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Infrared. Infrared communications require line-of-sight transmission over a limited bandwidth. For example, InfraLAN uses an optical wavelength of 870 nanometers; its range between nodes is 80 feet. Hence, a potential intruder must be in the office within the specified range and must be in a line-of-sight path, a combination of factors that can be easily achieved only by insiders.
The use of infrared technology is not licensed by the FCC. This increases the possibility of unauthorized use and potential interference. However, this technology is also relatively secure because disruption of its line-of-sight operation (e.g., in the event of electronic eavesdropping) will bring the LAN down. In light of the limited distance between nodes and the line-of-sight requirement, infrared-based wireless LANs are considered relatively secure.
Radio Frequency. Although radio frequency transmissions can pass through walls and partitions, radio frequency networks must usually be kept on the same floor. Because line-of-sight transmission is not required, transmitted data can be more readily intercepted. To combat this problem, some products have incorporated encryption capabilities.
By sending data over several frequencies, spread-spectrum transmission minimizes the possibility of eavesdropping. Radio frequency-based LANs currently use frequencies in the range of 902 MHz to 928 MHz. The drawback of these frequencies is that they are also used by television, VCR extenders, and antitheft devices in stores. In the presence of such devices, the network may be disrupted. Generally, radio signal is affected by noise and interference.
WaveLAN is one product that uses spread-spectrum technology. In an open environment, it can cover a range of 800 feet, and in a semiclosed environment, it can cover a range of 250 feet. Because radio technology is well understood by many professionals, it may also be more susceptible to attempts at unauthorized access. This exposure can be mitigated by implementing such security mechanisms as encryption and access controls.
It should be noted that the IEEE 802.11 committee is trying to forge a standard radio frequency for use in network transmissions.
Microwave. Microwave is a communications technology used to connect LANs between buildings and over greater distances than is possible with infrared or radio frequency technologies. Altair uses microwave technology; this product is compatible with existing cable-based standards, protocols, and communication speeds, and can complement, replace, or extend such networks as token ring and Ethernet networks. One of Altairs strengths is its transparent operation with Ethernet architecture and such NOS as Novell NetWare and Microsoft LAN Manager. Altair utilizes the FCC-licensed 18GHz frequencies, and it can cover a range of 5,000 square feet. To coordinate the use of separate frequencies, Motorola has established a centralized Altair Frequency Management Center to ensure compliance with FCC regulations.
Altair provides two built-in security features: data scrambling and restricted access. The data scrambling feature scrambles data between the control module and the user module. The restricted access feature, which is incorporated into Altairs Time-Division Multiplexing architecture, allows access only to user modules whose 12-digit IEEE 802.33 Ethernet addresses have been entered into the control modules registration table.
Because microwave use is FCC-licensed and, hence, is monitored, it is considered the most secure system. As one might expect, potential intruders tend to avoid regulated environments for fear of being caught and prosecuted.
For a complete understanding of the security concerns affecting wireless LANs, the concept of service availability must be understood. In a simple way, service availability can be thought of in terms of the dial tone one gets when picking up a phone the absence of a dial tone can be the result of equipment failure, a busy circuit, or a poor signal.
Service availability can be discussed in terms of these three components: signal availability, circuit availability, and equipment availability. To tap the network using unauthorized terminal connections, the perpetrator must obtain an adequate signal, an available circuit, and the right equipment. If any of the three components of service availability is missing, access to a wireless LAN cannot be completed. However, having service availability does not automatically mean getting successful access to the network. Other factors such as network architecture and network security mechanisms affect the potential success of access attempts.
In a radio frequency system, signal availability has to do with whether there is sufficient radio energy reaching the receiver to produce an acceptable bit-error rate in the demodulated signal. In an infrared system, the receiving unit must be in the line of sight of the beam. Signal availability directly relates to distance; as a node is placed beyond the effective range, the signal becomes unavailable.
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