Swift Fox Blog

Jan 2014

802.11 Hidden Node, how to fix it

The hidden node problem in wireless arises from a faulty way of devices talking to each other.  This causes a lot of network collisions.

Simply put, collisions are when two network devices try to talk at the same time.  This is bad, as it means that the receiving end can’t understand what just happened – and both senders have to try again.  It becomes especially troublesome at prime-time as more clients are attempting to use the network simultaneously, and collisions are often the primary cause of prime-time slowdowns.

CSMA: The default won’t work for WISPs

802.11-based equipment is great because of its low cost and wide compatibility, however the protocol was never designed with long-range WISPs in mind.  It was designed for a coffee shop or home environment.   By default, 802.11 uses a scheme called “CSMA” (Carrier Sense Multiple Access) to avoid collisions, which works as follows:


  • Client: “I don’t hear anyone so I’m going to talk now”.

This works great in coffee shops because each device can hear every other device – they’re all using small omnidirectional antennas.   With long range WISPs, all the clients have very directional antennas and because of this they can hear the access point (AP) but not each other. This means when they listen using CSMA, they hear nothing, so they can always talk.  From the AP’s point of view, everyone is talking at once, so it constantly has to say “try that again” (aka. “retransmit”).   This situation where an AP can hear a device but nobody else is able to, is called “hidden node” – because the node is hidden from other clients.

Standards-based solution: RTS/CTS


Author: Matt Beaton

Dec 2013

Considering a new business idea?  How about a WISP?

Considering a new business idea? How about a WISP?

Who needs you the most? Places without broadband at all!

When most folks think of ISPs, they think of the cable company and the phone company – and they don’t have a great reputation.   As an independent Wireless Internet Service Provider, you have the chance to challenge that – and provide an awesome service for a reasonable price.  But people will be skeptical at first, or they might be on a contract and can’t easily switch providers.

When starting a WISP the first thing to go after is the highest density of homes that have no option at all besides dial-up or satellite.  To be honest, there aren’t many of these markets left – they’re becoming very rare.  But if you can find this mythical market, you have it easy.  Nobody likes dial-up, and satellite is laggy and expensive.

How do you find these places?  Unfortunately, the best option still seems to be to drive around and ask people.  Ask at the local computer store, gas stations, or if you have friends in the area.  If people are stuck with dial-up, they’ll be very excited to help you start a WISP bringing broadband to their area.

Do not trust the excited local who insists there are no options in their area.  They have not done all the research and even if they claim “I know everyone!” they may not have been asking the right questions or they may have honest but ulterior motives.  Where to open coverage is one of the most important decisions faced by an ISP, don’t cut corners or leave it up to others to do the research.

Competing against another WISP:  Doing it better for cheaper

More likely than the above, you’ll be i

Author: Matt Beaton