While there are many factors that can make it difficult to deploy great Internet applications, a key barrier to fulfilling the Internet's promise is the low bandwidth available over the "last mile" -- the connection into peoples' homes. Even if all the funding and development problems associated with building large Web-based applications were solved, the current limitations on the bandwidth over that last mile would prevent users from taking full advantage.
Bandwidth is the "transmission capacity of a computer channel [or] communications line" (The Computer Encyclopedia by Alan Freedman). In analog communication, such as standard telephone lines, bandwidth is expressed in the number of cycles per second, or Hertz (Hz). In the digital world, bandwidth is expressed as the number of bits or bytes per second a line can transmit. This is usually expressed as thousands of bits per second (Kbps) or millions of bits per second (Mbps). A "bit" is the smallest piece of digital data that can be sent, representing a 1 or 0; a "byte" is a group of bits -- usually eight -- capable of storing a single character.
Although most agencies and businesses have internal networks with comparatively good bandwidth -- usually in the 10-megabit range -- they may still suffer from bandwidth deprivation. Current trends promise this problem will only increase in coming years with the proliferation of graphics-based applications that can gobble up bandwidth and as interagency communication increases. Agencies will also need far more bandwidth to take advantage of newly emerging cost-saving technologies, such as computer telephony.
The bandwidth problems agencies face are multiplied many times when it comes to home connections. Until recently, the only low-cost option for Internet home connectivity has been through existing analog phone lines. Many people have cable lines into their homes, but cable networks were optimized to carry video, not digital information. More importantly, most cable systems were built to carry information one way -- from the cable operator to the individual home.
Although about 96 million of the 100 million homes in the country have phone lines, twisted-pair copper telephone wires were designed to serve a technology that's more than 100 years old. Even though the quality of phone service has improved dramatically, and much of the telephone system backend is digital and computer-controlled, the system is still limited to a relatively small carrying capacity. Modern modems rather miraculously push the limits of how much information can be packed into analog telephone's bandwidth and so aren't likely to dramatically improve over the 56Kbps currently available.
It is important to realize that the race to achieve ubiquitous high bandwidth signifies a broader, more important trend than just being able to download Internet graphics faster.
"In each civilization, the ones with the most advanced ability to communicate are the most productive," commented Gregg Giordano of Voice Data Communication Information Technology (VDCIT) of Virginia. "Voice networks aren't designed to move data -- they are too slow; their switching isn't quick enough, and bandwidth isn't great."
What's more, the increase of available bandwidth promises to radically change the ways in which we give and receive information. Currently, phone communication travels through one network, data travels through another and video travels through several (broadcast, satellite and cable). High bandwidth availability promises to combine these various networks so that every transmission -- phone, data and television -- will travel over one network. According to Giordano, the two most important advantages of a single network are that it is easier to administer one network rather than three, and bundling services can lead to lower prices.
With these advantages, many companies are working to provide high bandwidth to the home. Two approaches offer the greatest promise and are becoming available in an increasing number of areas.
Cable: More Than TV
Although the idea of using cable networks to provide Internet access has been debated for some time, only recently have more cable companies actually started to offer it. Unfortunately, many cable companies need to carry out major infrastructure improvements to provide Internet access. The most obvious barrier is that most cable systems were originally designed to carry data one way -- from the cable company to the home. Some companies have worked around this problem by using their cable for the downstream (to the home) flow of data and installing a separate phone line for the upstream flow. For most home uses, such as viewing Web sites or downloading software, the downstream flow is most important. Nonetheless, the two-line solution is more complicated than having a single line.
Some cable companies, such as Jones InterCable in Alexandria, Va., have already invested in the infrastructure to provide two-way cable-modem access at affordable rates. As part of the city's recent 15-year renewal of its cable contract with Jones, the cable company was required to rebuild its local system with more than 200 miles of fiber-optic cable. The new cable will increase the quality and variety of cable TV service and also dramatically improve Internet access for the city as a whole.
Once a cable system has been upgraded for Internet access, it generally provides bandwidth in the 10Mbps range. However, this is shared bandwidth -- more than one household is connected to the same line -- so as the number of subscribers increases, performance tends to decrease. Nonetheless, cable-modem subscri-bers can often expect to get service in the 1.5Mbps range -- about 50 times faster than a 28.8 dial-up modem.
