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A series of guidelines are presented to help users interested in choosing the best modem for their computer system, and among the factors to consider are the data rates supported by the system, the type and volume of communications traffic and the kinds of lines that will be used. The capabilities of the hardware and the traffic volume are the principal considerations. While full-duplex modems can send and receive data simultaneously, half-duplex devices will either send or receive, and higher speeds can be achieved with echo-cancelling modems than with frequency-division multiplexing modems. Users who frequently transfer large files over public phone networks will easily recover the costs of a high-speed modem through savings in operating expenses.

Permissive and data phone jacks are specified by the FCC Rules and Regulations, Part 68, for connection to the public switched telephone system. Permissive jacks are satisfactory for low data transmission speeds and strong telephone signals but data jacks should be considered for transmission speeds over 2400 bits per second and areas of weak and noisy signals. The article illustrates the two jack type connections and suggests solutions to problems the from using exclusion key telephones and various branch exchanges. CAPTION: (Phone jack arrangements).