Fiber-Optic Technology

Definition and Overview

Definition

Fiber-optic communications is based on the principle that light in a glass medium can carry more information over longer distances than electrical signals can carry in a copper or coaxial medium. The purity of today's glass fiber, combined with improved system electronics, enables fiber to transmit digitized light signals well beyond 100 km (60 miles) without amplification. With few transmission losses, low interference, and high bandwidth potential, optical fiber is an almost ideal transmission medium.

Overview

The advantages provided by optical fiber systems are the result of a continuous stream of product innovations and process improvements. As the requirements and emerging opportunities of optical fiber systems are better understood, fiber is improved to address them. This tutorial provides an extensive overview of the history, construction, operation, and benefits of optical fiber, with particular emphasis on outside vapor deposition (OVD) process.

1. From Theory to Practical Application: A Quick History

An important principle in physics became the theoretical foundation for optical fiber communications: light in a glass medium can carry more information over longer distances than electrical or radio frequency (RF) signals can carry in a copper, coaxial or wireless medium.

The first challenge undertaken by scientists was to develop a glass so pure that one percent of the light would be retained at the end of one kilometer (km), the existing unrepeatered transmission distance for copper-based telephone systems. In terms of attenuation, this one-percent of light retention translated to 20 decibels per kilometer (dB/km) of glass material.

Glass researchers all over the world worked on the challenge in the 1960s, but the breakthrough came in 1970, when Corning Incorporated scientists Drs. Robert Maurer, Donald Keck, and Peter Schultz created a fiber with a measured attenuation of less than 20 dB per km. It was the purest glass ever made.

The three scientists’ work is recognized as the discovery that led the way to the commercialization of optical fiber technology. Since then, the technology has advanced tremendously in terms of performance, quality, consistency, and applications.

Working closely with customers has made it possible for scientists to understand what modifications are required, to improve the product accordingly through design and manufacturing, and to develop industry-wide standards for fiber.

The commitment to optical fiber technology has spanned more than 30 years and continues today with the endeavor to determine how fiber is currently used and how it can meet the challenges of future applications. As a result of research and development efforts to improve fiber, a high level of glass purity has been achieved. Today, fiber’s optical performance is approaching the theoretical limits of silica-based glass materials. This purity, combined with improved system electronics, enables fiber to transmit digitized light signals hundreds of kilometers without amplification. When compared with early attenuation levels of 20 dB per km, today’s achievable levels of less than 0.35 dB per km at 1310 nanometers (nm) and 0.25 dB per km at 1550 nm, testify to the incredible drive for improvement.

2. How Fiber Works

The operation of an optical fiber is based on the principle of total internal reflection. Light reflects (bounces back) or refracts (alters its direction while penetrating a different medium), depending on the angle at which it strikes a surface.

One way of thinking about this concept is to envision a person looking at a lake. By looking down at a steep angle, the person will see fish, rocks, vegetation, or whatever is below the surface of the water (in a somewhat distorted location due to refraction), assuming that the water is relatively clear and calm. However, by casting a glance farther out, thus making the angle of sight less steep, the individual is likely to see a reflection of trees or other objects on an opposite shore. Because air and water have different indices of refraction, the angle at which a person looks into or across the water influences the image seen.

This principle is at the heart of how optical fiber works. Controlling the angle at which the light waves are transmitted makes it possible to control how efficiently they reach their destination. Lightwaves are guided through the core of the optical fiber in much the same way that radio frequency (RF) signals are guided through coaxial cable. The lightwaves are guided to the other end of the fiber by being reflected within the core.

The composition of the cladding glass relative to the core glass determines the fiber’s ability to reflect light. That reflection is usually caused by creating a higher refractive index in the core of the glass than in the surrounding cladding glass, creating a “waveguide.” The refractive index of the core is increased by slightly modifying the composition of the core glass, generally by adding small amounts of a dopant. Alternatively, the waveguide can be created by reducing the refractive index of the cladding using different dopants.

The Design of Fiber

Core, Cladding, and Coating

An optical fiber consists of two different types of highly pure, solid glass, composed to form the core and cladding. A protective acrylate coating (see Figure 1) then surrounds the cladding. In most cases, the protective coating is a dual layer composition.

Figure 1. Core, Cladding, and Coating

A protective coating is applied to the glass fiber as the final step in the manufacturing process. This coating protects the glass from dust and scratches that can affect fiber strength. This protective coating can be comprised of two layers: a soft inner layer that cushions the fiber and allows the coating to be stripped from the glass mechanically and a harder outer layer that protects the fiber during handling, particularly the cabling, installation, and termination processes.

Single-Mode and Multimode Fibers

There are two general categories of optical fiber: single-mode and multimode (see Figure 2).

Figure 2. Single-Mode and Multimode Fibers

Multimode fiber was the first type of fiber to be commercialized. It has a much larger core than single-mode fiber, allowing hundreds of modes of light to propagate through the fiber simultaneously. Additionally, the larger core diameter of multimode fiber facilitates the use of lower-cost optical transmitters (such as light emitting diodes [LEDs] or vertical cavity surface emitting lasers [VCSELs]) and connectors.

Single-mode fiber, on the other hand, has a much smaller core that allows only one mode of light at a time to propagate through the core. While it might appear that multimode fibers have higher capacity, in fact the opposite is true. Singlemode fibers are designed to maintain spatial and spectral integrity of each optical signal over longer distances, allowing more information to be transmitted.

Its tremendous information-carrying capacity and low intrinsic loss have made single-mode fiber the ideal transmission medium for a multitude of applications. Single-mode fiber is typically used for longer-distance and higher-bandwidth applications (see Figure 3). Multimode fiber is used primarily in systems with short transmission distances (under 2 km), such as premises communications, private data networks, and parallel optic applications.

Optical Fiber Sizes

The international standard for outer cladding diameter of most single-mode optical fibers is 125 microns (µm) for the glass and 245 µm for the coating. This standard is important because it ensures compatibility among connectors, splices, and tools used throughout the industry.

Standard single-mode fibers are manufactured with a small core size, approximately 8 to 10 µm in diameter. Multimode fibers have core sizes of 50 to 62.5 µm in diameter.

Figure 3. Optical Fiber Sizes

3. Outside Vapor Deposition (OVD) Process

Basic OVD optical fiber manufacturing consists of three steps: laydown, consolidation, and draw.

Laydown

In the laydown step, a soot preform is made from ultrapure vapors as they travel through a traversing burner and react in the flame to form fine soot particles of silica and germania (see Figure 4).

Figure 4. OVD Laydown Process

The OVD process is distinguished by the method of depositing the soot. These particles are deposited on the surface of a rotating target rod. The core material is deposited first, followed by the pure silica cladding. As both core and cladding raw materials are vapor-deposited, the entire preform becomes totally synthetic and extremely pure.

Consolidation

When deposition is complete, the bait rod is removed from the center of the porous preform, and the preform is placed into a consolidation furnace. During the consolidation process, the water vapor is removed from the preform. This high-temperature consolidation step sinters the preform into a solid, dense, and transparent glass.

The Draw

The finished glass preform is then placed on a draw tower and drawn into one continuous strand of glass fiber (see Figure 5).

Figure 5. Optical Fiber Drawing Process

First, the glass blank is lowered into the top of the draw furnace. The tip of the blank is heated until a piece of molten glass, called a gob, begins to fall from the blank—much like hot taffy. As the glob falls it pulls behind it a thin strand of glass, the beginning of an optical fiber.

The gob is cut off, and the fine fiber strand is threaded into a computer-controlled tractor assembly and drawn. Then, as the diameter is monitored, the assembly speeds up or slows down to precisely control the size of the fiber’s diameter.

The fiber progresses through a diameter sensor that measures the diameter hundreds of times per second to ensure specified outside diameter. Next, the inner and outer primary coatings are applied and cured, using ultraviolet lamps. At the bottom of the draw, the fiber is wound on spools for further processing.

Fiber from these spools is proof-tested and then measured for performance of relevant optical and geometrical parameters. Each fiber has a unique identification number that can be traced to all relevant manufacturing data (including raw materials and manufacturing equipment). Each fiber reel is then placed into protective shipping containers and prepared for shipment to customers worldwide.

4. OVD Benefits

Fiber produced using the OVD process is purely synthetic, exhibits enhanced reliability, and allows for precise geometrical and optical consistency. The OVD process produces a very consistent “matched-clad” fiber.

OVD fibers are made of a core and cladding glass, each with slightly different compositions. The manufacturing process provides the relationship between these two glasses. A matched-clad, single-mode fiber design allows for a consistent fiber (see Figure 6).

Figure 6. Index Profile of a Matched-Clad Fiber Design

The OVD process produces well-controlled fiber profiles and geometry, both of which lead to a more consistent fiber. Fiber-to-fiber consistency is especially important when fibers from different manufacturing periods are joined, through splicing and connectorization, to form an optical system.

Depressed-Clad Fiber Profile

The modified chemical vapor deposition (MCVD) process produces what is called depressed-clad fiber because of the shape of its refractive index profile.

