Radio E-Mail in West Africa
Editors' Note: The complete version of this article, was later published on the Linux Journal web site.
Deep inside the warm green interior of Guinea, centered in the frontal lobe of West Africa, international rescue workers in the widely scattered towns of Dabola, Kissidougou and Nzérékoré now enjoy regular internet e-mail, delivered straight to their own desktops. There isn't a telephone line or satellite dish in sight. Instead we are moving the mail over distances of hundreds of miles—over jungled mountains and high palmy savannahs—using high-frequency (HF) radio. Our project is called Radio E-mail, and here is its story.
The Republic of Guinea is a cashew-shaped nation on the Atlantic, ten degrees north of the equator in West Africa. It is a beautiful and resource-rich nation, about the size of Oregon. As far as African countries go, Guinea is a calm pocket of peace and stability and generally doesn't attract a lot of attention. But Guinea quietly has played a heroic role in the theater of world events in recent years, providing a safe and welcome refuge for as many as half a million people displaced by brutal wars and civil upheavals in the neighboring countries of Sierra Leone and Liberia.
The International Rescue Committee (IRC) has one of their largest operations in Guinea, providing services and support to a population of up to 200,000 refugees in many camps established throughout the country. I became involved with IRC when my wife accepted the position of country director for the program in the summer of 2001. Soon we were traveling on an inspection tour of the camps, making the long road trip to visit the program's three field offices “up-country”.
Traveling outside the capital city of Conakry, one immediately finds that Guinea has little infrastructure, especially in the way of electrical grid and telecommunication systems—to say nothing of broadband access to the Internet. So IRC field offices must provide their own infrastructure: diesel generators for electricity and HF radio sets to communicate with other offices and mobile units, which can be up to hundreds of miles apart.
Expecting this isolation and general lack of connectivity, I was quite astonished to find a radio operator using his equipment to make a binary file transfer from his desktop PC to another field office—wirelessly! On top of the operator's radio set, connected to the serial port of his PC, sat a dingy black box labeled “9002 HF Data Modem”. The operator used a proprietary, MS-DOS-based program to make his file transfers, but I immediately began wondering. If this device is moving binary data over the ether of radio, why couldn't we set it up with Linux and network with PPP connections as well?
Since IRC owned most of the equipment already and because we would be using Linux and other freely available software, the system could be implemented at negligible cost. I developed a design and specification for the system, and the project we call Radio E-mail has been continuously operational since January 2002.
If you have been making the move to wireless lately, most likely you are working with the microwave, high-bandwidth frequencies of 802.11b. If so, you know that on a clear day you maybe can get a line of sight connection out ten miles or so. HF radio is another animal. Its longer waves reflect off the ionosphere to follow the curvature of the earth, giving HF signals a range in the hundreds of miles. From Conakry to Nzérékoré (IRC Guinea's most distant field office), HF easily covers a straight-line distance of over 375 miles (600 kilometers).
So the great advantage of HF is it can go the distance, leaping the obstacles in its path with aplomb. Now for the bad news: where HF wins the wireless game in range, it loses its pants in data capacity. If 802.11b is considered broadband, think of HF as slim-to-none-band. The radio modems we are using here are spec'd at an anorexic 2,400 baud!
And wait, it gets worse. Two-way radio is the classic half-duplex medium of communication. That is, you are either transmitting (push to talk) or receiving, not both at the same time. This, plus the robust error-checking protocols implemented by the modem hardware, means the actual link experience is more on the order of 300 baud. Does anyone remember 300 baud? Unless you measure your patience with radio-carbon, your dreams of remote login sessions will be dashed and splattered.
However, for classic store-and-forward applications like text-based e-mail, the bandwidth limitation of HF radio is workable. We do need to pay close attention to our configuration and try to optimize as much as possible. With HF radio, every packet is precious.
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