Winter 2008 Issue
The Hinternet Protecting HSMM Radio Networks
By John Champa, K8OCL
The 2.4-GHz (13-cm) band presents some unique challenges to HSMM (High Speed Multimedia) radio amateurs. Not only do we share some of the same frequencies (Wireless LAN channels 1 through 6 are within the amateur band), but also we almost always use the same modulation type, IEEE 802.11b/g.
In the years that the former HSMM WG (Working Group) negotiated with the FCC Enforcement Branch via the ARRL’s highly experienced attorney, we experimented with many different approaches to avoiding auto-association with Part 15 unlicensed stations. We knew that was one form of communications the FCC did not want to see happen except in the case of an emergency.
What was needed is some effective method of communications isolation or protection called authentication. This would immediately identify the Part 15 stations and also immediately restrict them from entering into our Part 97 networks.
First we tried cross polarization. Most Part
15 stations use vertical polarization, so we thought horizontal
polarization would provide isolation. That helped somewhat, depending on
the situation. However, not all Part 15 stations use vertical
polarization, and the multi-path effect causes many polarization shifts
that negate the expected isolation.
The WG finally came to the conclusion that the very methods built into the modulation protocols themselves (WEP, WPA) held the solution. Yes, these are primarily encryption methods, but they also very efficiently and cost effectively provide a poor-man’s authentication method. However, the intent is not to obscure the meaning of the transmissions, only to protect the network. With your callsign always in the clear (service set identifier, or SSID), the encryption published and standardized, plus the key recorded in your station logbook, this should be evident to all.
As Les Rayburn, N1LF, Shelby County, Alabama ARES EC recently wrote to me regarding this struggle within:
Like many, I’ve sat on the sidelines trying
to make sense of this hot-button issue: Encryption, especially as it
applies to HSMM radio, seems to attract both the best of our technical
minds, and the worst of our “barracks lawyers.” As an amateur whose
primary interest is in emergency communications, I can tell you that
security is something that served agencies are concerned
about—especially when you’re dealing with hospitals and at the federal
level, where the Privacy Act seems to creep into almost any discussion.
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