GPS accuracy levels to being within 100 meters or less, 95% of the time. However, typical accuracy for most users averaged between 20 and 50 meters the majority of the time.

Effective May 2, 2000 selective availability (S/A) has been eliminated. There is now technology to localize the control system to deny GPS signals to selected areas. It is not often that your electronics products increase in value after you've purchased them. Now boaters, aviators, drivers, hikers, hunters, and outdoor enthusiasts of all types can locate their position up to ten times more precisely (within 10 to 20 meters) and navigate their way through unfamiliar terrain. Anglers can now return to their favourite spot on a lake or river instead of just their favourite area.
The decision to allow civilians so much accuracy in location information was finally made because GPS is continually playing a more important role in the lives of people around the world - it's becoming a national utility. GPS is the global standard in navigation.

2.1.2 Content and Connectivity

(I) Evolution of Mobile Communications

Electromagnetic waves were first discovered as a communications medium at the end of the 19th century. The first systems offering mobile telephone service (car phone) were introduced in the late 1940s in the United States and in the early 1950s in Europe. Those early single cell systems were severely constrained by restricted mobility, low capacity, limited service, and poor speech quality. The equipment was heavy, bulky, expensive, and susceptible to interference.

First Generation (1G): Analog Cellular

The introduction of cellular systems in the late 1970s and early 1980s represented a quantum leap in mobile communication (especially in capacity and mobility). Semiconductor technology and microprocessors made smaller, lighter weight, and more sophisticated mobile systems a practical reality for many more users. These 1G cellular systems still transmit only analog voice information. The most prominent 1G systems are Advanced Mobile Phone System (AMPS), Nordic Mobile Telephone (NMT), and Total Access Communication System (TACS).

Second Generation (2G): Multiple Digital Systems

The development of 2G cellular systems was driven by the need to improve transmission quality, system capacity, and coverage. Further advances in semiconductor technology and microwave devices brought digital transmission to mobile communications. Speech transmission still dominates the airways, but the demands for fax, short message, and data transmissions are growing rapidly. Supplementary services such as fraud prevention and encrypting of user data have become standard features that are comparable to those in fixed networks. 2G cellular systems include GSM, Digital AMPS (D-AMPS), code division multiple access (CDMA), and Personal Digital Communication (PDC). Many standards are used only in one country or region, and most are incompatible. GSM is the most successful family of cellular standards (GSM900, GSM-railway [GSM-R], GSM1800, GSM1900, and GSM400).

2G to 3G: GSM Evolution

Phase 1 of the standardization of GSM900 was completed by the European Telecommunications Standards Institute (ETSI) in 1990 and included all necessary definitions for the GSM network operations. Several teleservices and bearer services have been defined (including data transmission up to 9.6 kbps), but only some very basic supplementary services were offered. As a result, GSM standards were enhanced in Phase 2 (1995) to incorporate a large variety of supplementary services that were comparable to digital fixed network Integrated Services Digital Network (ISDN) standards. In 1996, ETSI decided to further enhance GSM in annual Phase 2+ releases that incorporate 3G capabilities.

GSM Phase 2+ releases have introduced important 3G features such as Intelligent Network (IN) services with Customized Application for Mobile Enhanced Logic (CAMEL), Enhanced Speech Compression/Decompression (CODEC), Enhanced Full Rate (EFR), and Adaptive Multirate (AMR), high-data rate services and new transmission principles with High-Speed Circuit-Switched Data (HSCSD), general packet radio service (GPRS), and Enhanced Data Rates For GSM Evolution (EDGE). UMTS is a 3G GSM successor standard that is downward-compatible with GSM, using the GSM Phase 2+ enhanced core network.

IMT-2000

IMT-2000 is a set of requirements defined by the International Telecommunications Union (ITU). IMT stands for International Mobile Telecommunications, and "2000" represents both the scheduled year for initial trial systems and the frequency range of 2000 MHz (WARC'92: 1885-2025 MHz and 2110-2200 MHz). All 3G standards have been developed by regional standards developing organizations (SDOs). 17 IMT-2000 standards proposals (11 for terrestrial systems and 6 for mobile satellite systems (MSSs).) have been accepted by ITU as IMT-2000 standards. The specification for the Radio Transmission Technology (RTT) was released at the end of 1999.
The most important IMT-2000 proposals are the UMTS (W-CDMA) as the successor to GSM, CDMA2000 as the interim standard '95 (IS-95) successor, and time division-synchronous CDMA (TD-SCDMA) (universal wireless communication-136 [UWC-136]/EDGE) as TDMA-based enhancements to D-AMPS/GSM-all of which are leading previous standards toward the ultimate goal of IMT-2000.