Digital Subscriber Line Technology
Digital Subscriber Line (DSL) technology has been with us for years, but in recent months it, or one of its offspring, has almost continuously been in the news. Put simply, DSL allows far more data to travel on regular twisted-pair phone lines than is possible using the traditional phone network. Generically, DSL technologies are often referred to as "xDSL" technologies. Some of the common flavors of xDSL are described below. Interestingly, some types of xDSL technology can send and receive data at the same time the phone is used for regular phone calls or for sending faxes.
xDSL accomplishes its magic using frequencies far above regular phone traffic. Standard phone lines use no more than about 4KHz of bandwidth. This is not a limitation of the copper wire, but of filtering devices within the phone network itself. Copper is perfectly able to carry higher-frequency signals -- which can carry more data -- so xDSL sends signals in these upper frequency bands. For those types of DSL that use frequencies well above those used by analog phone, the xDSL and phone traffic do not clash. The two signals are separated at the user's end with a splitter that routes the phone traffic to the phone and the xDSL transmissions to the xDSL-enabled device. The phone company also needs to install specialized xDSL equipment, but this is far less expensive than having to install new cable to each home.
Although copper does carry higher frequencies, it imposes some distance limitations on how far it will carry them. The higher the frequency, the shorter the distance. It is this limitation that has given rise to the varieties of xDSL technology.
The original DSL technology is now used to transmit ISDN (Integrated Services Digital Network) signals, but because this flavor uses frequencies that overlap traditional telephones, the same line cannot be used for regular analog phone and digital traffic. Nonetheless, DSL does have greater data-carrying capacity -- 160Kbps for up to 18,000 feet from the telephone distribution center -- and, if the user switches to digital phone, voice and data can be transmitted and received over the same line.
HDSL (High Data Rate Digital Subscriber Line) transmits in higher frequencies than DSL and achieves transmission rates from 1.5Mbps to a bit over 2Mbps. However, it requires two lines for 1.5Mbps speeds and three lines for 2Mbps. It will, therefore, not likely be widely adopted in home or small business connections.
SDSL (Single Line Digital Subscriber Line) achieves transmission in the 1.5Mbps range using a single line. However, it has a reach of only 10,000 feet from the phone office, and ADSL (see below) provides downstream rates of more than 6Mbps over that distance.
ADSL (Asymmetric Digital Subscriber Line) is the variant of DSL consistently in the news in the last few months. The "asymmetric" in the name refers to the difference between its downstream and upstream rates. At the low end of ADSL service, the downstream rate is 1.5 Mbps, with an upstream rate of 16-64 Kbps. It can deliver these rates up to 18,000 feet from the phone distribution center. Within 12,000 feet, it delivers up to 6Mbps downstream.
The differential between downstream and upstream speed is what "buys" the extra distance -- signals sent asymmetrically interfere with each other far less than symmetric signals, thereby minimizing signal deterioration. Fortunately, this lopsided speed fits most home applications in which users primarily download data -- whether text, graphics or software -- or are accessing city or state services. In all of these cases, the bandwidth of the upstream data flow is far less important than the downstream flow.
ADSL operates in frequencies well above regular phone service, so it does not interfere with the phones, which means no new lines need to be strung into the home. Perhaps more importantly, ADSL lines are not shared. Each household has a unique connection between it and the phone company, making ADSL lines inherently more secure than cable's shared-bandwidth scheme.
VADSL (Very High Data Rate Digital Subscriber Line) started out as ADSL with a shorter distance limitation. In fact, within 1,000 feet of the phone distribution center, it offers speeds faster than 51Mbps. Today, it is more commonly called VDSL because it is expected to eventually deliver symmetrical service. Although VDSL may provide a way for agencies to make very high-speed connections to the Internet, it is unlikely to reach into the average home any time soon. However, in the immediate future, its speed will not be needed in the home where 1.5Mbps to 6Mbps is adequate for most applications.
Finding a Niche
Although cable and ADSL are in many ways competing for the same market -- high-bandwidth access to the home -- and because of the growing demand for high bandwidth, it is likely that both will find a niche. Both have advantages, and to the average user, the details of getting bandwidth are less important than just gettingit.
Cable and telephone line ADSL are not the only options for high bandwidth into the home, but they appear to be getting to market first. For example, a growing number of the Baby Bells are beginning to offer ADSL and have announced plans for major rollouts. Nonetheless, other options are certainly on the drawing board, such as the millions being invested in satellite systems that promise to provide high-speed wireless access. For that matter, DSL technology is limited to phone lines. According to VDCIT's Giordano, some efforts have been directed at providing DSL access through the electric power lines into homes -- again pumping data into the home with frequencies separate from those used by the power companies to provide electricity.
Whichever technology makes it into the home over the next few years, it is quite certain that ubiquitous high bandwidth is coming, so it is important for state and local planners to begin working today on the applications that people will be using in the coming years. When high bandwidth does become widely available, whole new vistas of applications become possible. Combining telephone, data and video into one data stream offers incredible possibilities for interactive government and for delivering government services right into living rooms, fulfilling a broad range of user needs. State and local IT departments are well advised, then, to begin planning now how they will make data available as fast as users will be able to receive it.
David Aden is a senior consultant for webworld studios, a Northern Virginia-based Web application development consulting company.
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