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Wireless Networking Frank Steen Director of Computer Services, Faculty of Arts and Sciences, Harvard University October 5, 2001 Wireless networking is evolving. This paper will give a snapshot of the situation, particularly as it applies to universities, in October 2001. The Changed Campus in the Wireless World We all believe that wireless networking will change our campuses. Today, there are already several campuses with fully developed wireless infrastructures and many more campuses with significant and growing wireless networks. An informal survey of computing leaders at a number of such campuses1 shows that wireless on campus leads to some obvious results. Students, faculty and staff move to own more laptops and take them from place to place on campus more than the ever did with wired connections. Dining rooms, libraries, lawns, athletics facilities, offices, hallways and classrooms become places for email, surfing the net, looking at course web pages and instant messaging. For students with wireless laptop computers, there is no longer a need to go to computer labs--no need to use library terminals. The wireless step is the critical one that frees students from the confines of fixed locations. Faculty too, takes their computers between offices, labs, libraries, classrooms and meetings and the resources of the net are available to them. In the classroom it is much easier to have students see assignments, exercises, and research on the wireless net and it is easier from them to play as well. As a result every classroom can be a computer lab or a major distraction. Wireless networking does not mean that every member of the university community will be carrying a device with them wherever they go. These devices are heavy and not always a welcome burden. There is still a stigma attached to the student who types in notes in class, with or without a network connection—it does make noise and bother others. Wireless devices are expensive and those that have them rightfully fear theft and breakage. Students carry laptops in backpacks and they are tossed, stepped on and otherwise mistreated and loss of the use of a laptop computer can render a student nearly helpless in a computerized world. In class students on the wireless net can be physically present but involved with unrelated distracting net activities. This bothers many instructors who have placed overt restrictions on the use of computers during class. Despite wireless on campus there is still a future for campus computer labs. The labs themselves can become a place for better interaction as some students with wireless computers sit with and compare notes with those on lab systems. Students who do not 1
Obtained at meetings where wireless networking was discussed including Harvard, Penn State, Carnegie Mellon, University of Colorado, UCLA, Wisconsin, Michigan, and Dartmouth.
have their wireless devices with them can use computers in the labs as before. With the combination of fixed computers and wireless the lab becomes more of a collaboration center, which is many cases is a desirable result. Of course, collaboration of this intensity can also lead to problems, which are a new challenge to instructors. An interesting side effect of a wireless campus is printing. Users of wireless devices will expect to print wherever they are and many printing systems do not support this option. Campuses that charge for printing or have multiple printing systems, different in the library and in computer labs for example, will be motivated to find a solution to let any wireless user print to whatever public printer is convenient. Hopefully software solutions, not presently available for all uses, will be developed to enable such ubiquitous printing, even with charging for use. In meetings, too, wireless computers change the way the participants behave. During a presentation or discussion wireless participants can go to websites and check what the speaker is saying. This indeed happens frequently at meetings of the University Common Solutions Group, where wireless networked communications have been available for several years. It is a new experience for a presenter to stand before a group, in which everyone is reading or typing on their computer. The participants also use messaging to comment on the topic at hand, to take polls and to plan for future presentations. Everyone does not accept this behavior! In this paper I list not only the primary wireless standard being installed by universities, 802.11b, but also the commercial wireless offerings on digital phone nets and special networks. Students, faculty and staff may wish to use these external wireless options until wireless nets are installed everywhere on campus or in lieu of campus networks. Indeed, in law schools, business schools and other professional schools many students use these external wireless nets because of their presence in the professional world. The external wireless nets remove nearly all control of wireless from universities. For example, when the Harvard Business School turned off wireless access on their 802.11b net during final exams, they found that students still tried to connect via external commercial wireless. Despite their disadvantages—slow speed and cost—the commercial providers will likely continue to play a role in the wireless plans of members of the university community.