Figure 7. Index Profile of a Depressed-Clad Fiber Design

Depressed-clad fibers are made with two different cladding glasses that form an inner and an outer cladding region. The outer cladding consists of a glass from a substrate tube that is generally purchased from an outside supplier, as opposed to the OVD method, where all of the glass is made synthetically within the fiber manufacturer’s control. The inner cladding region adjacent to the fiber core has an index of refraction that is lower than that of pure silica, while the outer cladding has an index equal to that of pure silica. Hence, the index of the glass adjacent to the core is depressed.

Questions of Strength

One common misconception about optical fiber is that it must be fragile because it is made of glass. In fact, research, theoretical analysis, and practical experience prove that the opposite is true. While traditional bulk glass is brittle, the ultrapure glass of optical fibers exhibits both high tensile strength and extreme durability.

How strong is fiber? Figures like 600 or 800 thousand pounds per square inch are often cited, far more than copper’s capability of 100 pounds per square inch. That figure refers to the ultimate tensile strength of fiber produced today. Fiber’s real, rather than theoretical, strength is 2 million pounds per square inch.

ABCs of Fiber Strength

The depth of inherent microscopic flaws on its surface determines the actual strength of optical fiber. These microscopic flaws exist in any fiber. As in a length of chain, the weakest link (or, in fiber’s case, the deepest flaw) determines the ultimate strength of the entire length of the chain. The flaws are distributed along the fiber length – the larger the flaw, the more distance between them along the fiber.

Many fiber manufacturers tensile-load, or proof-test, fibers after production. This process eliminates proof-test size flaws and larger, thereby ensuring that the flaws of most concern are removed and creating a minimum design strength for the fiber.

Life Expectancy

Fiber is designed and manufactured to provide a lifetime of service, provided it is cabled and installed according to recommended procedures. Life expectancy can be extrapolated from many tests. These test results, along with theoretical analysis, support the prediction of long service life. Environmental issues are also important to consider when evaluating a fiber’s mechanical and reliability performance.

Bending Parameters

Optical fiber and cable are easy to install because it is lightweight, small in size, and flexible. Nevertheless, precautions are needed to avoid tight bends, which may cause loss of light or premature fiber failure.

Experience and testing show that bare fiber can be safely looped with bend diameters as small as two to three inches, depending on allowable optical loss. Splice trays and other fiber-handling equipment, such as racks, are designed to prevent fiber-installation errors such as this.

5. Fiber Geometry: A Key Factor in Splicing and System Performance

As greater volumes of fiber in higher fiber-count cables are installed, system engineers are becoming increasingly conscious of the impact of splicing on their systems. Splice yields and system losses have a profound impact on the quality of system performance and the cost of installation.

Glass geometry, the physical dimensions of an optical fiber, has been shown to be a primary contributor to splice loss and splice yield in the field. Early on, one company recognized the benefit provided by tightly controlled fiber geometry and has steadily invested in continuous improvement in this area. The manufacturing process helps engineers reduce systems costs and support the industry’s low maximum splice-loss requirement, typically at around 0.1 dB.

Fiber that exhibits tightly controlled geometry tolerances will not only be easier and faster to splice but will also reduce the need for testing by ensuring predictable, high-quality splice performance. This is particularly true when fibers are spliced by passive, mechanical, or fusion techniques for both single fibers and fiber ribbons. In addition, tight geometry tolerances lead to the additional benefit of flexibility in equipment choice.

The benefits of tighter geometry tolerances can be significant. In today’s fiber-intensive architectures, it is estimated that splicing and testing can account for more than 30 percent of the total labor costs of system installation.

Fiber Geometry Parameters

The three fiber geometry parameters that have the greatest impact on splicing performance include the following:

• cladding diameter—the outside diameter of the cladding glass region.
• core/clad concentricity (or core-to-cladding offset)—how well the core is centered in the cladding glass region
• fiber curl—the amount of curvature over a fixed length of fiber

These parameters are determined and controlled during the fiber-manufacturing process. As fiber is cut and spliced according to system needs, it is important to be able to count on consistent geometry along the entire length of the fiber and between fibers and not to rely solely on measurements made.

Cladding Diameter

The cladding diameter tolerance controls the outer diameter of the fiber, with tighter tolerances ensuring that fibers are almost exactly the same size. During splicing, inconsistent cladding diameters can cause cores to misalign where the fibers join, leading to higher splice losses. The drawing process controls cladding diameter tolerance, and depending on the manufacturer’s skill level, can be very tightly controlled.

Core/Clad Concentricity

Tighter core/clad concentricity tolerances help ensure that the fiber core is centered in relation to the cladding. This reduces the chance of ending up with cores that do not match up precisely when two fibers are spliced together. A core that is precisely centered in the fiber yields lower-loss splices more often.

Core/clad concentricity is determined during the first stages of the manufacturing process, when the fiber design and resulting characteristics are created. During these laydown and consolidation processes, the dopant chemicals that make up the fiber must be deposited with precise control and symmetry to maintain consistent core/clad concentricity performance throughout the entire length of fiber.

Fiber Curl

Fiber curl is the inherent curvature along a specific length of optical fiber that is exhibited to some degree by all fibers. It is a result of thermal stresses that occur during the manufacturing process. Therefore, these factors must be rigorously monitored and controlled during fiber manufacture. Tighter fiber-curl tolerances reduce the possibility that fiber cores will be misaligned during splicing, thereby impacting splice loss.

Some mass fusion splicers use fixed v-grooves for fiber alignment, where the effect of fiber curl is most noticeable.

Figure 8. Cladding Diameter, Core/Clad Concentricity, and Fiber Curl

6. How to Choose Optical Fiber

Single-Mode Fiber Performance Characteristics

The key optical performance parameters for single-mode fibers are attenuation, dispersion, and mode-field diameter.

Optical fiber performance parameters can vary significantly among fibers from different manufacturers in ways that can affect your system's performance. It is important to understand how to specify the fiber that best meets system requirements.

Attenuation

Attenuation is the reduction of signal strength or light power over the length of the light-carrying medium. Fiber attenuation is measured in decibels per kilometer (dB/km).

Optical fiber offers superior performance over other transmission media because it combines high bandwidth with low attenuation. This allows signals to be transmitted over longer distances while using fewer regenerators or amplifiers, thus reducing cost and improving signal reliability.

Attenuation of an optical signal varies as a function of wavelength (see Figure 9). Attenuation is very low, as compared to other transmission media (i.e., copper, coaxial cable, etc.), with a typical value of 0.35 dB/km at 1300 nm for standard single-mode fiber. Attenuation at 1550 nm is even lower, with a typical value of 0.25 dB/km. This gives an optical signal, transmitted through fiber, the ability to travel more than 100 km without regeneration or amplification.

Attenuation is caused by several different factors, but primarily scattering and absorption. The scattering of light from molecular level irregularities in the glass structure leads to the general shape of the attenuation curve (see Figure 9). Further attenuation is caused by light absorbed by residual materials, such as metals or water ions, within the fiber core and inner cladding. It is these water ions that cause the “water peak” region on the attenuation curve, typically around 1383 nm. The removal of water ions is of particular interest to fiber manufacturers as this “water peak” region has a broadening effect and contributes to attenuation loss for nearby wavelengths. Some manufacturers now offer low water peak single-mode fibers, which offer additional bandwidth and flexibility compared with standard single-mode fibers. Light leakage due to bending, splices, connectors, or other outside forces are other factors resulting in attenuation.

Figure 9. Typical Attenuation vs. Wavelength

Dispersion

Dispersion is the time distortion of an optical signal that results from the time of flight differences of different components of that signal, typically resulting in pulse broadening (see Figure 10). In digital transmission, dispersion limits the maximum data rate, the maximum distance, or the information-carrying capacity of a single-mode fiber link. In analog transmission, dispersion can cause a waveform to become significantly distorted and can result in unacceptable levels of composite second-order distortion (CSO).

Figure 10. Impact of Dispersion

Dispersion vs. Wavelength

Single-mode fiber dispersion varies with wavelength and is controlled by fiber design (see Figure 11). The wavelength at which dispersion equals zero is called the zero-dispersion wavelength (λ _º ). This is the wavelength at which fiber has its maximum information-carrying capacity. For standard single-mode fibers, this is in the region of 1310 nm. The units for dispersion are also shown in Figure 11.

Figure 11. Typical Dispersion vs. Wavelength Curve

Chromatic dispersion consists of two kinds of dispersion. Material dispersion refers to the pulse spreading caused by the specific composition of the glass. Waveguide dispersion results from the light traveling in both the core and the inner cladding glasses at the same time but at slightly different speeds. The two types can be balanced to produce a wavelength of zero dispersion anywhere within the 1310 nm to 1650 nm operating window.

