Wireless Networking Handbook
(Publisher: Macmillan Computer Publishing)
Author(s): Jim Geier
ISBN: 156205631x
Publication Date: 09/01/96

During the late eighties, the decreasing size of computers from desktop machines to laptops allowed employees to take their computers with them around the office and on business trips. Computer companies then scrambled to develop products that would support wireless connectivity methods. In 1990, NCR began shipping WaveLAN, one of the first wireless LAN adapters for PCs. Motorola was also one of the initial wireless LAN vendors with a product called Altair. These early wireless network adapters had limited network drivers, but soon worked with almost any network operating system. Rapidly, companies such as Proxim, Xircom, Windata, and others began shipping their products as well. These initial companies were pioneers in the wireless networking arena. They felt their wireless products would feed a market desperately wanting to meet mobility needs. Network managers and system administrators, however, did not trust the technology enough to purchase the pricy wireless adapters. The WaveLAN network adapters, for example, initially listed for $1,400 each. Vendors quickly found that they had to reduce prices. Businesses were afraid these new wireless products lacked security, were too slow (at least slower than ethernet), and were not standardized. Over time, though, vendors began incorporating encryption to protect data transmissions, and operation at higher frequencies increased the bandwidth to near-ethernet speeds. The market also saw a substantial drop in price to $300–$500 per card. The lack of standards, however, limited widespread use of wireless LAN products.

The current depressed state of the wireless LAN market should change as standards mature. The Institute for Electrical and Electronic Engineers (IEEE) 802 Working Group, responsible for the development of LAN standards such as ethernet and token ring, initiated the 802.11 Working Group to develop a standard for wireless LANs. This group began operations in the late eighties under the chairmanship of Vic Hayes, an engineer from NCR. At the present time, 802.11 is still working on the standard. A final standard should pass in 1997.

End users and network managers have had a difficult time showing a positive business case for purchasing wireless LAN components in the office unless there is a requirement for mobility. Most sales of wireless LAN adapters to date have been in healthcare and financial environments. Sensing a bleak market for wireless LAN products, wireless LAN vendors began equipping their wireless LAN components in 1995 with directional antennas to facilitate point-to-point connections between buildings located within the same metropolitan area. These wireless MAN products satisfy a widespread need—the capability to connect facilities where traditional cable installation and leased circuits are costly. The sales of these wireless MAN products have been favorable.

The most widely accepted wireless network connection, though, has been wireless WAN services, which began surfacing in the early nineties. Companies such as ARDIS and RAM Mobile Data were first in selling wireless connections between portable computers, corporate networks, and the Internet. This service enables employees to access e-mail and other information services from their personal appliance without using the telephone system when meeting with customers, traveling in the car, or staying in a hotel room.

Narrowband Personal Communications Services (PCS), a spectrum allocation located at 1.9 GHz, is a new wireless communications technology offering wireless access to the World Wide Web, e-mail, voice mail, and cellular phone service. Vice President Al Gore kicked off the FCC PCS auction in 1995 by selling 30-MHz licenses to television and telephone companies. The total take for 1995 was $7.7 billion. The U.S. government expects to raise $15 billion from the auctioning during 1996.

Because of PCS, the wireless industry is quickly gaining momentum. As a result, a vast number of wireless networking products should appear on the market in 1997. SkyTel began shipping the first PCS product in 1996, a pocket-sized two-way pager, which can receive pages as well as respond.

Wireless Network Architecture

In general, networks perform many functions to transfer information from source to destination.

1.  The medium provides a bit pipe (path for data to flow) for the transmission of data.

2.  Medium access techniques facilitate the sharing of a common medium.

3.  Synchronization and error control mechanisms ensure that each link transfers the data intact.

4.  Routing mechanisms move the data from the originating source to the intended destination.

A good way to depict these functions is to specify the network’s architecture. This architecture describes the protocols, major hardware, and software elements that constitute the network. A network architecture, whether wireless or wired, may be viewed in two ways, logically and physically.

Logical Architecture of a Wireless Network

A logical architecture defines the network’s protocols—rules by which two entities communicate. People observe protocols every day. Individuals participating in a business meeting, for example, interchange their ideas and concerns while they avoid talking at the same time. They also rephrase a message if no one understands it. Doing so ensures a well-managed and effective means of communication. Likewise, PCs, servers, routers, and other active devices must conform to very strict rules to facilitate the proper coordination and transfer of information.

One popular standard logical architecture is the 7-layer Open System Interconnection (OSI) Reference Model, developed by the International Standards Organization (ISO). OSI specifies a complete set of network functions, grouped into layers. Figure 1.2 illustrates the OSI Reference Model.

Figure 1.2  The Open System Interconnection Reference Model.