2.15. Identifying the Basic Characteristics of Various Internet Technologies

The Internet has become a tool that most business cannot afford to be without. In addition, most U.S. households now have some form of Internet access. The question is no longer whether we will connect to the Internet, but rather how we will connect to it. Many technologies have been developed to give users more bandwidth on their Internet connections and thereby make the Internet an even more useful tool.

2.15.1. Critical Information

There are many technologies from which an individual or an organization can choose to provide access to the Internet. Some technologies are inherently much faster than others, but they all have advantages as well as disadvantages. In this section, we will discuss the characteristics of each of the main Internet access technologies. We will point out the main advantages as well as any disadvantages of each one.

2.15.1.1. Digital Subscriber Line (xDSL)

The term Digital Subscriber Line (xDSL) is used collectively to refer to all of the digital subscriber lines. The two main categories of xDSL are Asymmetric Digital Subscriber Line (ADSL) and Symmetric Digital Subscriber Line (SDSL). Both types use technologies on common tele-phone lines to increase the bandwidth of the line. ADSL can provide data rates from 1.5 to 9Mbps when receiving data (referred to as downstream rate) but only 16 to 640Kbps when sending data (referred to as the upstream rate). ADSL allows the subscriber to use the telephone wires for voice as well as data simultaneously. SDSL can support data rates up to 3Mbps in both directions, but SDSL does not allow the use of telephone wires for both voice and data simultaneously. Both technologies are growing in popularity and are used by small- to medium-sized businesses as well as in homes for fast connections to an ISP and thereby to the Internet.

2.15.1.2. Broadband Cable (Cable Modem)

Many homes are currently wired with cable TV connections. The coaxial wire that cable TV providers use can provide significantly more bandwidth than a standard telephone line. Because of this, many cable TV companies have begun offering broadband Internet access as part of their packages. This requires a special device that converts the signal from the coaxial cable into a signal that the computer can understand (referred to as a cable modem). Broadband cable using cable modems currently offers data rates up to 2Mbps in many areas of the United States. This technology is expected to continue to grow. It is used primarily by individual households as part of a "cable package," but some small- to medium-sized businesses also use this technology for Internet access.

2.15.1.3. Plain Old Telephone Service (POTS)/Public Switched Telephone Network (PSTN)

Whether you use the more technical term Public Switched Telephone Network (PSTN) or the term that was coined by telephone company personnel, Plain Old Telephone Service (POTS), you are referring to the normal telephone lines that are used to provide voice telephone service to millions of people all over the world. The main advantage of these types of lines is that they are available almost everywhere. You can use a PSTN line and a modem to connect to an ISP and gain a connection to the Internet that you can use to connect to servers all over the world. The main disadvantage of these lines is that they are very limited in bandwidth. Most PSTN lines offer a data rate of only about 52Kbps. It is possible to combine multiple modems and multiple lines into the same data stream (referred to as multilink), but this is rarely done nowadays because of the other broadband options. Still, many people use PSTN lines to obtain slow but inexpensive access to the Internet. (Most ISPs offer a PSTN price per month that is much lower than their broadband price per month.)

2.15.1.4. Satellite

A less common form of Internet access is through a satellite dish. Some satellite TV providers have bundled Internet access into their offerings along with TV packages. Typically, this service is only available as a download and the upload must be provided with a telephone line, DSL, or other type of media, but some companies are offering uploads to the satellites. Typically download speeds are between 1 and 2Mbps, but upload speeds are much slower (generally 128Kbps or less).

2.15.1.5. Wireless

It is also possible to connect to the Internet through completely wireless technologies. This is a different concept than wireless technologies that are used within networks to connect to wireless access points. In contrast, wireless Internet access is typically acquired from Personal Digital Assistant (PDA) devices and other mobile devices such as cell phones. CDMA and GPRS are the two main technologies used. Both of these offer data rates of 45 to 70Kbps.

2.15.2. Exam Essentials

Know the characteristics of xDSL. xDSL is a term used to refer to all of the digital subscriber line technologies, including ADSL and SDSL. The biggest difference between ASDL and SDSL is that ADSL has a much slower upstream rate relative to its downstream rate, whereas SDSL is capable of the same data rate in both directions. ADSL can support voice and data simultaneously on one line, whereas SDSL cannot. The data rate of xDSL varies between providers, but the downstream rate can usually exceed 1.5Mbps.

List the characteristics of broadband cable Internet access. Broadband cable Internet access is provided by cable TV companies through the coaxial cable that is located in a user's home. It requires a special piece of equipment called a cable modem, which is typically provided by the cable TV company. Broadband cable access can currently support data rates up to 2Mbps.

Describe the characteristics of the PSTN or POTS network. The PSTN or POTS network refers to the regular telephone lines that are installed throughout the United States as well as the rest of the world. Computers can be connected to these telephone lines with the standard modem included on most computers. The main advantage of using this type of network is the fact that it is available in most locations. The major disadvantage of using PSTN for Internet access is that it's very slow compared with other technologies.

Know the characteristics of satellite Internet access. Satellite Internet access is generally available from satellite TV providers. Downstream data rates with satellite are typically much faster than upstream data rates, and many satellite companies require that you use another media for upstream transmissions. Satellite Internet access downstream rates are currently advertised in the range of 1.5 to 3.0Mbps.

Describe wireless Internet access. Completely wireless Internet access is now available for use with cell phones and PDAs. The current technologies of CDMA and GPRS both offer 45 to 70Kbps speed.