Transmission in the 1550 nm Window

Optical fibers also can be manufactured to have low dispersion wavelength in the 1550-nm region, which is also the point where silica-based fibers have inherently minimal attenuation. These fibers are referred to as dispersion-shifted fibers and are used in long-distance applications with high bit rates. For applications utilizing multiple wavelengths, it is undesirable to have the zero dispersion point within the operating wavelength range and fibers known as non-zero dispersion-shifted fiber (NZ-DSF) are most applicable. NZ-DSF fibers with large effective areas are used to obtain greate capacity transmission over longer distance than would be possible with standard single-mode fibers. These fibers are able to take advantage of the optical amplifier technology available in the 1530 to 1600+ nm operating window while mitigating nonlinear effect, as that can be troublesome at higher power levels.

For applications such as the interconnectino of headends, delivery of programming to remote node sites, high-speed communication networks, and regional and metropolitan rings (used primarily for competitive access applications), NZDSF fiber can improve system reliability, increase capacity, and lower system costs.

Mode-Field Diameter

Mode-field diameter (MFD) describes the size of the light-carrying portion of the fiber. For single-mode fibers, this region includes the fiber core as well as a small portion of the surrounding cladding glass. MFD is an important parameter for determining a fiber’s resistance to bend-induced loss and can affect splice loss as well. MFD, rather than core diameter, is the functional parameter that determines optical performance when a fiber is coupled to a light source, connectorized, spliced, or bent. It is a function of wavelength, core diameter, and the refractive-index difference between the core and the cladding. These last two are fiber design and manufacturing parameters.

Cutoff Wavelength

Cutoff wavelength is the wavelength above which a single-mode fiber supports and propagates only one mode of light. An optical fiber that is single-moded at a particular wavelength may have two or more modes at wavelengths lower than the cutoff wavelength.

The effective cutoff wavelength of a fiber is dependent on the length of fiber and its deployment and the longer the fiber, the lower the effective cutoff wavelength. Or the smaller the bend radius of a loop of the fiber is, the lower the effective cutoff wavelength will be. If a fiber is bent in a loop, the cutoff is lowered. The cutoff wavelength of a fiber is reduced when it is cabled. The reduction is predictable, enough so that fiber manufacturers can specify a maximum “cable cutoff wavelength” for the fiber.

Environmental Performance

While cable design and construction play a key role in environmental performance, optimum system performance requires the user to specify fiber that will operate without undue loss from microbending.

Microbends are small-scale perturbations along the fiber axis, the amplitude of which are on the order of microns. These distortions can cause light to leak out of a fiber. Microbending may be induced at very cold temperatures because the glass has a different coefficient of thermal expansion from the coating and cabling materials. At low temperatures, the coating and cable become more rigid on the glass to cause microbends. Coating and cabling materials are selected by manufacturers to minimize loss due to microbending.

Specification Examples of Uncabled Fiber

To ensure that a cabled fiber provides the best performance for a specific application, it is important to work with an optical fiber cable supplier to specify the fiber parameters just reviewed as well as the geometric characteristics that provide the consistency necessary for acceptable splicing and connectorizing.

Splicers and Connectors

As optical fiber moves closer to the customer, where cable lengths are shorter and cables have higher fiber counts, the need for joining fibers becomes greater. Splicing and connectorizing play a critical role both in the cost of installation and in system performance.

The object of splicing and connectorizing is to precisely match the core of one optical fiber with that of another in order to produce a smooth junction through which light signals can continue without alteration or interruption. There are two ways that fibers are joined:

• splices, which form permanent connections between fibers in the system
• connectors, which provide remateable connections, typically at termination points

Fusion Splicing

Fusion splicing provides a fast, reliable, low-loss, fiber-to-fiber connection by creating a homogenous joint between the two fiber ends. The fibers are melted or fused together by heating the fiber ends, typically using an electric arc. Fusion splices provide a high-quality joint with the lowest loss (in the range of 0.01 dB to 0.10 dB for single-mode fibers) and are practically nonreflective.

Mechanical Splicing

Mechanical splicing is an alternative method of making a permanent connection between fibers. In the past, the disadvantages of mechanical splicing have been slightly higher losses, less-reliable performance, and a cost associated with each splice. However, advances in the technology have significantly improved performance. System operators typically use mechanical splicing for emergency restoration because it is fast, inexpensive, and easy. (Mechanical splice losses typically range from 0.05.0.2 dB for single-mode fiber.)

Connectors

Connectors are used in applications where flexibility is required in routing an optical signal from lasers to receivers, wherever reconfiguration is necessary, and in terminating cables. These remateable connections simplify system reconfigurations to meet changing customer requirements.

Acronyms Guide

CNR - carrier-to-noise ratio

CSO - composite second-order distortion

IVD - inside vapor deposition

MCVD - modified chemical vapor deposition

MFD - mode-field diameter

NZDSF - nonzero dispersion-shifted fiber

Billing in a 3G Environment

Definition and Overview

Definition
Billing in a 3G environment refers to the capacity of a wireless communications service provider to capture, rate, and bill next-generation mobile communications events. These events include voice, data, and electronic content such as mobile Web browsing and e-mail, mobile commerce activities, and streaming video.

Overview
The migration from second generation (2G) to third generation (3G) wireless communications systems represents a landmark shift in the development of the mobile communications industry—and the communications and information industries in general.

This tutorial explores the evolution of the wireless market from 2G through interim 2.5G to advanced 3G networks. Its central focus is an examination of the challenges that service providers face in deploying billing systems that are capable of meeting existing requirements and flexible enough to support the gradual adoption of 2.5G and 3G next-generation services by consumers.

The tutorial also reviews the enabling technologies and standards that define each generation of communications services. To satisfy the unique billing requirements of carriers that deploy advanced network services, billing systems must support the standards described in the following sections.

1. 2G Billing Challenges

The introduction of 2G cellular radio in the 1990s led to a genuine and significant change in human behavior. Technically, it provided the basis for the transition of voice technology from an analog, wired environment to a digital, wireless environment. Psychologically and socially, the advent of 2G transformed telecommunications from a communications tool to an agent of social change that improved people's professional and personal lives by enabling unprecedented communications flexibility.

Deploying a billing system for wireless services has never been simple. However, in the early days of 2G, billing was based on voice minutes. As a result, many wireless carriers, familiar with traditional voice telephony, implemented wireless billing systems using previous models that billed for voice minutes using call detail records (CDR).

2. Transitioning from 2G to 2.5G Network Services

By the late 1990s, wireless subscribers' voracious appetites for value-added services such as two-way messaging, unified communications, electronic voice-mail and e-mail, and personal number services drove an evolution toward more sophisticated 2.5G network services.

The rate of acceptance of 2.5G services varied around the world. The growth of value-added services in the United States was outpaced by widespread acceptance in Europe and Asia. One major reason for this was a lack of integration among various network technologies such as code division multiple access (CDMA), time division multiple access (TDMA), and the Global System for Mobile Communications (GSM). Billing systems could not support the disparate standards required for different network types.

In Europe and Asia, however, the adoption of a single standard, GSM, facilitated rapid acceptance and implementation of value-added 2.5G services.

As a result of the lack of uniformity in standards, wireless carriers focused on two leading criteria in the selection of wireless billing systems:

• Speed to market
• The ability to interface with other systems

These market conditions also gave rise to a new market driver that would confer an important strategic edge—convergence—the ability to offer and bill for multiple services, such as long distance, Web browsing, and voice on a single bill. Convergence prompted wireless carriers to plan the rollout of enhanced services and products that would extend wireless capabilities well beyond voice.

By 1998, wireless messaging had gained a foothold in Asia. Mixed mobile and fixed services, as well as value-added services, enjoyed growing popularity in Latin America. Meanwhile, in more mature markets such as the United Kingdom, the United States, and parts of Europe, increasing numbers of carriers began upgrading their billing systems to support the growing market for wireless data offerings.

The rollout of these services presented a critical challenge. To offer wireless data services, carriers needed a billing system that could accommodate the new services—particularly if charges were to be calculated based on the quantity of data transferred rather than the duration of time on-line.

As a result, convergent services strained legacy billing systems that were designed to measure and rate usage-sensitive wireless voice. With the emergence of 2.5G, existing billing systems simply were not equipped to rate wireless data, which typically was charged based on a flat rate.

3. The Emergence of 2.5G Services and Resulting Billing Challenges

Mobile data technologies such as short message service (SMS), wireless application protocol (WAP), and general packet-switched radio service (GPRS) have facilitated the move into the 2.5G world of content, with applications such as mobile e-mail and access to other Web-based services via mobile handsets.

SMS originated as a platform for e-mail and value-added services such as news, weather, and stock reports. WAP, which allows Internet content to be retrieved via mobile phones or other wireless devices, became available to the mass market in 2000.

Concurrent with the introduction of WAP, GPRS facilitates GSM–based wireless broadband access to the Internet via a personal computer (PC). GPRS also enhances WAP service levels. GPRS enables mobile service providers to offer complex services that are transferred as packet-switched, non-voice, value-added services. This is in contrast to traditional circuit-switched services that are available across mobile networks.

GPRS adds value because it enables instant wireless connections ("always on" service), which in turn allow information to be sent or received immediately as the need arises, subject to radio coverage. No dial-up modem connection is necessary.

