Bulletins from the Pacific Packet Radio Society - page 114

Even more surprising is that this diverse group managed to agree on somethings. In fact, the agreement reached on adopting a common link level protocol may prove to be extremely significant in forming the foundation for U.S. packet radio networking. The meeting which originally was supposed to iron out some AMICON details managed to have much more of an impact. He re's some background on what happened:

A year ago, in conjunction with the 181 AMSAT general meeting, Paul Rinaldo organized the first Packet Radio Networking Conference which was held at the NBS in Washington (some excellent conference proceedings are still available). Many ideas and some real and paper networks were discussed. In the months which followed quite a few people got their packet radio controllers running and had a chance to experiment, read, discuss and think about various problems involved in implementing PR networking. The situation became discouraging. It seemed like a new protocol was proposed for each TNC that came on the air. Each group started heading off in a different direction. The promise of compatible systems grew remote.

But in this dispersion of effort people also found out how difficult it was to implement private protocols and how difficult the interconnection would be if common ground wasn't found. The different groups also came to realize that there was a common set of problems to be solved and that one area's solution couldn't ignore the requirements of other users. The summer doldrums saw very little activity and not much progress, and provided the background for the AMSAT meeting.

The AMICON Network

Two major areas of concern filled the agenda of the AMICON meeting: the modulation method to be used for the Phase IIIB special service digital channel, and the protocol to be used for linking two ground stations via the satellite.

There was a lot of discussion on the modulation method, and Den Connors and Lyle Johnson of TAPR and Paul Rinaldo of AMRAD presented their research findings. Many different modem types were re vie wed and international requirements we re discussed. After all the debate the following conclusions were reached:

1. The L1 SSC will be restricted to 5 kHz bandwidth (at the 26 dB points). Modem performance is a primary consideration for a groundstation, and the modem used will probably be of a fairly advanced design.

2. The use of 202 modems using NBFM-AFSK will not work.

3. The use of 202 modems using SSB-FSK will produce marginal results.

4. A 1200 bps channel speed is probably optimal, as this speed satisfies a variety of different constraints and requirements.

5. The BPSK modulation method developed for IIIB telemetry should be explored at both 400 and 1200 bps.

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