Acronym for wireless local-area network. Also referred to as LAWN. A type of local-area network that uses high-frequency radio waves rather than wires to communicate between nodes

Introduction
Wireless communications represent a large market segment in both the analog and digital communications services industry. This article is focused on wireless digital services used to connect computer networks to the internet and to each other. This paper is intended to be a non-technical overview of the technology and its application suitable for general audiences, potential users of wireless services, and investors who may be interested in the business opportunities that are possible.

In this paper we will look at the key enabling technology of wireless internet service, the applicable standards that govern the deployment of wireless networks, and our particular experience with using wireless internet service. One aspect of wireless LANs that is important to emphasize is that the technology is considerably more robust than traditional local area networks (LANs). Wireless networks are quickly becoming popular as wide area networks (WANs) and metropolitan area networks (MANs). Here, we will use the term "LAN" in a generic way but the implication is that all network types and architectures can be included in our discussion.

Wireless technology has significantly improved our ability to deliver internet services reliably and at low cost. Lets look at some technology issues first and then review our experience with wireless LANs.

Technology Overview
Wireless technology is quite complex and rapidly advancing. While it is not within the scope of this paper to describe details of wireless LANs, I do wish to present some features of the technology. Here is a particularly good resource for information on the subject: The Wireless LAN Alliance (http://www.wlana.com/) . There is also another link to technical summaries provided by Breezecom, Inc. (http://www.breezecom.com/) who have done an excellent job of providing an overview of wireless LAN technology.

Basic Wireless Systems
Wireless communications is a term used to describe a number of technologies ranging from mobile phones to spacecraft telemetry. In fact the term "wireless" goes back to the early days of radio when Marconi developed the concept of wireless telegraphy. Basically we use wireless to mean communication by electrical signals without wire or cable between a receiver and a transmitter.

Here, we are limiting the discussion to a class of wireless communication to move digital signals between computer networks. Figure below depicts the major categories of wireless networks in use today:

This article will be limited to the 2.4Ghz variety of wireless LANs that use the Industrial, Scientific, and Medical (ISM) made available for unlicensed use in the USA and commonly available in the rest of the World. The current technology in spread spectrum communications can be divided into two general classes: frequency hopping (FH) and direct sequence systems (DSS). Both techniques are widely used and use the same frequency spectrum but in very different ways

Network Topologies
Wireless LANs can be deployed in a number of basic topologies. The simplest arrangement is to connect two networks together with a single channel radio using either frequency hopping or direct sequence protocols. Numerous vendors have products for this purpose. The installation that we document here is one of these kinds of topologies as an example. An access point in Melbourne, Florida provides 100Mbs aggregate capacity within a 10 mile radius of any access point location. A Breezecom radio is installed on the rooftop and pointed to the access point location. At the distribution point, proprietary software is used to allocate bandwidth to multiple channel radios and directional antennas. The link is set to be a 256Kbs link with burst capacity to T1 speed. The distribution point uses fiber optic connections to the internet to provide the service. A fixed IP is used and registered a domain name using the IP furnished by an ISP. At the other end we terminate the connection to an NT class PC and then use a proxy service to share the link with a small network. We can allow any user on our backbone network to access the wireless LAN by sharing the proxy service address and protocols.

Other topologies include virtual private networks, wireless footprints within a building or facility, roaming service within wireless "cells", wide area network (WAN), and metropolitan area network (MAN) deployment.

The IEEE 802.11 Standard
The development of any new technology is part theory and part practice. A key issue in telecommunications is the adoption of technical standards that govern the interoperability of equipment to provide a stable environment for deployment of products and services. This does not mean that all vendor equipment will work in the exact same way. A standard sets a norm or performance expectation on the function of the technology -- not its implementation.

The standard that governs the wireless LAN industry is the IEEE 802.11 family of standards that are part of the group that governs ethernet data communications. This standard is evolving and adapting to meet the needs of industry as new technology is developed to allow new product design. An excellent overview of this standard and the committee that is working on it is available at WLANA and can be accessed by via the web. The IEEE working group web page for IEEE 802.11 is also accessible via the web.

Security
Network security is a vital concern in most business applications. The use of wireless LANs introduces some concerns since the net traffic is in a public space. However, the security systems afforded by wireless LANs are formidable and provide levels of security that in many ways exceed the use of wire or fiber optic cable. WLANA provides a Wireless LAN Security White Paper that answers many general questions on security issues.

The use of spread spectrum frequency hopping provides a relatively secure channel by itself. The sender and receiver must be synchronized to the same hop sequence in order to communicate at all. Airwire.net supports five levels of security as follows:

Frequency Hopping Spread Spectrum: this approach is the technology just described. Data packets are spread over short bursts of signal at different frequencies within the wireless bandwidth. This avoids interference and requires the receiver to be synchronized with the transmitter.

Network Identifier Sequence :
Each private wireless network is setup with a unique Network Identifier sequence. ALL stations within that network must be programmed with the correct sequence before they will associate with one of the access points. This sequence would be extremely difficult for an intruder to crack because of the number of possible combinations, which are well above the quintillions.

Data Encryption:
This encryption uses a key that can vary in size from 40 bits to 128 bits. Each bit added to the key doubles the number of combinations an intruder would have to try. The government standard key size is 56 bits which is 7,200,000,000,000,000,000 combinations. Adding several bits increases this number to an astronomical number.

Radio to MAC Binding:
This technology checks to see that a radio signal is received by a specified network adapter and no other adapter is allowed to receive the signal. This effectively locks the transmission to a specific computer.

Forced Routes:
This technology takes advantage of routing data between access points to connect a sender and receiver. Used in a virtual private network, it insures that data is routed only along a specific microwave path and not broadcast for general reception. Since access points are interconnected with highly directional antennas, the forced route provides a kind of physical security to the radio beam as well as data security along the path using the security measures listed above.

Speed and Range
The speed and range of a wireless LAN is dependent on several factors. Both are inter-related in a complex way due to the electromagnetic properties of wireless signal propagation. Different vendors offer a range of radios and antennas that provide anywhere from 128kbs to 11Mbs service. Generally the greater the distance the lower the speed of the connection. A key factor is the power level of the signal and this is specified both by regulatory bodies and by engineering standards. Systems that provide point-to-point network connections using directional antennas can obtain T1 class speed (1.56Mbs) for up to 25 miles. Airwire.net has installations where T1 speeds are available up to 16 miles away from an access point when directional antennas are used at each end of the link. When wireless is deployed inside a building a major concern are the walls that can reflect or deflect signals. Adapters used inside buildings typically operate from 300-1200 feet depending on interference and building obstructions. Systems also exist that deliver speeds in the 10-15Mbs range for up to 20 miles and operate in the 20-30Ghz frequency bands. These high frequency (millimeter) systems require careful installation and maintenance and are not within the scope of this paper.

Microwave ovens and some types of medical equipment generate radio interference in the 2.4Ghz frequency range and can be a problem. We have also experienced interference with our radio from telemetry equipment that is placed within 6 feet of our antenna. Interference problems can be resolved by re-orienting the antennas or by using special "notch" filters in the 2.4Ghz frequency range.

Vendors and Resources
The worldwide interest in wireless LANs has produced numerous vendors and resources. Below are listed some links to key resources that are maintained by WLANA. We should also expect to see new companies and products introduced into the marketplace as wireless systems become widely used.