Wired verses Wireless Now that most universities have their wired network infrastructure built there is suddenly a demand for a new wireless infrastructure. Does this mean that the wired network in obsolete? Of course not! The whole network infrastructure contains a place for wired and wireless connections. Every wireless access point using the 802.11 standards needs a wired connection. Wiring for wireless access points requires a different topology than for traditional wired jacks, so a network mixing both wireless and wired connections may need as much or more wire than before—even with fewer jacks. If the 3G or 4G digital standards (see below for the explanations of standards and terminology) come into place,
which at the moment looks less than certain, and no wired access points are needed on campus, a wired network still has its advantages. One advantage is dedicated bandwidth. Wired connections today are generally switched, which means that each user has access to the full available bandwidth. This means that a user of a 10 megabit connection has the full 10 megabit bandwidth at his disposal. The full bandwidth is often necessary for quality multimedia presentations. Wireless solutions use hub-based technology—the bandwidth is shared. So a hundred wireless users on an 11 megabit connection at an access point will share the 11 megabits. This means slow access if everyone is accessing the net at once; the result is not adequate for multimedia. It appears that networked multimedia will rely on wired networks for some time. Another advantage of wired over wireless is access control and security. Wired connections have the advantage of physical access control. If a person cannot physically get to the network jack, he cannot use the wired network. Wired security methods are standard and proven—it is possible to reach a high level of protection for data and communications. This is important for university networks with secure information such as student records and financial data. Wireless security standards have not been settled and there are many ways that wireless networks can be compromised. Even with the use of VPN and other security methods that can be adapted to wireless today, access may be so difficult that network administrators will be reluctant to put them into place. Most existing wireless networks today lack the most fundamental security So, while wireless has big advantages for users, it will not spell the doom of wired connections The Details There are many confusing references to “wireless” in the media, and I will attempt to clarify some of the options, protocols, and possibilities in this paper. Among technologies referred to as wireless are cellular telephones phones, packet radio, remote controls, ham radios, and wireless Ethernet. This paper will deal with those wireless computer network methods most likely to be present at a university. Today’s Standard: IEEE 802.11b The high speed wireless network world in education today is concentrated around the IEEE 802.11 protocol. The most used version today is 802.11b, which works in the 2.4GHz2 unlicensed microwave band, and is capable of theoretical speeds of up to 11 megabits per second (mbps)3. High-end access points, with a radio transmitter/receiver and antenna, have a range of about 300 feet; home access points cover about half that 2
GHz: GigaHertz, a frequency measure meaning a billion vibrations per second. The frequency refers to the band where the service resides. Wireless service generally resides on unregulated microwave frequencies like 2.4 GHz. 3 Mbps: megabits per second or one million bits of data per second. Kbps is kilobits per second or thousand bits per second. Kpbs is also referred to as kbaud or kilobaud.
distance. Wireless cards from vendors such as Oronoco and Cisco contain a radio and antenna able to communicate using “half-duplex” communications, which means that they either listen or talk but do not do both at the same time. While theoretical top speed of 802.11b is 11 mbs, the practical speed is somewhat less. If the signal is weak—depending on the distance and barriers between receiver and transmitter, the speed is considerably less—as slow as 1 mbs. Actual effective speed is dependent not only on the signal strength but on factors such as number of concurrent users, interference and antenna effectiveness. Since the wireless access points provide shared network connections the bandwidth is split among users, so the more users the slower the access—an important factor in dense university environments. The antenna placement is important and newer laptop computers have built in antennae, which- may help to increase effective speed. Other hindrances are physical obstructions, such as book storage and mortar walls, that are common at Universities and can slow performance even more. Even in the best of conditions testers have found themselves limited to about 8 mbs, and users should not expect even that under most conditions. Security is an issue 802.11b wireless networking. The Wired Equivalent Privacy encryption (WEP) has many limitations and is not finding much practical use. Users of 802.11b are using what can be termed as temporary security solutions such as VPN (virtual private networks), while new security protocols are being developed. Unfortunately at present there is no generally accepted solution. Practically speaking 802.11b still looks like an excellent choice for university users browsing the Web, using email and such, but speed considerations make it less than ideal for video-based online multimedia. As networked multimedia gains in importance it is expected that universities will look to faster protocols. Of course, universities are concerned about the security issues and until a broadly accepted solution is worked out, security may keep some universities from implementing 802.11b. Universities will have to weigh these considerations as they decide whether or not to implement an 802.11b wireless solution. Universities do face the reality that more and more students are moving to 802.11b capable laptop computers and even personal digital assistants (PDAs). The newest models come with pre-installed antennae and easy-to-install or pre-installed wireless cards, which make them easy to connect. Also, as 802.11b wireless moves into public places, homes and offices4, more students will arrive on campus equipped, experienced and ready to be wireless. These facts will doubtless increase demand for the installation of a campus-wide 802.11b wireless network. The recommended course for most Universities today at a minimum is to set up experimental wireless areas using 802.11b.
