How does the Master communicate with the Remote Terminals ?
You may select one or mix of several means of communication. They are leased telephone lines, standard dial up telephone lines, cellular telephones, or UHF-VHF radio. Your selection will be based primarily on cost and circuit availability. Leased Lines are reliable and require less initial investment in equipment. If data is required in real time, perhaps every few minutes, the leased line is often specified. There is a monthly fee for the line use, charged in mile increments. The Bell compatible 202 Modem is the industry standard for these circuits. Key manufactures a full line of 202 modems for both the Remote Terminals and Master Station. Dial Up Lines are well suited when the data needs to be accessed less often. Again the investment in equipment is low and the telephone rates are about $50.00 per month for each site, plus long distance charges. The modem used here is the CCITT standard, the same unit that is supplied in virtually every personal computer. Key uses an off the shelf