The main characteristics of 3G systems, known collectively as IMT-2000, are a single family of compatible standards that have the following characteristics:

• Used worldwide
• Used for all mobile applications
• Support both packet-switched (PS) and circuit-switched (CS) data transmission
• Offer high data rates up to 2 Mbps (depending on mobility/velocity)
• Offer high spectrum efficiency

Fig.2: Multiple Standards for Different Applications and Countries

Fig.3: Evolutionary Concept

(II) The GSM Network

GSM provides recommendations, not requirements. The GSM specifications define the functions and interface requirements in detail but do not address the hardware. The reason for this is to limit the designers as few as possible but still to make it possible for the operators to buy equipment from different suppliers, to ensure flexible integrated service. The GSM network is divided into three major systems: the switching system (SS), the base station system (BSS), and the operation and support system (OSS). The basic GSM network elements are shown in Fig 4.

Fig:4. GSM Network Elements

The Switching System

The switching system (SS) is responsible for performing call processing and subscriber-related functions. The switching system includes the following functional units.

• Home Location Register (HLR)-The HLR is a database used for storage and management of subscriptions. The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status. When an individual buys a subscription from one of the PCS operators, he or she is registered in the HLR of that operator.
• Mobile Services Switching Center (MSC)-The MSC performs the telephony switching functions of the system. It controls calls to and from other telephone and data systems. It also performs such functions as toll ticketing, network interfacing, common channel signalling, and others.
• Visitor Location Register (VLR)-The VLR is a database that contains temporary information about subscribers that is needed by the MSC in order to service visiting subscribers. The VLR is always integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that MSC will request data about the mobile station from the HLR. Later, if the mobile station makes a call, the VLR will have the information needed for call setup without having to interrogate the HLR each time.
• Authentication Center (AUC)-A unit called the AUC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The AUC protects network operators from different types of fraud found in today's cellular world.
• Equipment Identity Register (EIR)-The EIR is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. The AUC and EIR are implemented as stand-alone nodes or as a combined AUC/EIR node.

The Base Station System (BSS)

All radio-related functions are performed in the BSS, which consists of base station controllers (BSCs) and the base transceiver stations (BTSs).

• BSC-The BSC provides all the control functions and physical links between the MSC and BTS. It is a high-capacity switch that provides functions such as handover, cell configuration data, and control of radio frequency (RF) power levels in base transceiver stations. A number of BSCs are served by an MSC.
• BTS-The BTS handles the radio interface to the mobile station. The BTS is the radio equipment (transceivers and antennas) needed to service each cell in the network. A group of BTSs are controlled by a BSC.

The Operation and Support System

The operations and maintenance center (OMC) is connected to all equipment in the switching system and to the BSC. The implementation of OMC is called the operation and support system (OSS). The OSS is the functional entity from which the network operator monitors and controls the system. The purpose of OSS is to offer the customer cost-effective support for centralized, regional, and local operational and maintenance activities that are required for a GSM network. An important function of OSS is to provide a network overview and support the maintenance activities of different operation and maintenance organizations.

Additional Functional Elements

Other functional elements shown in Fig 4 are as follows:

• Message Center (MXE)-The MXE is a node that provides integrated voice, fax, and data messaging. Specifically, the MXE handles short message service, cell broadcast, voice mail, fax mail, e-mail, and notification.
• Mobile Service Node (MSN)-The MSN is the node that handles the mobile intelligent network (IN) services.
• Gateway Mobile Services Switching Center (GMSC)-A gateway is a node used to interconnect two networks. The gateway is often implemented in an MSC. The MSC is then referred to as the GMSC.
• GSM Interworking Unit (GIWU)-The GIWU consists of both hardware and software that provides an interface to various networks for data communications. Through the GIWU, users can alternate between speech and data during the same call. The GIWU hardware equipment is physically located at the MSC/VLR.

