A Teacher's Guide to Distance Learning
The options for connectivity between the teaching site and the students are increasing continuously. Students can listen to podcasts while they ride their bikes or walk around the mall; cellphones provide access to the web, graphics and video; wireless networks are available at schools and stores; and Internet access in homes is available through television cables and fiber optics.
Even with increased options for connectivity, the transmission speed is still an issue. The problem is that digital files (especially audio and video) are huge, and they require channels or cables with tremendous capacity to transmit quickly and effectively. The transmission capacity of a cable or a technology is referred to as the bandwidth. The greater the bandwidth, the greater the amount of digital information that can be transmitted per second. There are several options available that teachers and students can use to access the Internet, including telephone, DSL, cable, fiber, satellite, and wireless delivery (see Figure 2). Note that although the table lists the maximum download speeds, these speeds will seldom be realized, due to hardware limitations, latency, simultaneous users, and many other reasons. In addition, the upload speeds are often considerably less than the download speeds.
Technology Maximum Download Speed Analog Telephone Modem 56 Kbps Satellite 1.5 Mbps DSL (Telephone company) 10 Mbps Cable Modem (TV company) 30 Mbps< Fiber (Telephone company) 50 Mbps WiFi (Wireless network) 54 Mbps
Figure 2. Comparison of sample transfer rates.
Standard Telephone Modems
The standard speed for telephone modems is currently 56 Kbps. This speed can provide effective communications via e-mail and websites that do not contain extensive graphics. Advantages of standard modems include low cost (many computers have built-in modems) and the modems' compatibility with standard telephone lines. However, access to the Internet through a standard telephone modem that transmits at 56 Kbps (or less) can be excruciatingly slow -- causing jerky movies, disjointed sounds, and long wait times for downloads.
DSL ModemsDSL stands for Digital Subscriber Line. DSL modems can transmit data to users at up to 9 Mbps. The return rate (back to the ISP or Internet) may not be quite as fast -- only 640 Kbps or so. In most cases, the difference in the transfer rates is acceptable for Internet access because we are most likely to receive large files from the Internet (such as graphics and video) that require the faster rates. On the other hand, we generally do not send back as much data to the Internet (perhaps an e-mail message or a click on a hyperlink). Therefore, the slower rate on the return segment is not detrimental.
A major advantage of DSL technology is that it uses standard, copper telephone lines, and it is available in most areas. A DSL modem (generally supplied by the telephone company) is required, as well as an Ethernet card for your computer.
Fiber Optic ModemsTelephone companies have also installed fiber optic cables into some neighborhoods. Transmitting via fiber can be extremely fast (up to 50 Mbps). Because of the massive bandwidth that is available, the telephone company can then deliver both television and Internet (as well as regular telephone) through the same cable. For example, Verizon offers FiOS (Fiber Optic Service) to homes and businesses in many areas. Installation is required, but is usually included when you subscribe to the service. Other telephone companies offer similar services via fiber.
In most areas, cable companies are offering Internet access through the same cable that delivers television signals to our homes (see Figure 3). If your area has been configured for this service, you can connect a cable line to a network card on your computer (via a cable modem). The main advantage of cable modems is the bandwidth. Cable modems can bring data to your computer between 10 and 30 Mbps. If you have a 10 Mbps network card in a computer, you may be able to receive information up to that speed. A disadvantage of cable modems is that the transfer rate may be slowed if too many people in your neighborhood all connect to the Internet at the same time.
Figure 3. Cable modem in a home.
Satellite DeliveryIt is also possible to receive information from the Internet via satellite. Satellite access is relatively fast, does not require the installation of telephone or data lines, and is not adversely affected by the number of simultaneous users.
Satellite delivery, however, is usually one-way; you cannot send information back up to the satellite (not on a school budget, anyway). In most cases, a telephone line is used to send information back to the Internet or service provider, and the satellite is used to receive information (see Figure 4). This configuration works well in most cases, because the information you send back is generally very small (a mouse click or an e-mail message); whereas, the information you receive can be quite large (video files, Web pages, etc.).
Figure 4. Connecting to the Internet via satellite.
Wi-Fi is a wireless network that can provide access to the Internet. You can set up a wireless network within your home or school by connecting a wireless router to a DSL, cable or other connection. Computers throughout the house or school (that have a wireless receiver) can then connect to the Internet without direct wiring. Depending on the type of wireless equipment you are using, the bandwidth can be extremely fast. However, this will be limited by your connection speed. In other words if you are connecting to the Internet via a DSL modem and then setting up a wireless network, your access to the Internet will be limited by the DSL transfer rates. If you set up a wireless network, you should always be sure to include security (via a password). Otherwise, any one with a laptop or wireless device may be able to connect to your network.
More and more schools and business are offering Wi-Fi hotspots -- places where you can find Wi-Fi connectivity. Some of the hotspots (such as those at airports and cafes) may be free and open to all; others may require a password, subscription or credit card to connect.
Mobile Devices (Cellphones, PDAs, etc.)An increasingly popular method of accessing distance learning materials is via mobile devices, such as cellphones and "personal digital assistants" (PDAs) such as Blackberries. Cellphones communicate with nearby transmitters (on cell towers), which change as the phone moves from location to location. Communicating via cellphones is by far the most mobile technology, although the speed with which data (such as websites) is transferred is not nearly as fast.
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College of Education, University of South Florida © 1999, 2009.