Despite the accelerated pace of development in wireless technology and the digital data world, business drivers have focused on acquiring customers and increasing revenue to the exclusion of developing and implementing adequate billing and business solutions. Consequently, many entrants into the 2.5G marketplace had to rely on less-than-adequate billing solutions, using shortcuts to accommodate the drivers. Two of the most common shortcuts include the following:

• Bundling data charges into access charges
• Adding "all-you-can-eat" service for a flat rate

In assessing the complexity of billing for wireless data, the first challenge has been event collection and mediation. Carriers needed to deploy Internet protocol (IP) billing models capable of capturing information from multiple servers, routers, gateways, and content providers.

Suddenly, as service providers watched their margins disappear, flat-rate billing began to lose its appeal. The new catch phrase used to describe more recent usage-sensitive billing is billing for content. This new billing model is currently being addressed by billing standards organizations such as the Global Billing Association (GBA) to represent industry interests.

The objective of billing for content is two-fold—to help all service providers, and mobile service providers in particular, to determine the following:

• The type of data being transmitted over their networks
• How to capture revenue from the data being transmitted

As the rollout of more sophisticated and complex 3G services becomes a reality, these questions present an even greater challenge.

4. Next-Generation 3G Services: Bringing Challenge and Opportunity

In the future, as 3G services are adopted, GPRS will provide a massive boost to mobile data usage and usefulness. The promise of next-generation technology is likely to be realized because of its flexible feature set, and inherent latency, efficiency, and speed.

In Europe, next-generation or 3G cellular mobile radio is known as Universal Mobile Telecommunications System (UMTS). UMTS is expected to offer broadband multimedia services in addition to basic services such as voice.

Both GPRS and UMTS will support many new types of services. These include the following:

• Streaming video services
• Videoconferencing
• Interactive on-line shopping
• Location-sensitive directories
• On-line banking, stock trading, and sports reporting

It is unlikely that these services initially will justify the significant capital investment required to fund the network development that enables them. Instead, industrial and commercial applications will most likely lead the way as major consumers of pure bandwidth.

The types of commercial applications being proposed include expanded versions of existing sales and service applications—extending on-line computer facilities to staff in the field and using mobile security applications to monitor buildings and moving vehicles.

If the mobile Internet is to succeed and enjoy widespread acceptance, service providers must offer a variety of services. However, service providers alone cannot supply all of the services that consumers will require. In fact, growth would be severely hampered if service offerings were limited to only those that service providers can develop and offer. As a result, in addition to their own, service providers will have to offer services supplied by outside sources.

Service-Provider Challenges

While the possibilities that result from the launch of next-generation services and content-based services are exciting, they present service providers with numerous challenges, such as the following:

• Where to assess the value of the content moving across networks
• How to deliver content developed and provided by third parties
• How to capture revenue generated by content provided by outside sources

Service-Provider Advantages

As service providers scramble to establish effective models for billing for these new services, several factors work in their favor:

• Service providers already interface with subscribers on a monthly basis in the form of invoices
• Service providers can bill content providers, uniquely positioning them as aggregators of content

Redefining Billing Requirements to Keep Pace With Change

As described previously, GPRS and UMTS are packet-switched networks that will change the elements of billing for a number of reasons:

• Users will be able to access content via a visual subscriber interface—as opposed to voice, mobile subscribers will be able to send and receive text, pictures, and video.

• New users will always be on-line. The concept of "making a call" will disappear.

• Networks will be able to locate users within a few miles or meters. This capability yields new forms of advertising and sponsored services, which means that third parties may be prepared to pay operators for access to their subscribers.

• To support GPRS and UMTS services, a new generation of mobile "phone" is being developed. The lines between traditional phones and laptops will blur as technologies converge. Different types of consumers will use different types of devices, depending on whether they want games, music, video, or voice.

• New partnership opportunities will abound as communications service providers partner with outside sources to produce the content that they cannot produce in-house. As a result, the volume of settlement activities required to manage the exchange of content between networks is expected to grow. Depending on the length of the value-chain, the speed with which the settlements are made will become critical.

• New, next-generation networks will generate different forms of data using different types of records in larger quantities. Forecasts range from twice as much data to 50 or even 100 times as much. Scalability in a billing system will be imperative.

Diagram of 3G Billing System

5. New Business Models for Billing 3G Services

In view of the new services and resulting billing challenges, the overriding question is how should these new services be billed? Data and content-based services enabled by high-bandwidth packet networks will require new business models. Consequently, service providers will have to modify or replace existing, voice-centric billing infrastructures with new systems.

Devising a Framework for Next-Generation Billing Systems

To be viable, next-generation billing systems must be capable of pricing data and content events in addition to voice calls. They will have to be highly flexible, event-based, and truly convergent. In developing a billing solution equal to the task, a number of new parameters for calculating charges can be used:

• Number of packets
• Uploading or downloading of data
• Quality of service (QoS)
• Location
• Content

Communication service providers will certainly seek to bill subscribers directly for some services. However, they may also consider any of the following scenarios:

• Billing third parties for access to subscribers: Banks, travel agents, stock-brokers and similar entities could be billed for secure access to mobile subscribers.

• Billing subscribers directly for everything, including content: This scenario would generate a convergent bill that resembles a credit card statement, giving the service provider complete control of the relationship and maximizing the value of the customer relationship. This model would require a complex system to track the delivery of goods, ensure the QoS across the various forms of content that they deliver, and settle payments with suppliers.

• Billing content providers for access: Subscribers might pay content providers directly and service providers might receive a commission. This type of approach would simplify logistics for the operator, but also would burden the subscriber with multiple bills.

Keys Issues in Selecting a 3G Billing System

When it comes to selecting a billing system, a number of key issues must be considered. The right billing system must do the following:

• Be real-time. To perform balance management and authorization for 3G services, the billing system must return a price for an ordered good or service in a sub-second time frame.

• Be based on open industry standards to allow for interoperability with other OSS solutions

• Be modular to minimize total cost of ownership (TCO) for the communications service providers

• Accommodate all current and future types of services (including voice, data, and content)

• Support bundling of these services into cross-product packages to meet the needs of individual market segments

• Provide a "customer-centric view" of the account versus a "service-centric view." This means that the customer-service representative (CSR) has a 360-degree view of the customer with all his or her services in order to give targeted and relevant service.

• Minimize time to market for new products and services. State-of-the-art billing systems are not an obstacle anymore when it comes to launching new products—they are essential tools.

• Enable the customer to perform his or her own customer care via the Web or any other device (WAP phone, handheld, etc.)

6. Conclusion

Criteria like these are important factors to consider when evaluating and making decisions about potential billing solutions in the 3G environment. In the best of all worlds, an ideal solution will address all of these requirements. However, as the nature of services is redefined, certain compromises will be necessary. For example, the sheer complexity of service offerings will make fully itemized bills impractical. At the same time, self-care will enable users to examine their bills in the detail of their choice. In all cases, the bill must be clear and easy to decipher.

In weighing the pros and cons of the respective billing approaches, one fact is clear. The common denominator is the need for a technically practical way to bill for services—one that makes sense to the subscriber.

Service providers must approach GPRS and UMTS services in a consistent and straightforward manner and should bill subscribers in the same ways that they would be billed for the traditional version of the service.

As the GPRS and UMTS communications "revolution" unfolds, promising extraordinary changes in the ways in which we communicate, exchange information, and make purchases, no one knows exactly what the future will bring.

What we do know is that the future will not be exactly what we expect it to be. And we know that it is reasonable to expect that the business models that will succeed are those that can evolve over time.

In conclusion, billing systems must be as flexible as possible. And because service providers cannot be tied down to particular ways of doing business, they will have to forge alliances with business partners that are just as flexible and adaptable.

Compared to the considerable capital investment that service providers are making in GPRS and UMTS services, the customer care and billing investment is a relatively small one. It is, however, a central and vital concern in a marketplace where differentiation is the key to success.

A leading determinant in market differentiation will be the customer-care and billing system—and in some cases, it may be the pivotal investment that will mean the difference between success and failure.

Glossary

Bill Cycle
The period for which a consumer receives an invoice; can also denote when a cycle begins or ends

Call Detail Record (CDR)
A billing-system feature that tracks details about calls, such as type, time, duration, originator, and destination. CDRs can be used for network monitoring, accounting, and billing purposes.

