Winter 2008 Issue

HSMM

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.
Then we tried moving out of the WLAN channels range but still within the amateur radio band. Some of our WG called this Channel Zero Experiments. Modification of the repeater (access point (AP)/wireless router) frequency and the modification of the client transceiver (PC card) were both required. However, we were dismayed to find that this wasn’t enough of a frequency change. Most standard WiFi PC cards are so broad-banded and unselective that they would auto-associate with Channel 0 gear anyway!
Many other approaches to keeping Part 15 and Part 97 traffic completely separated were investigated. In the end it was concluded that they all added significant overhead to the fledging networks. Either they cost too much, added significant network complexity, or caused a greatly enhance administrative burden, or all of these, thus crippling radio experimentation by Part 97 stations.

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.
While we can, and undoubtedly will continue to debate both the technical and legal questions, it’s clear that what is really needed is for the FCC to clarify the issue. It might even make sense for us to pursue an exception to the rule that applies to transmissions during emergencies. While I understand the logic of not wanting to see the Amateur Service turned into a common carrier for third-party traffic, it makes little sense for millions of Part 15 users to have no restrictions on encryption, while we as Part 97 users cannot provide even basic levels of security when needed to satisfy our served agencies needs.
 

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