GSM Network Areas

The GSM network is made up of geographic areas. As shown in Fig 5, these areas include cells, location areas (LAs), MSC/VLR service areas, and public land mobile network (PLMN) areas.

Fig. 5: Network Areas

The cell is the area given radio coverage by one base transceiver station. The GSM network identifies each cell via the cell global identity (CGI) number assigned to each cell. The location area is a group of cells. It is the area in which the subscriber is paged. Each LA is served by one or more base station controllers, yet only by a single MSC Fig 6). Each LA is assigned a location area identity (LAI) number.

Fig. 6: Location Areas

An MSC/VLR service area represents the part of the GSM network that is covered by one MSC and which is reachable, as it is registered in the VLR of the MSC (see Fig. 7).

Fig. 7: MSC/VLR Service Areas

The PLMN service area is an area served by one network operator.

(III) The UMTS Network

Universal Mobile Telecommunications System (UMTS) is envisioned as the successor to Global System for Mobile Communications (GSM). UMTS also addresses the growing demand of mobile and Internet applications for new capacity in the overcrowded mobile communications sky. The network increases transmission speed to 2 Mbps per mobile user and establishes a global roaming standard.

UMTS, also referred to as wideband code division multiple access (W-CDMA), is one of the most significant advances in the evolution of telecommunications into 3G networks. UMTS allows many more applications to be introduced to a worldwide base of users and provides a vital link between today's multiple GSM systems and the ultimate single worldwide standard for all mobile telecommunications, International Mobile Telecommunications-2000 (IMT-2000).

UMTS (Rel. '99) incorporates enhanced GSM Phase 2+ Core Networks (CN) with GPRS and CAMEL. This enables network operators to enjoy the improved cost-efficiency of UMTS while protecting their 2G investments and reducing the risks of implementation.

In UMTS release 1 (Rel. '99), a new radio access network UMTS terrestrial radio access network (UTRAN) is introduced. UTRAN, the UMTS radio access network (RAN), is connected via the Iu to the GSM Phase 2+ core network (CN). The Iu is the UTRAN interface between the radio network controller (RNC) and CN; the UTRAN interface between RNC and the packet-switched domain of the CN (Iu-PS) is used for PS data and the UTRAN interface between RNC and the circuit-switched domain of the CN (Iu-CS) is used for CS data.

"GSM-only" mobile stations (MSs) will be connected to the network via the GSM air (radio) interface (Um). UMTS/GSM dual-mode user equipment (UE) will be connected to the network via UMTS air (radio) interface (Uu) at very high data rates (up to almost 2 Mbps). Outside the UMTS service area, UMTS/GSM UE will be connected to the network at reduced data rates via the Um.

Maximum data rates are 115 kbps for CS data by HSCSD, 171 kbps for PS data by GPRS, and 553 kbps by EDGE. Handover between UMTS and GSM is supported, and handover between UMTS and other 3G systems (e.g., multicarrier CDMA [MC-CDMA]) will be supported to achieve true worldwide access.

GPRS - The most important evolutionary step of GSM toward UMTS is GPRS. GPRS introduces packet-switched (PS) into the GSM CN and allows direct access to packet data networks (PDNs). This enables high-data rate PS transmission well beyond the 64 kbps limit of ISDN through the GSM CN, a necessity for UMTS data transmission rates of up to 2 Mbps. GPRS prepares and optimizes the CN for high-data rate PS transmission, as does UMTS with UTRAN over the RAN. Thus, GPRS is a prerequisite for the UMTS introduction.

Two functional units extend the GSM NSS architecture for GPRS PS services: the GGSN and the SGSN. The GGSN has functions comparable to a gateway MSC (GMSC). The SGSN resides at the same hierarchical level as a visited MSC (VMSC)/VLR and therefore performs comparable functions such as routing and mobility management.

CAMEL - CAMEL enables worldwide access to operator-specific IN applications such as prepaid, call screening, and supervision. CAMEL is the primary GSM Phase 2+ enhancement for the introduction of the UMTS virtual home environment (VHE) concept. VHE is a platform for flexible service definition (collection of service creation tools) that enables the operator to modify or enhance existing services and/or define new services. Furthermore, VHE enables worldwide access to these operator-specific services in every GSM and UMTS PLMN and introduces location-based services (by interaction with GSM/UMTS mobility management). A CSE and a new common control signaling system 7 (SS7) (CCS7) protocol, the CAMEL application part (CAP), are required on the CN to introduce CAMEL.