Carrier
(1) A telecommunication company that offers its services to the public; typically, a carrier files tariffs that are equally applied to all consumers; (2) a continuously varying electromagnetic signal that carries analog signals such as frequency modulation (FM), amplitude modulation (AM), or digital signals. (AKA: service provider, operator)

Cellular Telecommunications Industry Association (CTIA)
A trade organization that represents the cellular/PCS wireless industry and is involved with regulatory and public affairs issues in the mobile wireless phone industry

Code Division Multiple Access (CDMA)
CDMA is a generic term that describes a wireless air interface based on code division multiple access technology.

cdmaOne™ is a brand name, trademarked and reserved for the exclusive use of CDG member companies, that describes a complete wireless system that incorporates the interim standard (IS)–95 CDMA air interface, the American National Standards Institute (ANSI)–41 network standard for switch interconnection, and many other standards that make up a complete wireless system. CDMA2000 is a name identifying the 3G technology that is an evolutionary outgrowth of cdmaOne offering operators that have deployed a 2G cdmaOne system—a seamless migration path that economically supports an upgrade to 3G features and services within existing spectrum allocations for both cellular and personal communications system (PCS) operators. CDMA2000 supports the 2G network aspect of all existing operators regardless of technology (cdmaOne, IS–136 TDMA, or GSM). This standard is also known by its International Telecommunication Union (ITU) name International Mobile Telecommunications (IMT)–CDMA Multi-Carrier (1X/3X).

Convergence
The ability to offer and bill for multiple services

Customer-Service Representative (CSR)
A carrier representative who deals with the consumer for ordering services and handling troubles or discrepancies in billing records

Event Processing
The process of gathering events in a network for the purposes of billing and/or network monitoring. Most often associated with capturing the details of 2.5 and 3G services such as short message service, mobile Web browsing, mobile e-mail, and multimedia.

General Packet Radio Service (GPRS)
A GSM data transmission technique that does not set up a continuous channel from a portable terminal for the transmission and reception of data, but transmits and receives data in packets. It makes very efficient use of available radio spectrum, and users pay only for the volume of data sent and received.

Global Positioning System (GPS)
A series of 24 geosynchronous satellites that continuously transmit their position. Used in personal tracking, navigation, and automatic vehicle-location technologies.

Global System for Mobile Communications (GSM)
A digital cellular or PCS network used throughout the world

Internet Protocol Detail Record (IPDR)
IPDR.org is an open consortium of leading companies working together to bring this vision to reality. Collaborating service providers, equipment vendors, system integrators, and billing and mediation vendors facilitate the exchange of usage and control data between network and hosting elements and operations and business support systems by the deployment of IPDR standards.

Mediation Device
A device that can interface with complex multivendor switches and billing systems to gather the required information for provisioning; also can refer to the software used by carriers to interconnect operations support systems (OSS).

Personal Communications Service (PCS)
A two-way, 1900 MHz digital voice, messaging, and data service designed as the second generation of cellular.

Personal Digital Assistant (PDA)
A portable computing device capable of transmitting data. These devices make possible services such as paging, data messaging, electronic mail, computing, facsimile, date books, and other information-handling capabilities.

Provisioning
The process by which a requested service is designed, implemented, and tracked for a particular customer.

Quality of Service (QoS)
A measure of a carrier's service to a consumer

Rate Plan
The plan to which a consumer agrees upon requesting service

Time Division Multiple Access (TDMA)
A method of digital wireless communications transmission allowing a large number of users to access (in sequence) a single radio frequency channel without interference by allocating unique time slots to each user within each channel

Universal Mobile Telecommunications System (UMTS)
Europe's approach to standardization for 3G cellular systems

Web Hosting

Definition and Overview

Definition
The World Wide Web (WWW), a web of worldwide servers connected to the Internet, provides an easily used and understood method of accessing electronic content. Accessing information requires data communication between a Web-browser client and a Web-server application. Web hosting, then, is a means of hosting the Web-server application on a computer system through which electronic content on the Internet is readily available to any Web-browser client.

Overview
This tutorial will provide a basic overview of the main components that enable the Web, present two basic methods of Web hosting known as dedicated and shared, and discuss the challenges of resource management.

1. Overview of the Web

In late 1990 while working at CERN, the European Laboratory for Particle Physics Research in Geneva, Switzerland, Tim Berners-Lee invented the Web, including the definitions of universal resource locator (URL), hypertext transfer protocol (HTTP), and hypertext markup language (HTML). The Web provides a method for easily linking content contained on computer systems distributed throughout the world and connected to the Internet. Utilizing the Web, content on servers from many locations can be seamlessly linked and presented as a comprehensive resource collection. The Web further strengthens the power of the Internet's foundation of distributed computing.

The Web and the Internet remained the world's best-hidden resource until 1993 when Marc Andreessen, an undergraduate at the University of Illinois in Champaign, and a team at the National Center for Supercomputing Applications (NCSA) created the NCSA Mosaic browser. The NCSA Mosaic browser was the first Web-browser client that provided a friendly, point-and-click method for navigating the Internet using the Web.

The invention of the NCSA Mosaic browser was the start of the unprecedented growth of Internet users, Internet service providers (ISPs), and Internet business opportunities. By means of a user-friendly approach to searching and viewing the vast amount of information on the Internet, the Web-browser client enabled nontechnical individuals to benefit from the power and resources of the Internet.

Accessing content through the Web consists of communication between a Web-browser client and a Web server utilizing HTTP (see Figure 1).

Figure 1. Web Overview

The following is a step-by-step description of the communication path, as shown in Figure 1. It assumes that the Web server, the primary domain naming system (DNS) server, and the client computer are connected to the Internet and that all communication is conducted through the Internet.

• steps 1 and 2—The end-user types a URL into the Web browser. The client computer finds the Internet protocol (IP) number associated with the domain name in the URL from the primary DNS server.
• steps 3 and 4—The client computer uses the IP number obtained from the primary DNS server to request, through HTTP, the default HTML file from the Web server associated with the URL. The Web server sends the default HTML file to the client computer. The default HTML file provides information to the client computer for requesting all associated files—such as graphics—for the Web site's complete home page.

When the client computer and Web browser request and receive files from the same URL, the client computer is not required to perform a DNS lookup as described in steps 1 and 2. When the client computer attempts to retrieve a Web site from a different URL, the client computer must then perform steps 1 and 2 again.

2. Overview of Web Hosting

The complex web of servers consists of computer systems installed with Web-server software and connected to the Internet. These servers can be found in any facility with Internet connectivity. The process of maintaining and operating one of these servers is called Web hosting. Web hosting can be conducted in-house by the owner of the Web site, or it can be outsourced to a Web presence provider (WPP).

WPPs are typically companies with one or more data-center facilities that are connected to the Internet. Web hosting provided by WPPs can vary widely with respect to service quality and cost. Some providers consist simply of a room in the basement of a house and a tier-1 (T1) line connected to the local ISP. Others, however, are corporations with state-of-the-art hosting centers consisting of redundant fiber paths for high-speed Internet connections, redundant electrical power sources, a dry pipe–fire suppression system, and an experienced operations group, available 24 hours a day, seven days a week.

Web hosting can be provided on a shared computer environment or on a dedicated computer system. When a Web site consists only of standard HTML code and receives a small number of visitors, shared hosting service is the best solution. When a Web site consists of complex common gateway interface (CGI) scripts and proprietary programs and receives a large number of visitors, dedicated hosting service is the best solution.

3. Web-Hosting Implementation on a Dedicated Platform

The basic concept of Web hosting on a dedicated computer system consists of hosting one Web site on one computer system. The dedicated environment offers complete flexibility and security to both the WPP and the customer.

Web hosting on a dedicated computer system is the simplest and most straightforward method of operating a Web site. Because the computer system contains only one Web site, the configuration of software is standardized, as outlined in the software-installation documentation. Furthermore, system resources are dedicated to only one Web site and, therefore, are not constrained by any other process not associated with the operations of that site.

The essential components of Web hosting on a dedicated computer system are as follows (see Figure 2):

• computer system hardware
• operating system (including transfer control protocol [TCP]/Internet protocol [IP] stack)
• Internet connection (IP number and domain name)
• Web server software (HTTP)

Figure 2. Dedicated Hosting Basic Elements

Additional software applications can be added to the computer system to enhance the Web site and to simplify the process of uploading content. One of these applications is a file transfer protocol (FTP) server for remote access to the computer system for transferring HTML content files.

4. Web-Hosting Implementation on a Shared Platform

The basic concept of Web hosting on a shared computer environment consists of hosting many different Web sites on one computer system. The shared environment offers economic benefits to both the WPP and the customer. Because the Web-hosting environment is the same for all customers, the provider gains economic benefits from allocating portions of the total cost of the hardware, software, maintenance and operation, and customer support amongst all customers. Therefore, the total fixed cost is less on a per-customer basis than with dedicated hosting. The customer gains economic benefit by the reduced price of the Web-hosting service.

The essential components of Web hosting on a shared computer environment are the same as with dedicated hosting, except for the configuration of the software and the management of system resources. There are two basic ways to configure Web-server software for multiple Web sites. The first method is to configure the Web server with each Web site's specific configuration information. The second method is to operate multiple Web-server software on a single computer environment. The first method—a single configuration file with all of the Web site's information—has greater scalability but does not provide a means of limiting the resources consumed by each Web site. Therefore, a combination of both methods is ideal for creating a scalable shared-hosting service. A combination is achieved by using the single configuration file method for Web sites requiring small amounts of resources and using the multiple Web-server method to limit the resources consumed by Web sites that demand large amounts of resources.

