A Bridging Strategy

A Bridge Too Far?

The first question you need to answer is simple: Can you cross the distance you need to bridge with equipment that you can afford? Several parameters affect the viability of a Wi-Fi network bridge, but the overwhelmingly largest one is simple distance. I spend the last portion of Chapter 8 discussing the notion of a link budget, which is how you determine when your network bridge is a bridge too far. Definitely read that section of this book now if you haven't done so already.

Briefly summarizing: You begin with a stated amount of radio power from your bridging access point. You calculate the loss inherent in the path you want to bridge, and add to that any losses in coaxial cables and connectors on each side of the bridge. You must balance that loss to some extent with gain in antennas on both sides of the bridge. It cooks down to this kind of an equation:

Input power (dBm) + total losses (dB) + total gain (dB) = received signal (dBm)

You end up with a received signal figure in dBm, which is the power delivered by the remote antenna to the receiver of the access point on the far side of the bridge. If this received power figure is greater than the sensitivity of the access point's receiver, your bridge will work. If it's less, your bridge will not connect. If it's barely sufficient, your bridge may connect, but the bit rate across the bridge will be low (perhaps 1 or 2 Mbps rather than the top bit rate of 11 Mbps) and you will lose packets to noise, fringe ('Fresnel zone') obstructions, reflections, interference, and 'unknown causes.' Ideally, your received signal figure needs to be 20 dBm above the receiver's sensitivity figure to connect reliably at the top Wi-Fi rate of 11 Mbps.

So before you begin, take a flip back through Chapter 8 and do the math. Just to scare you a little bit going in, the path loss across a one-mile path is 104 dB.

This isn't a slam-dunk, whatever else you may have heard.