This is an article written by a fellow ham radio operator. Reposted with written permission.
Packet Radio
By Frank Wolfe (NM7R)
Packet radio is a product of the early 1980’s. “Packet switching” was being developed then, as part of work on DARPA-net, the prototype of the Internet. Some of the folks working on the project were Hams, and adapted packet switching to Amateur radio. Packet radio is a way of transferring text information from one computer to another, using Amateur radio.
During the 1984 Summer Olympic Games in Los Angeles, CA, a packet radio demonstration project sent the scores across the country to New York in real time. Each “packet” of digital information contains a “to” address, a “from” address, any intervening addresses, a block of text, and an error-correcting check-sum.
The Internet has matured quickly into a faster, broader, more ubiquitous medium. Using fiber-optic connections bandwidth is capacious. Packet radio, by contrast, has remained hobbled by the narrow bandwidths available on Amateur radio frequencies. So, instead of MegaBits per second, packet radio is limited (on VHF) to 9600 bits-per-second. In fact, most popular packet systems operate at the relatively glacial pace of 1200 baud, in order to pass through unmodified audio circuits intended for the human voice.
Over the years, Packet Radio has proven its worth, however, in Emergency Communications (EmComm). The built in error-correction ensures that a message is received perfectly, or not at all. The long range of VHF signals allows packet radio to span tens-of-miles between “nodes”, making a network relatively inexpensive to construct. Like most Amateur radio EmComm solutions, the technology is “narrow” but reliable.
Just as an Amateur push-to-talk voice circuit is very limited compared to the Public Switched Telephone Network, a packet circuit is only a shadow of an Internet email terminal. But, when a disaster knocks out the normal commercial means of communication, either is a valuable asset. When looking at a commercial infrastructure reduced to the Stone Age, having a 1200-baud digital text channel available looks pretty nice.
A characteristic of packet radio that is different from, say, VHF voice, is that any packet station in the network can generally be used as a repeater. This allows signals to be relayed long distances. If a particular relay station goes off the air, the packet path can possibly be routed around, through one or more other stations.
In recent years, the
Winlink2000 project has refined the interface between packet radio and the Internet, allowing a message originating on an isolated computer to be transferred over an Amateur radio circuit to a Remote Message Server station in an area with operational Internet service. From there, the message can be delivered over the Internet connection as regular email. A reply is also possible, taking an email message off the Internet and relaying it as plain text to the isolated computer. Just as the one-eyed man is king in the land of the blind, a packet circuit out of a devastated area can be a lifeline.
Many of the perceived limitations of EmComm are illusory. Generally, in a real emergency, the actual number of messages is small. However, the importance of each one becomes large. It is much more important to deliver each message accurately and efficiently, than to have a capacity for large numbers of messages. EmComm providers do a disservice to their “customers” when they ignore maintaining robust but simple systems in favor of fancy new “sexy” technology that may be more vulnerable. Remember the “kiss” system; Keep It Simple, Stupid.
A complete packet station can easily fit in a briefcase or small backpack. Unlike a voice repeater, the equipment is compact, inexpensive, and easy to deploy. Most messages are easier and faster to send with packet versus voice, and the longer the message, the more this is true. Long lists are particularly suited to packet transmission.
There is even a measure of privacy afforded by the requirement that an eavesdropper would need a TNC or sound-card program to decode the over-the-air tones. Although nothing on Amateur radio can be “secure”, this does reduce the number of folks listening. Caution: for medical information, packet does not meet the Health Insurance Portability and Accountability Act (HIPAA) standard of confidentiality.
de NM7R
ARES SEC WWa