(IV) Wireless Application Protocol (WAP)

This is an application environment and set of communication protocols for wireless devices designed to enable manufacturer-, vendor-, and technology-independent access to the Internet and advanced telephony services.
WAP bridges the gap between the mobile world and the Internet as well as corporate intranets and offers the ability to deliver an unlimited range of mobile value-added services to subscribers-independent of their network, bearer, and terminal. Mobile subscribers can access the same wealth of information from a pocket-sized device as they can from the desktop.

WAP is a global standard and is not controlled by any single company. Ericsson, Nokia, Motorola, and Unwired Planet founded the WAP Forum in the summer of 1997 with the initial purpose of defining an industry-wide specification for developing applications over wireless communications networks. The WAP specifications define a set of protocols in application, session, transaction, security, and transport layers, which enable operators, manufacturers, and applications providers to meet the challenges in advanced wireless service differentiation and fast/flexible service creation.

Operators

For wireless network operators, WAP promises to decrease churn, cut costs, and increase the subscriber base both by improving existing services, such as interfaces to voice-mail and prepaid systems, and facilitating an unlimited range of new value-added services and applications, such as account management and billing inquiries. New applications can be introduced quickly and easily without the need for additional infrastructure or modifications to the phone. This allows operators to differentiate themselves from their competitors with new, customized information services. WAP is an interoperable framework, enabling the provision of end-to-end turnkey solutions that creates a lasting competitive advantage, build consumer loyalty, and increase revenues.

Content Providers

Applications are written in wireless markup language (WML), which is a subset of extensible markup language (XML). Using the same model as the Internet, WAP enables content and application developers to grasp the tag-based WML that paves the way for services to be written and deployed within an operator's network quickly and easily. As WAP is a global and interoperable open standard, content providers have immediate access to a wealth of potential customers who will seek such applications to enhance the service offerings given to their own existing and potential subscriber base. Mobile consumers are becoming hungrier to receive increased functionality and value-added services from their mobile devices, and WAP opens the door to this untapped market. This presents developers with significant revenue opportunities.

End Users

End users of WAP, benefit from easy, secure access to relevant Internet information and services such as unified messaging, banking, and entertainment through their mobile devices. Intranet information such as corporate databases can be accessed via WAP technology. A wide range of handset can support WAP; users have significant freedom of choice when selecting mobile terminals and the applications they support. Users can receive and request information in a controlled, fast, and low-cost environment, a fact that renders WAP services more attractive to consumers who demand more value and functionality from their mobile terminals.

WAP's push capability enables weather and travel information providers to use WAP. This push mechanism affords a distinct advantage over the WWW and represents tremendous potential for both information providers and mobile operators.

WAP utilizes Internet standards such as XML, user datagram protocol (UDP), and Internet protocol (IP). Many of the protocols are based on Internet standards such as hypertext transfer protocol (HTTP) and TLS but have been optimized for the unique constraints of the wireless environment: low bandwidth, high latency, and less connection stability.

Internet standards such as hypertext markup language (HTML), HTTP, TLS and transmission control protocol (TCP) are inefficient over mobile networks, requiring large amounts of mainly text-based data to be sent. Standard HTML content cannot be effectively displayed on the small-size screens of pocket-sized mobile phones and pagers.

WAP utilizes binary transmission for greater compression of data and is optimized for long latency and low bandwidth. WAP sessions cope with intermittent coverage and can operate over a wide variety of wireless transports.

WML and wireless markup language script (WMLScript) are used to produce WAP content. They make optimum use of small displays, and navigation may be performed with one hand. WAP content is scalable from a two-line text display on a basic device to a full graphic screen on the latest smart phones and communicators.

The lightweight WAP protocol stack is designed to minimize the required bandwidth and maximize the number of wireless network types that can deliver WAP content. Multiple networks are targeted. These include global system for mobile communications (GSM) 900, 1,800, and 1,900 MHz; interim standard (IS)-136; Digital European Cordless Communication (DECT); Time-Division Multiple Access (TDMA), Personal Communications Service (PCS), FLEX, and Code Division Multiple Access (CDMA). All network technologies and bearers are supported, including Short Message Service (SMS), USSD, Circuit-Switched Cellular Data (CSD), cellular digital packet data (CDPD), and general packet radio service (GPRS).