When a Web site demands large amounts of system resources, the logical next step is to move the Web site to a dedicated computer system (i.e., dedicated hosting).

5. Web Hosting–Resource Management Challenges

Managing computer-system resources in the shared platform and the dedicated platform is challenging. As a Web site becomes more popular and is sought after by millions of Internet users, the Web site demands more and more system resources. Being able to measure, monitor, and manage the amount of system resources is essential for Web-site availability and server performance.

Critical system resources to manage include the following:

• central processing unit (CPU) utilization
• memory utilization
• disk-swap space
• disk space
• disk input and output
• network input and output
• Internet bandwidth (not a computer-system resource but still requires monitoring and managing)

These critical system resources have a direct relationship with the performance of a specific Web site. A Web site can be created or modified to minimize the demand on these system resources. Some Web sites are developed without the consideration of system-resource utilization. When a Web site contains and executes a common gateway interface CGI script, CPU resources are demanded. If the Web site contains a large number of CGI scripts and requires these scripts to be executed by every Web-site visitor, then CPU resources become a major bottleneck and cause the Web site to appear slow. It is important for the Web-site designer and developer to balance system-resource demands with Web-site functionality and creativity.

To measure, monitor, and manage the computer-system resources, additional software must be installed on the computer system. Each type of computer system hardware requires specific software for resource management. The computer-system manufacturer and operating system–software developer should be able to identify the necessary software applications for measuring, monitoring, and managing the system resources for their specific computer systems.

6. Advanced Web-Hosting Methods

During the last several years, Web hosting has evolved from simple one-computer system architectures to redundant, load-balanced server farms. A server farm is a network of computer systems. As a Web site demands more and more system resources, the traditional hosting environment is constrained by the limited amount of available resources. There are two basic means of providing more resources: a larger computer system or a distributed computer environment. To provide redundancy and scalability, the distributed computer environment is the preferred method of expanding system resources.

The simplest distributed computer environment consists of two identical Web servers on the same local-area network (LAN) with a load-balancing device (see Figure 3). The load-balancing device is the gateway for all traffic entering and leaving the Web servers. The load balancer directs the incoming traffic to the best performing Web server, to alleviate all resource bottlenecks. With the load balancer as the gateway, the two Web servers appear as one large computing environment to all end-users on the Internet. This simple distributed computer environment can be expanded to accommodate more Web servers, providing greater scalability and consistently high performance levels.

Figure 3. Load Balancing Two Web Servers

The simple distributed-computer environment provides a method for increasing the available computer-system resources, but it will not prevent performance problems associated with specific network issues within the LAN or with the Internet connection at that specific location. To overcome local network problems, Web hosting has continued to evolve into a geographically distributed computing–environment architecture.

By distributing the traffic of a Web site across multiple servers located in dispersed geographic locations, system resources can be added without interruptions in the Web-hosting service, and the Web site can always be available despite LAN or Internet-connection problems. Moreover, with intelligent wide-area network (WAN) load balancing, Web-site performance will increase for all visitors, regardless of their geographic location.

Figure 4 illustrates Web hosting in a geographically distributed computing environment.

Figure 4. Two Site Architectures

Glossary

CGI
common gateway interface

DNS
domain naming system

FTP
file transfer protocol

HTML
hypertext markup language

HTTP
hypertext transfer protocol

SSL
secure socket layer

URL
uniform resource locator

Wireless Short Message Service (SMS)

Definition and Overview

Definition
Short message service (SMS) is a globally accepted wireless service that enables the transmission of alphanumeric messages between mobile subscribers and external systems such as electronic mail, paging, and voice-mail systems.

Overview
This tutorial provides an introduction to basic SMS concepts, specifications, networks, and services.

1. Introduction

SMS appeared on the wireless scene in 1991 in Europe. The European standard for digital wireless, now known as the Global System for Mobile Communications (GSM), included short messaging services from the outset.

In North America, SMS was made available initially on digital wireless networks built by early pioneers such as BellSouth Mobility, PrimeCo, and Nextel, among others. These digital wireless networks are based on GSM, code division multiple access (CDMA), and time division multiple access (TDMA) standards.

Network consolidation from mergers and acquisitions has resulted in large wireless networks having nationwide or international coverage and sometimes supporting more than one wireless technology. This new class of service providers demands network-grade products that can easily provide a uniform solution, enable ease of operation and administration, and accommodate existing subscriber capacity, message throughput, future growth, and services reliably. Short messaging service center (SMSC) solutions based on an intelligent network (IN) approach are well suited to satisfy these requirements, while adding all the benefits of IN implementations.

Figure 1 represents the basic network architecture for an IS–41 SMSC deployment handling multiple input sources, including a voice-mail system (VMS), Web-based messaging, e-mail integration, and other external short message entities (ESMEs). Communication with the wireless network elements such as the home location register (HLR) and mobile switching center (MSC) is achieved through the signal transfer point (STP).

Figure 1. Basic Network Architecture for an SMS Deployment (IS–41)

SMS provides a mechanism for transmitting short messages to and from wireless devices. The service makes use of an SMSC, which acts as a store-and-forward system for short messages. The wireless network provides the mechanisms required to find the destination station(s) and transports short messages between the SMSCs and wireless stations. In contrast to other existing text-message transmission services such as alphanumeric paging, the service elements are designed to provide guaranteed delivery of text messages to the destination. Additionally, SMS supports several input mechanisms that allow interconnection with different message sources and destinations.

A distinguishing characteristic of the service is that an active mobile handset is able to receive or submit a short message at any time, independent of whether a voice or data call is in progress (in some implementations, this may depend on the MSC or SMSC capabilities). SMS also guarantees delivery of the short message by the network. Temporary failures due to unavailable receiving stations are identified, and the short message is stored in the SMSC until the destination device becomes available.

SMS is characterized by out-of-band packet delivery and low-bandwidth message transfer, which results in a highly efficient means for transmitting short bursts of data. Initial applications of SMS focused on eliminating alphanumeric pagers by permitting two-way general-purpose messaging and notification services, primarily for voice mail. As technology and networks evolved, a variety of services have been introduced, including e-mail, fax, and paging integration, interactive banking, information services such as stock quotes, and integration with Internet-based applications. Wireless data applications include downloading of subscriber identity module (SIM) cards for activation, debit, profile-editing purposes, wireless points of sale (POSs), and other field-service applications such as automatic meter reading, remote sensing, and location-based services. Additionally, integration with the Internet spurred the development of Web-based messaging and other interactive applications such as instant messaging, gaming, and chatting.

2. Benefits of SMS

In today's competitive world, differentiation is a significant factor in the success of the service provider. Once the basic services, such as voice telephony, are deployed, SMS provides a powerful vehicle for service differentiation. If the market allows for it, SMS can also represent an additional source of revenue for the service provider.

The benefits of SMS to subscribers center around convenience, flexibility, and seamless integration of messaging services and data access. From this perspective, the primary benefit is the ability to use the handset as an extension of the computer. SMS also eliminates the need for separate devices for messaging because services can be integrated into a single wireless device—the mobile terminal. These benefits normally depend on the applications that the service provider offers. At a minimum, SMS benefits include the following:

• Delivery of notifications and alerts
• Guaranteed message delivery
• Reliable, low-cost communication mechanism for concise information
• Ability to screen messages and return calls in a selective way
• Increased subscriber productivity

More sophisticated functionality provides the following enhanced subscriber benefits:

• Delivery of messages to multiple subscribers at a time
• Ability to receive diverse information
• E-mail generation
• Creation of user groups
• Integration with other data and Internet-based applications

The benefits of SMS to the service provider are as follows:

• Ability to increment average revenue per user (due to increased number of calls on wireless and wireline networks by leveraging the notification capabilities of SMS)
• An alternative to alphanumeric paging services, which may replace or complement an existing paging offer
• Ability to enable wireless data access for corporate users
• New revenue streams resulting from addition of value-added services such as e-mail, voice mail, fax, and Web-based application integration, reminder service, stock and currency quotes, and airline schedules
• Provision of key administrative services such as advice of charge, over-the-air downloading, and over-the-air service provisioning
• Protection of important network resources (such as voice channels), due to SMS’ sparing use of the control and traffic channels
• Notification mechanisms for newer services such as those utilizing wireless application protocol (WAP)

All of these benefits are attainable quickly, with modest incremental cost and short payback periods, which make SMS an attractive investment for service providers.

3. Network Elements and Architecture

The basic network structure of the SMS in an IS–41 network is depicted in Figure 1.

External Short Messaging Entities

An ESME is a device that may receive or send short messages. The short message entity (SME) may be located in the fixed network, a mobile device, or another service center.

