The Brave New World of Wireless Technologies: A Primer for Educators

• By Gerald L. Boerner
• 09/26/02

Have you just received funding to install a network in one of your campus’s older buildings? Great! Now what? Why not opt for wireless? Here, Jerry B'erner offers some basic knowledge of wireless networking.

How do you retrofit an older building with today’s networking infrastructure? If the building is built with thick interior walls, or with bricks, or is otherwise architecturally unique, your options to run network cabling on the surface of walls may be limited. You may also discover that you do not have easily accessed spaces above the ceilings, (e.g., no “false” ceilings) into which to install the cabling. And the installation of either copper wire or fiber cabling may require thousands of feet of cable and many hours of painstaking labor to connect. Are there any alternatives to the installation of physical wiring

Five years ago the answer would have been a resounding no! Today we can safely answer the same question with an emphatic yes. Wireless local area networks (WLANs) are now feasible and available at reasonable prices from a variety of vendors. However, the array of acronyms that face educators is imposing and overwhelming; the technical staff in your networking group may not be fully aware of the options. In most colleges and universities, networking personnel are much more comfortable with wired local area networks (LANs). What is ‘Wi-Fi’ anyway? Do we need to understand the difference between FHSS (Frequency Hopping Spread Spectrum) and DSSS (Direct Sequence Spread Spectrum)? While the technical details of these implementations of wireless communications are beyond the scope of an introductory article, we will examine the technologies available for implementing wireless networks today and suggest guidelines for selecting the most appropriate for our colleges and universities.

The Traditional Wired Network

Starting in the mid-1980s, the choice focused our attention to three aspects of network infrastructure: cost, speed, and reliability–we could pick any two! Therefore, we arrived at the following compromises:

• High speed and low cost: Ethernet at the sacrifice of relia bility
• Low cost and high reliability: AppleTalk at the sacrifice of speed
• High speed and high reliability: Token Ring at the sacrifice of cost

Today, this picture has changed substantially. But while our choices are much different, we are still limited to two of the three elements when designing a wired network. We introduce these concepts here so that as we examine wireless technologies, we can focus on the same three factors–speed, cost and reliability.

The Wireless Network

A wireless LAN requires essentially the same components as a wired LAN: a network interface card (NIC), a communication media (copper cable, fiber optics, etc.), a set of rules that follow a standard (protocol) for interpreting the communication signal, and an operating system that understands and maintains the connection between the local and remote computer. What differentiates a wireless network is the use of non-physical media for carrying our information between nodes of the network. A wireless LAN uses several different bands of the frequency spectrum; these frequencies are outside of the normal visual spectrum.

A wireless LAN adds to this mix a special device, the Access Point (AP) to the network. This device communicates with both the wireless device through the Radio Frequency (RF) signal and the wired network through standard protocols like Ethernet. In addition, both the Access Point and the NIC must include antennas to allow access to the RF spectrum. The key elements in designing a wireless LAN are the number, placement, and configuration of Access Points for optimal performance.

Wireless Networking Standards

Wireless LANs have been implemented in recent years via several standards. However, only the IEEE standards defined by Project 802.11 have resulted in sufficient production of devices that enable us to implement WLANs in our colleges and universities. Two variations of this standard are now producing devices for implementing our WLANs: IEEE 802.11b (11 Mbps in the 2.4 GHz band) and IEEE 802.11a (54 Mbps in the 5 GHz band). Both of these technologies function in the unlicensed spectra: the former uses the ISM band while the latter uses the U-NII band. Which one do we choose? Let’s take a closer look at the strengths and weaknesses of these technologies.

IEEE 802.11b is the more mature of the two technologies, and devices (NICs and Access Points) compliant to this specification began appearing in 2001. These devices are available at a modest price and have an effective throughput that is adequate for most normal WLAN applications in the office, lab, or classroom. This throughput fluctuates as a function of the number of devices sharing the channel, distance, and obstacles through which the signal must pass, but in general ranges between 2 and 11 Mbps. The key to deploying this technology is the placement of the Access Points and the assignment of computers to frequency channels to spread the load.

