The document discusses various communication channels including telephone lines, coaxial wire, fiber optic, microwave, and satellite. Telephone lines have been used for voice and data transmission for years using twisted copper wire pairs and phone jacks. Coaxial cable has a greater capacity than phone lines using a single copper core. Optical fiber transmits data as light pulses through glass tubes, having an even greater transmission capacity and being immune to interference. Microwave networks transmit radio waves through the air over short distances, while satellites orbiting 35,400 km above Earth can transmit large data volumes by acting as microwave relays.

1. Communication Channels