United States to overseas sites. MCI has five public facsimile centers-in New York City, Washing- ton, D.C., San Francisco, Miami and New Orleans-from which the overseas transmissions can originate. The customer can send his doc- ument to one of these centers by facsimile, mail or messenger. One of the more attractive features of this service is that the customer does not have to own a facsimile unit; documents can actually be hand-delivered to the nearest MCI office. RCA Global Communications offers a service called Q-Fax. The RCA service is also geared towards international fax communica- tions. Documents can be delivered to an RCA Q-Fax operation cen- ter via facsimile or in person for over-the-counter service. Q-Fax centers are located in New York City, San Francisco, Washington, D.C., Honolulu, Guam and San Juan. Documents can be sent from these centers to more than 14 overseas locations. GLOSSARY Acoustic coupler. A form of low speed modem that sends and re- ceives data using a conventional telephone handset and not requiring a permanent connection to the line. Analog-to-digital (A-D) converter. A device which converts an an- alog input signal to a digital output signal carrying equivalent in- formation. Asynchronous system. A system employing start and stop elements for individual synchronization of each information character, or each word or block. Attenuation. The difference (loss) between transmitted and re- ceived power due to transmission loss through equipment, lines or other communication devices. Automatic calling unit (ACU). A device which, on receipt of ad- dressing information from a business machine, automatically dials calls over the communication networks. Automatic dialer. A device which will automatically dial telephone numbers on the network. Automatic send-received (ASR). A type of teleprinter with auxil- iary off-line storage that can enable the teleprinter to operate au- tomatically. Bandwidth. The difference between the highest and lowest fre- quencies of a channel, measured in cycles 