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Starbucks has announced 802.11b connectivity in their coffee shops. There are also neighborhoods where home and business owners have gotten together and put up a free communal 802.11b service. These are known as Freenets and are growing. Airports, Libraries, Schools and other public places are putting in 802.11b reinforcing it as the de-facto wireless standard.
Coming: 802.11a On the horizon is the 802.11a standard. This wireless protocol operates in the less congested 5 GHz range and has a maximum speed of 54 mbit. The transmission range for the wireless radio equipped access points is considerably less than for 802.11b— averaging approximately 60 feet. This will make 802.11a more expensive than 802.11b because of the need for more access points, although manufacturers are working on higher power equipment to increase the transmission range. The shorter range of 802.11a will also require different access point placement than with 802.11b; an upgrade from 802.11b to 802.11a will require rewiring. In addition to the transmission distance issues the new 802.11a is not backwards compatible with 802.11b. Therefore universities that install the 802.11b equipment today and students and faculty that install 802.11b cards in computers will have to make a considerable investment to change to 802.11a. Manufacturers are now gearing up to produce 802.11a chips and equipment, and initially it is expected to be more expensive than 802.11b. The higher speed does make 802.11a better suited for multimedia and universities will have to weigh that advantage against the increased cost. Time will tell whether the 802.11a standard becomes widespread. Other 802.11 protocols: Early wireless using 802.11, 2.4 GHz spectrum used a method known as frequency hopping5 and had transmissions speeds limited to 1.5 to 2 mbit. There remain two types of networks using the slower speed frequency hoping systems: HomeRF and OpenAir. While some manufacturers continue to provide compatibility for these standards in their access points and some non-computer uses of HomeRF6 have emerged, most do not. 802.11b devices, which use spread spectrum7 instead of frequency hopping, are capable of faster speeds and more reliable connections. As a result remaining HomeRF and OpenAir wireless networks are being replaced by 802.11b, with no backwards compatibility. HomeRF is gaining a rebirth in specialty applications such as wireless stereo and automotive safety systems. There are also proposed standards for 802.11e and 802.11g. 802.11e is primarily for voice security and privacy while 802.11g is a proposed way to increase the speed of 802.11b. The equipment for 802.11g would be backwards compatible to 802.11b using the 2.4 GHz frequency, which is a big plus. On the minus side the 2.4 Ghz frequencies are much more congested in the United States and Europe than the 5 Ghz ones used for 802.11a. 802.11g would reach a theoretical transmission speed of 20 Mbps plus and is thought of as a way to get multimedia speeds without having to go to 802.11a. Again, time will tell if this proposed standard is established and can take hold. 5
“Frequency hopping works very much like its name implies. It takes the data signal and modulates it with a carrier signal that hops from frequency to frequency as a function of time over a wide band of frequencies.” (Jim Geier: “Spread Spectrum: Frequency Hopping vs. Direct Sequence”, May 1999 on http://www.wireless-nets.com/whitepaper_spread.htm) 6 wireless MP3, audio books, traffic reports in cars are new uses. See: http://www.homerf.org. 7 “Direct sequence spread spectrum combines a data signal at the sending station with a higher data rate bit sequence…” (ibid)