As WAP is based on a scalable layered architecture, each layer can develop independently of the others. This makes it possible to introduce new bearers or to use new transport protocols without major changes in the other layers.

Architecture of the WAP Gateway

Fig.8: Architecture of the WAP Gateway

WDP

The WAP datagram protocol (WDP) is the transport layer that sends and receives messages via any available bearer network, including SMS, USSD, CSD, CDPD, IS-136 packet data, and GPRS.

WTLS

Wireless transport layer security (WTLS), an optional security layer, has encryption facilities that provide the secure transport service required by many applications, such as e-commerce.

WTP

The WAP transaction protocol (WTP) layer provides transaction support, adding reliability to the datagram service provided by WDP.

WSP

The WAP session protocol (WSP) layer provides a lightweight session layer to allow efficient exchange of data between applications.

HTTP Interface

The HTTP interface serves to retrieve WAP content from the Internet requested by the mobile device.

(V) i-Mode

i-mode is a WAP-like mobile internet service originating in Japan introduced by NTTDoCoMo (Nippon Telephone and Telegraph DoCoMo - doco mo means "anyplace you go" in Japanese and the acronym stands for "Do Communication Over the Mobile Network."). This was invented by Mari Matsunga and was lunched in February, 1999.

The markup language used for i-mode is Compact HTML or cHTML. cHTML is a subset of HTML that leaves out coding for JPEG images, tables, image map, multiple character fonts and styles, background color or images, frames, and cascading style sheets. These things are excluded due to the low bandwidth and limited screen-size of cellphones. The internet connection of i-mode is always on.

i-mode allow users to do their e-mail and text messaging. Users can also view news and horoscopes, and download ring tones, cartoon characters and train times. Users can connect to any site that supports cHTML approved by NTTDoCoMo.

What are the differences between i-mode and WAP?

The biggest difference of WAP and i-Mode is certainly the always-on technology which makes i-Mode so popular. In contrary to WAP, i-Mode phone is always connected to the internet and the user only pays for the amount of data downloaded. So far, with the GSM networks, this is not the case for WAP. GPRS is also always on.

Currently, i-Mode is the user-friendlier technology. Another feature which WAP doesn't have is the 256 colour capability of some i-Mode devices, which makes the whole appearance look much better and attractive. i-Mode screens also use many graphics to make the navigation for the user easier.

The transmission rates of i-Mode are just about the same as for WAP but since the service is always-on, it saves all the dial-up time.

WAP and i-Mode are both capable of sending and receiving e-mail. In this category, WAP is ahead, because i-Mode e-mail is restricted to 500 bytes.

At this time, if one compares the 2 technologies, i-Mode is the clear winner of the contest.

2.2.0 Mobile Voice Services

2.2.1 Basic Voice

Voice infrastructure

Mobile networks are relatively new; all switching is digital, and all mobile phones use tone dialing, which represents digits by musical notes.

Station controllers

The first step in a digital cell phone network is the link from the BTS to the Base Station Controller (BSC). This simply converts signals from a base station to a more landline- friendly format. Analog networks need to place the BSC at the BTS itself so that analog radio waves can be converted to digital signals as soon as they are received. Digital networks prefer to locate it a little away, which keeps costs down because it allows several base stations to share the BSC.

Switching Centers

The most complex component in a mobile voice network is the Mobile Switching center( MSC). Analogous to a telephone exchange, the MSC is responsible for keeping track of users and sending them calls when necessary. A network usually contains many MSCs, each of which is responsible for several clusters of cells.
Each MSC is linked to several databases, which are used to keep track of users' locations. These can be stored on a computer at the MSC network.

Trunking

In the early cellular networks, all MSCs were meshed-each was connected to each other. This quickly grew uncontrollably, Trunking Switching Centers ( TSCs) became common. These simply aggregate connections from several MSCs and combine them in very high-capacity cable.

