The Fade Margin is an additional level of required signal strength assumed during the design of a wireless network that provides an allowance for signal strength fading in the final installed network. This design allowance provides sufficient system gain or sensitivity to ensure that the required quality of service is maintained even if environmental noise, co-channel interference, reflection, refraction, diffraction, or other signal attenuation issues are present. It's typical to add a 10 dB fade margin to a wireless network design. Hence, if the design specified equipment requiring a minimum -85 dBm signal level the RF engineer would design a system based on a -75 dBm signal level, applying the 10 dB fade margin to the system.

A firewall is that part of a computer network that implements and enforces an access control (or security) policy between two networks. The software that performs the assessment and enforcement can execute in a general purpose (stand-alone) PC or server but, very often, the software is optimized and sold as a firewall appliance. Hardware manufacturers like WatchGuard, SonicWALL, and Symantec (just to name a few of the many in the market) build a device that has Ethernet ports and acts like a router and/or switch and provides the firewall functionality. This type of firewall appliance if commonly, and simply, called "A Firewall". Firewall functionality can also be implemented in software alone. Like Norton Personal Firewall, software typically offers less types of protection and fewer connections since it must run on a PC or server and not in an optimized, dedicated chassis. Firewalls usually guard an internal private network from an external public one, isolating an intranet from the Internet. This is referred to as inbound protection. Traffic can also be evaluated as it flows out of a private network. An Egress Firewall or a firewall offering outbound protection can prevent malicious code hidden in an email or brought in on a user's home notebook computer from contacting its home program across the Internet. Essentially a firewall connects two or more networks but only allows specified forms of traffic to flow between them. The firewall is a means by which a security policy can be enforced.

When used in conjunction with the design of a Wi-Fi wireless network the access points are connected into a backhaul topology (typically Ethernet switches and/or routers) in such a way that no physical connection is made between the access point infrastructure and the private network. Both the access point infrastructure and the private network then connect to the firewall which, in turn, is connected to the Internet. The firewall's security policies protect the private network against unauthorized access by wireless users.

(Pronounced FRA-NEL) Practically speaking, the Fresnel Zone is a volume around the line-of-sight line between two RF antennas within which obstructions will degrade the strength of the signal. The Fresnel zone can be visualized as an oval that has been rotated into three dimensions about the axis of the line-of-sight between the two RF antennas. The radius of the Fresnel Zone is largest at the midpoint between the antennas and smallest at the end-points (at the two antennas). The radius of the Fresnel Zone at the midpoint between the two antennas is given by the formula:

..where h is the radius of the Fresnel Zone in feet, L is the distance between the antennas in miles, and F is the frequency of the RF signal in GHz.

A common guideline is that the Fresnel Zone must be at least 60% clear of obstructions, so the 72.1 multiplier in the above equation is commonly substituted with 43.3 to give the 60% radius of the Fresnel Zone.