The downside of the 802.11b standard is the relatively slow speed of transmission. Since the maximum speed set by the standard is 11 Mbps, throughput for these devices is the slowest of the 802.11 family of protocols. In addition, the 2.4 GHz range is relatively limited and has only three communication channels available–these channels must be assigned carefully in areas of dense wireless use, such as computer labs or in smart classrooms. Finally, the major weakness of 802.11b lies in security; the use of the Spread Spectrum (DSSS) technology and Wireless Equivalent Privacy (WEP) offers only very basic protection of the data being exchanged.

IEEE 802.11a is the newer technology on the scene, with devices compliant to this standard only appearing in the marketplace in 2002. This technology has a higher throughput at short ranges (up to 10 feet), making it the candidate for use in bandwidth-intensive applications such as multimedia. Unlike the three channels available to 802.11b, 802.11a has eight separate communication channels. This enables more computers to be connected without taxing the system. The use of a multiplexing technology, OFDM, also provides for enhanced security, although it still employs WEP as its major security component.

Again, on the downside, 802. 11a currently has several severe drawbacks. A major disadvantage lies in the chip production technology required; chips cannot be produced as CMOS chips, but must use more expensive technologies. Until the volume of sales of these chipsets increases, 802.11a devices tend to be much more expensive than 802.11b chipsets. In addition, it is a less mature technology and must work through the refinement process. Finally, 802.11a is reliable within a range of 10 feet, but the speed drops dramatically beyond 20 feet. This requires that Access Points be located more closely to the users to maintain both reliability and speed.

For a better understanding of wireless standards, we need to return to the basic three elements that characterize a network: speed, cost, and reliability. We must remember that we can have only two of these. So where do our wireless technologies stand in this analysis? We have already stated that a designer can choose which two of the three elements we value the most. When this analysis is applied to wireless technologies, what do we get? Let’s take a closer look.

• High speed and low cost: The IEEE 802.11a devices
• Low cost and high reliability: The IEEE 802.11b devices
• High speed and high reliability: At present, no wireless technology meets these criteria; we must stay with our wired LAN technologies like fast, switched Ethernet to meet this requirement!

Enhancements to the 802.11 standards offer solutions in the future, but our present offerings are limited to those specified above. When products start appearing for some of the emerging standards, this scenario needs to be revisited.

While a variety of technologies exist for implementing wireless local area networks, the IEEE Project 802.11 family of standards is the most promising at this time. Which of the 802.11 standards is superior? That question is harder to answer, due to the differences in RF band (ISM vs. U-NII) and access technology deployed (DSSS vs. OFDM). In the long run, 802.11g and/or 802.11i will probably offer the most promising solution. These technologies are still awaiting implementation, however. When faced with the choice of selecting 802.11a or 802.11b, the safest choice will probably be 802.11b except in applications that require higher throughput over a restricted range.

Security Issues

Security is the major drawback of wireless LANs. Basic security can be provided by WEP. This is sufficient to start with, as long as the security features are enabled and the NICs support 128-bit encryption. However, WEP is only basic security and is not sufficient for critical data like student records or other secure transactions.

Additional, sophisticated devices from Cisco Systems and 3Com are required to allow more reliable authentication. These solutions are implemented by using a combination of more advanced Access Points and a RADIUS server that maintains a list of the authorized MAC addresses that are permitted to log into the WLAN.

Current Access Points allow the WLAN to be enabled without requiring that encryption be turned on. In addition, many Access Points allow their Service Set Identifier (SSID) code to be broadcast frequently, so outsiders may be able to gain access to the WLAN. Proper configuration can provide a reasonable level of security, but care must be taken to implement and use security options consistently.

The basic WEP protocol incorporated into most IEEE implementations is inadequate for high-security applications. This problem can be resolved by selecting augmented security schemas and authentication techniques. Future standards are being developed to incorporate these changes into the wireless protocols. However, if high-security applications must be accessed, the wired LAN is still the recommended.

Opting for Wireless

Wireless LANs should be seriously considered when upgrading campus networks. The technology has matured and provides a positive set of advantages, including: cross-vendor interoperability, practical interference-free communication over reasonable distances, and minimal security that can be augmented by several emerging technologies. Access Point devices have advanced to allow scalable connection with the wired campus infrastructure, and students and faculty can roam the campus and maintain their network connection. Above all, retrofitting older buildings with networking using wireless technologies lowers the overall cost of ownership and facilitates faster installation, simplicity, and flexibility; and, except for connecting Access Points, physical wires no longer need to be run through walls or between floors.