• VMS—The VMS is responsible for receiving, storing, and playing voice messages intended for a subscriber that was busy or not available to take a voice call. It is also responsible for sending voice-mail notifications for those subscribers to the SMSC.
• Web—The growth of the Internet has also affected the world of SMS. Therefore, it is almost mandatory to support interconnections to the World Wide Web for the submission of messages and notifications. The increasing number of Internet users has a positive impact on the SMS traffic increment experienced in the last few years.
• E-Mail—Probably the most demanded application of SMS is the ability to deliver e-mail notifications and to support two-way e-mail, using an SMS–compliant terminal. The SMSC must support interconnection to e-mail servers acting as message input/output mechanisms.
• Others—There are several other mechanisms to submit short messages to the SMSC that include, but are not limited to, paging networks, specialized software for PC–based messaging and operator bureaus.

SMSC
SMSC is a combination of hardware and software responsible for the relaying and storing and forwarding of a short message between an SME and mobile device.

The SMSC must have high reliability, subscriber capacity, and message throughput. In addition, the system should be easily scalable to accommodate growing demand for SMS in the network.

Normally, an IN–based solution will allow for a lower entry cost compared to point solutions because it can support other applications on a single hardware platform and share resources, thereby spreading the deployment cost over several services and applications.

Another factor to be considered is the ease of operation and maintenance of the application, as well as the flexibility to activate new services and upgrade to new software releases.

Signal Transfer Point
The STP is a network element normally available on IN deployments that allows IS–41 interconnections over signaling system 7 (SS7) links with multiple network elements.

HLR
The HLR is a database used for permanent storage and management of subscriptions and service profiles. Upon interrogation by the SMSC, the HLR provides the routing information for the indicated subscriber. Also, if the destination station was not available when the message delivery was attempted, the HLR informs the SMSC that the station is now recognized by the mobile network to be accessible, and thus the message can be delivered.

Visitor Location Register (VLR)
The visitor location register is a database that contains temporary information about subscribers homed in one HLR who are roaming into another HLR. This information is needed by the MSC to service visiting subscribers.

MSC
The MSC performs the switching functions of the system and controls calls to and from other telephone and data systems. The MSC will deliver the short message to the specific mobile subscriber through the proper base station.

Air Interface
The air interface is defined in each one of the different wireless technologies (GSM, TDMA, and CDMA). These standards specify how the voice or data signals are transferred from the MSC to the handset and back, as well as the utilization of transmission frequencies, considering the available bandwidth and the system’s capacity constraints.

The Base Station System
All functions related to the transmission of electromagnetic radio signals between the MSC and the mobile devices are performed in the base station (BS). The BS consists of base station controllers (BSCs) and the base transceiver stations (BTSs), also known as cell sites or simply “cells.” The BSC may control one or more BTSs and is in charge of the proper resource assignment when a subscriber moves from one sector of one BTS to another, regardless of whether the next sector lies within the same BTS or in a different one.

The Mobile Device
The mobile device is the wireless terminal capable of receiving and originating short messages. Commonly, these devices have been digital cellular phones, but more recently the application of SMS has been extended to other terminals such as POS, handheld computers, and personal digital assistants (PDAs). The wireless network signaling infrastructure is based on SS7. SMS makes use of the mobile application part (MAP), which defines the methods and mechanisms of communication in wireless networks and employs the services of the SS7 transactional capabilities application part (TCAP). An SMS service layer makes use of the MAP signaling capabilities and enables the transfer of short messages between the peer entities.

The capabilities of the terminal vary depending on the wireless technology supported by the terminal. Some functionality, although defined in the SMS specification for a given wireless technology, may not be fully supported in the terminal, which may represent a limitation in the services that the carrier can provide. This trend, however, is disappearing as service providers’ merger and acquisition activity demands uniform functionality across all the constituents of the parent companies. Also, some manufacturers may include additional functionality, not considered in the specification, attempting to offer a more attractive product for service providers as well as end users. This will be the case more often as service provider continue to incorporate SMS into their revenue-generating and customer-loyalty strategies.

4. Signaling Elements

The MAP layer defines the operations necessary to support SMS. Both American and international standards bodies have defined a MAP layer using the services of the SS7 TCAP. The American standard is published by Telecommunication Industry Association and is referred to as IS–41. The international standard is defined by the European Telecommunications Standards Institute (ETSI) and is referred to as GSM MAP.

The following basic MAP operations are necessary to provide the end-to-end SMS:

• Routing Information Request—Before attempting delivery of a short message, the SMSC must receive routing information to determine the serving MSC for the mobile device at the time of the delivery attempt. This is accomplished by way of an interrogation of the destination handset’s HLR, which is accomplished via the use of the SMSrequest and SendRoutingInfoForShortMsg mechanisms in IS–41 and GSM, respectively.
• Point-to-Point Short Message Delivery—The mechanism provides a means for the SMSC to transfer a short message to the MSC that is serving the addressed mobile device. After the address of said MSC has been obtained from the station’s HLR, the short message delivery operation provides a confirmed delivery service. The operation works in conjunction with the base station subsystem while the message is being forwarded from the MSC to the MS. Therefore, the outcome of the operation comprises either success (such as delivery to the mobile) or failure caused by one of several possible reasons. The point-to-point short message delivery is accomplished via the use of the short message delivery–point-to-point (SMD–PP) and forwardShortMessage mechanisms in IS–41 and GSM, respectively.
• Short Message Waiting Indication—he operation is activated when a short message delivery attempt by the SMSC fails due to a temporary failure, such as the station being unregistered, and provides a means for the SMSC to request the HLR to notify the SMSC when the indicated mobile device becomes available. This short message waiting indication is realized via the use of the SMS_notification indicator and set_message_waiting_data mechanisms in IS–41 and GSM, respectively.
• Service Center Alert—The operation provides a means for the HLR to inform the SMSC, which has requested a notification that a specific mobile device is now recognized by the mobile network to be available. This service center alert is accomplished via the use of the SMS_notification and alert_service_center mechanisms in IS–41 and GSM, respectively.

Service Elements
SMS is comprised of several service elements relevant to the reception and submission of short messages:

• Message Expiration—The SMSC will store and reattempt delivery of messages for unavailable recipients until either the delivery is successful or the expiration time—set on a per-message basis or on a platform-wide basis—arrives.
• Priority—This is the information element provided by an SME to indicate the urgent messages and differentiate them from the normal priority messages. Urgent messages usually take priority over normal messages, regardless of the time of arrival to the SMSC platform.
• Message Escalation—The SMSC stores the message for a period no longer than the expiration time (it is assumed that the escalation time is smaller than the expiration time associated with the message), and after said escalation time expires, the message will be sent to an alternate message system (such as a paging network or an e-mail server) for delivery to the user.

In addition, SMS provides a time stamp reporting the time of submission of the message to the SMSC and an indication to the handset of whether or not there are more messages to send (GSM) or the number of additional messages to send (IS–41).

Subscriber Services
SMS comprises two basic point-to-point services:

• Mobile-originated short message (MO–SM)
• Mobile-terminated short message (MT–SM)

Mobile-originated (MO) short messages are transported from the MO–capable handset to the SMSC and can be destined to other mobile subscribers or for subscribers on fixed networks such as paging networks or Internet protocol (IP) networks (including the Internet and private e-mail networks). Mobile-terminated (MT) short messages are transported from the SMSC to the handset and can be submitted to the SMSC by other mobile subscribers via MO–SM or by other sources such as voice-mail systems, paging networks, or operators.

For MT–SM, a report is always returned to the SMSC either confirming the short message delivery to the handset or informing the SMSC of the short message delivery failure and identifying the reason for failure (cause code). Similarly, for MO–SM, a report is always returned to the handset either confirming the short message delivery to the SMSC or informing of delivery failure and identifying the reason.

Depending on the access method and the encoding of the bearer data, the point-to-point short messaging service conveys up to 190 characters to an SME in GSM networks and from 120 to 205 in IS–41 networks.

In GSM networks, the type of messaging service is identified by the protocol identifier information element, which identifies the higher-level protocol or interworking being used. Examples are telex, group 3 telefax, X.400 messaging, European Radio Messaging System (ERMES), and voice telephone.

In IS–41 networks, the service type is distinguished by use of the teleservice identifier. Basic teleservices include the following:

• Cellular messaging teleservice (CMT)
• Cellular paging teleservice (CPT)
• Voice-mail notification teleservice (VMN)

CMT differs from the CPT due to the inclusion of a reply mechanism that enables a user or network acknowledgment to be selected on a per-message basis. The user acknowledgment includes a response code that paves the way for powerful interactive services between SMSCs.

Many service applications can be implemented by combining these service elements. Aside from the obvious notification services, SMS can be used in one-way or interactive services providing wireless access to any type of information anywhere. By leveraging new emerging technologies that combine browsers, servers, and new markup languages designed for mobile terminals, SMS can enable wireless devices to securely access and send information from the Internet or intranets quickly and cost-efficiently. One of these technologies where SMS can provide a cooperative, rather than a competitive, approach is the WAP, which allows transport of data for mobile wireless users.

A generic network infrastructure for realizing the innovative SMS services is depicted in Figure 2.