Gateways

The Gateway Mobile Swithching center (GMSC) sits at the top of the switching hierarchy. It connects a mobile network to the fixed telephone network (the PSTN) and to other operators with which it has roaming agreements. One of its most important roles is to translate the protocol cellular system's own signalling protocols to Signaling System (SS7), the protocol which regular telephone lines use to carry information such as phone numbers

2.2.2 Video

Mobile video telephony is frequently seen as a future strategy - something that will become significant once 3G networks are widely deployed. Video offers, including live video calling, are becoming available on newly deployed 3G networks in Japan, Korea and portions of Europe.

Video clips can easily be included in the range of content available for download. Even on a GPRS network, sending or downloading a five-to-15-second video clip can be completed within 30 to 40 seconds. Multimedia handsets are available, from all major handset vendors.

As MMS (multimedia messaging service) is deployed, video can be included in the range of MMS options. Alternately, e-mail can be used to pass video messages. Again, five-to-15-second video clips are typical with MMS or e-mail, but there is also the option of subscriber-generated content. In other words, just as subscribers use camera phones to take pictures, mobile video handsets allow users to record short video clips. There are interoperable handsets with compatible video capabilities and interconnection for exchanging video messages.

Evolution

There are four video capabilities that support a wide range of video applications. Video download and video messaging using MMS or e-mail are the first; video streaming and live video calling follow.
Video streaming is possible on 2.5G networks, although data rates of 30 kbps to 40 kbps limit content to relatively low resolution and low frame rates. However, this may be adequate for connecting to surveillance cameras in the home or elsewhere. 3G networks support high-performance video streaming, up to and including live TV. The advantage of video streaming is the ability to support arbitrarily long video programs not just 10-second clips. This expands the range of applications to serious news, extended sports coverage, celebrity interviews and so on.

Of course, if the goal is actual broadcast TV, it is more efficient to use broadcast technology than precious mobile phone bandwidth. Combined handsets are now available in Japan that support both 2.5G/3G telephony and broadcast TV reception. Examples are the NEC V601N and the Toshiba V401T.

The ultimate video service is live video calling, video telephony. This requires 3G data rates and a low-latency QoS guarantee. These services are based on the 3G-324M standard. 3G-324M video services get the required QoS by using circuit-switched data, typically at 64 kbps.

Video Applications

The broader view of mobile video includes the range of applications being deployed, tested or proposed, Video on demand and video news alerts. The success of ring tones and logos has led to video phone personalization. There are also video quizzes and games.

Mobile video telephony (two-party calling) has moved beyond trials to widespread day-to-day service. For instance, in Japan, NTT DoCoMo's FOMA (Freedom of Mobile Multimedia Access) service handsets are capable of live video calling.

While the picture quality of this mobile video telephony service is not as great as that of high-end room conferencing systems, mobile video handsets have other advantages. First, they are easy to operate - video and voice work the same way. Second, they are personal and mobile, so there are personal applications that would never appear with a room conferencing system. Business uses include showing field conditions to associates back at the home office.

Although 3G services and high-performance mobile-video applications are in their nascence, the surprise factor is clear. The trend can not be ignored. Fortunately, many video applications can be supported with mobile network.

3.0 CONCLUSION

Mobile communications is more than just a convenience. The evolution of Mobile communication networks obviously has led to innovative technology advancement for instance in mobile service delivery.
Fortunately, the full potential of all the benefits of mobile services we associate with the World Wide Web today - multimedia, e-commerce, unified messaging and peer-to-peer networking will be fulfilled in the future - 4G (Fourth Generation).

4G mobile communications will be based on IP transport, ubiquity and diversity. Open, global and ubiquitous communications make people free from spatial and temporal constraints. Versatile communication systems will also be required to realize customized services based on diverse individual needs. The flexibility of mobile (Information Technology) IT can satisfy these demands simultaneously. Therefore, mobile IT can be seen to play a key fundamental role in the 21st century.

4.0 REFERENCES

A. El-Rabbany, Introduction to GPS : the global positioning system, ISBN 1-58053-183-0, Artech House, 2002

D. Wisely, P. Eardley, L. Burness, IP for 3G Networking Technology for mobile Communication, ISBN 0-471-48697-3, John Wiley & Sons, 2002.

S. NANDA , D.J. GOODMAN, Third generation wireless information networks, ISBN 0-7923-9218-3, Kluwer Academic Pub., 1992

U. Black, Second generation mobile and wireless networks, ISBN 0-13-621277-8, Prentice Hall PTR, 1999