Physical Links Public key and other crypto techniques have been discussed here. So has TEMPEST shielding against eavesdropping. But, there hasn't been a discussion of physical data link options (unless it was "before my time"). IMHO, this topic should have a place in the FAQ. m. Physical Data Links. a. Telco/Dial-up b. Radio 1. VLF 2. MW (near Broadcast AM) 3. Shortwave 4. VHF 5. UHF 6. Microwave c. Infrared/Visible Free Space d. Laser/Maser Beam n. Modulation Techniques. a. AM b. SSB c. ACSSB d. FM e. SSTV f. FSTV g. Spread spectrum (hybrids of the following) 1. FH - frequency hopping 2. DS - direct sequence 3. TH - time hopping 4. TR - transmitted (noise) reference 5. SR - stored (usually pseudo-noise code) reference o. Network elements (?) 1. Wire and cable (underground, disguised) 2. Point-to-point (radio) 3. Simple repeaters/linear translators (transponders) 4. Regenerative repeaters (digital packet) 5. Satellites 6. Meteor scatter 7. Moonbounce I'd like to see pro and con discussion of these items. Having encrypted messages won't do any good if Our Enemy simply pulls the plug at the telephone company. Kent - kent_hastings@qmail2.aero.org. #000#