Figure 2. Network Infrastructure

Some of the potential applications of SMS technology, utilizing both MT–SM and MO–SM where appropriate, include the following:

• Notification Services—Notification services are currently the most widely deployed SMS services. Examples of notification services using SMS include the following:
  • Voice/fax message notification, which indicates that voice or fax mail messages are present in a voice mailbox
  • E-mail notification, which indicates that e-mail messages are present in an e-mail mailbox Reminder/calendar services, which enable reminders for meetings and scheduled appointments.
• E-mail Interworking—Existing e-mail services can be easily integrated with SMS to provide e-mail to short messaging and mobile e-mail and message escalation.
• Paging Interworking—Paging services integrated with SMS allow digital wireless subscribers to be accessible via existing paging interfaces, as well as escalation of messages.
• Information Services—A wide variety of information services can be provided by the SMS, including weather reports, traffic information, entertainment information (e.g., cinema, theater, concerts), financial information (e.g., stock quotes, exchange rates, banking, brokerage services), and directory assistance. SMS can support both push (MT) and pull (MO) approaches to allow not only delivery under specific conditions but also delivery on demand, as a response to a request.
• WAP Integration—SMS can deliver notifications for new WAP messages to wireless subscribers but can also be used as the transport mechanism for WAP messages. These messages can contain diverse information from sources that include databases, the World Wide Web, e-mail servers, etc.

Mobile Data Services
The SMSC can also be used to provide short wireless data. The wireless data may be in interactive services where voice calls are involved.

Some examples of this type of service include fleet dispatch, inventory management, itinerary confirmation, sales order processing, asset tracking, automatic vehicle location, and customer contact management. Other examples may be interactive gaming, instant messaging, mobile chat, query services, mobile banking, etc.

Customer Care and Management
The SMSC can also be used to transfer binary data that can be interpreted by the mobile device without presentation to the customer. This capability allows the operators to administer their customers by providing a mechanism for programming the mobile device. Examples of such services include mobile device programming, which allows customer profiles and subscription characteristics to be downloaded to the mobile device (customers can be activated/deactivated based on the data downloaded) and advice of charge, which enables the SMS to be used to report charges incurred for the phone call (e.g., calls made when roaming).

One interesting method to provide customer support is to offer a list of answers to frequently asked questions via short message. SMS also can be used to distribute general information about other products and services being offered by the service provider, thus guaranteeing maximum penetration of the advertising over the existing customer base. In a different scenario, a service provider may want to deliver short messages to subscribers to remind them of, for example, past-due payments, instead of reminding them over traditional mail or courier delivery, therefore reducing cost and ensuring that the message is delivered to its destination in a timely manner.

5. Mobile-Terminated Short Message Example

Figure 3 depicts the successful MT—SM scenario for GSM.

Figure 3. MT—SM Scenario (GSM)

1. The short message is submitted from the ESME to the SMSC.
2. After completing its internal processing, the SMSC interrogates the HLR and receives the routing information for the mobile subscriber.
3. The SMSC sends the short message to the MSC using the forward short message operation.
4. The MSC retrieves the subscriber information from the VLR. This operation may include an authentication procedure.
5. The MSC transfers the short message to the MS.
6. The MSC returns to the SMSC the outcome of the forwardShortMessage operation.
7. If requested by the ESME, the SMSC returns a status report indicating delivery of the short message.

Figure 4. MT Short Message Scenario (IS—41)

1. The short message is submitted from the ESME to the SMSC.
2. The SMSC sends an acknowledgement to the ESME, indicating reception of the short message.
3. After completing its internal processing, the SMSC interrogates the HLR.
4. The HLR sends the routing information for the mobile subscriber to the SMSC.
5. The SMSC sends the short message to the MSC using the SMSDPP Invoke operation.
6. The MSC transfers the short message to the MS.
7. The MS returns an acknowledgement to the MSC.
8. The MSC returns to the SMSC the outcome of the SMSDPP operation.
9. If requested by the ESME, the SMSC returns a delivery receipt indicating successful delivery of the short message.

6. Mobile-Originated Short Message Example

Figure 5 depicts the successful MO–SM scenario, utilizing the GSM method. The IS–41 method for the MO-SM scenario is depicted in Figure 6.

Figure 5. MO—SM Scenario (GSM)

1. The MS is powered on and registered with the network.
2. The MS transfers the SM to the MSC.
3. The MSC interrogates the VLR to verify that the message transfer does not violate the supplementary services invoked or the restrictions imposed.
4. The MSC sends the short message to the SMSC using the forwardShortMessage operation.
5. The SMSC delivers the short message to the SME (and optionally receives acknowledgment).
6. The SMSC acknowledges to the MSC the successful outcome of the forwardShortMessage operation.
7. The MSC returns to the MS the outcome of the MO-SM operation.

Figure 6. MO—SM Scenario (IS—41)

1. The MS transfers the SM to the MSC.
2. The MSC interrogates the home SMSC to verify that the message transfer does not violate the supplementary services invoked or the restrictions imposed. The MSC sends the short message to the home SMSC using the SMSPP Invoke operation.
3. The SMSC delivers an acknowledgment to the MSC.
4. The MSC returns order release to the MS.
5. The SMSC queries the HLR for the location of the destination MS.
6. The HLR returns the destination (MSC) serving the destination MS.
7. The SMSC delivers SM to the MSC serving the destination MS.
8. The SMSC delivers the short message to the MS.
9. The MS acknowledges to the MSC the successful outcome of the SMSDPP operation.
10. The MSC returns to the SMSC the outcome of the MO–SM operation (delivery successful).

7. SMS Applications

SMS was initially designed to support limited-size messages, mostly notifications and numeric or alphanumeric pages. While these applications are and will continue to be widely used, there are more recent niches that SMS still can exploit.

Short bursts of data are at the heart of many applications that were restricted to the world of data networks with fixed terminals attached to a local-area network (LAN) or wide-area network (WAN). However, many of these applications are better served if the data communication capabilities could be added to the mobility of the station. Thus, a waiter who can charge a customer's credit card right at the table, at any time, instead of going to a fixed POS terminal located by the register will be able to help customers in a faster, more convenient way.

Also, the ability to track the location of a moving asset such as a truck or its load is very valuable for both providers and clients. This application, again, just needs to interchange small amounts of information, such as the longitude and latitude at a current time of the day, and perhaps other parameters like temperature or humidity.

This application does not necessarily require the monitored entity to be in movement. The requirements are basically short, bursty data and a location that has digital network coverage. For example, in a neighborhood, it would be faster, easier, and cheaper to drive a truck from the local power company, which interrogates intelligent meters to obtain their current readings and then forwards them via short message to a central data processing center to generate the billing. Similarly, delivery trucks could be alerted of the inventory of a customer running low, when the truck is close to the customer’s facilities. The truck driver could place a quick phone call to the customer to offer a short-time replenishment at a low cost for the distributor.

Another family of applications that can use SMS as a data transport mechanism is banking. It is no secret that automated teller machine (ATM) and Internet transactions are less costly than transactions completed at a branch. Internet transactions are even cheaper than ATM transactions. Therefore, enabling wireless subscribers to check their balances, transfer funds between accounts, pay their bills and credit cards is valuable, not only for the subscriber but also for financial institutions.

Entertainment applications are also good drivers of SMS usage. Examples of these are simple short message exchanges between two parties (“texting”) or between multiple participants (“chat”). Also, delivery of information that the subscriber can tailor to his or her lifestyle represents an attractive proposition for wireless users.

Wireless Web browsing allows the users to search for information without the physical restrictions of a PC. College students certainly appreciate not having to go to the computer lab or their dorm to check e-mail or find out what the required book is for the semester that is about to start.

E-mail continues to be by far the most used wireless data application. However, handsets are evolving quickly and are including more and more functionality that supports newer applications at the same time that user friendliness increases. Probably the next big success beyond wireless Web will be Internet shopping and other e-commerce applications such as electronic coupons, advertising, etc.

The potential for applications is enormous, and new needs appear to arise constantly, demanding a solution that may travel over SMS.

Glossary

ATM
asynchronous transfer mode

BS
base station

BSC
base station controller

BTS
base transceiver station

CDMA
code division multiple access

CMT
cellular messaging teleservice

CPT
cellular paging teleservice

ERMES
European Radio Messaging System

ESME
external short message entities

ETSI
European Telecommunications Standards Institute

GSM
Global System for Mobile Communications

HLR
home location register

IN
intelligent network

IP
Internet protocol

LAN
local-area network

MAP
mobile application part

MO
mobile originated

MO–SM
mobile-originated short message

MSC
mobile switching center

MT
mobile terminated

MT–SM
mobile-terminated short message

PDA
personal digital assistant

POS
point of sale

PP
point to point

SIM
subscriber identity module

SM
short message

SMD
short message delivery

SMD–PP
short message delivery–point to point

SME
short messaging entity

SMS
short message service

SMSC
short message service center

SS7
signaling system 7

STP
signal transfer point

TCAP
transactional capabilities application part

TDMA
time division multiple access

VLR
visitor location register

VMN
voice-mail notification

VMS
voice-mail system

WAN
wide-area network

WAP
wireless application protocol