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If you could make one good invention in the telegraph, you would secure an annual income and then you could settle that on your wife and teach Visible Speech and experiment in telegraphy with an easy and undisturbed conscience.
Excerpt from a letter dated March 13, 1876, to Alexander Graham Bell from Gardiner Hubbard, Bells future father-in-law.
In the beginning, there were only telephone sets and wires between them. The first commercial sets, offered by the Bell Telephone Company in May 1877, consisted of a single piece of wood (black walnut or mahogany) with a single piece of equipment serving as both transmitter and receiver. Power was supplied by a permanent magnet contained within the device, rather than by a battery or external power source. Each telephone set was connected to another set directly through a private line, which generally was leased from Western Union. The first advertisements offered the use of two telephones, and a line connecting them, for $20 per year for social purposes and $40 per year for business; free maintenance was guaranteed. By the fall of 1877, over 600 telephones were in use. As the popularity of the invention grew, visions developed of rooms full of telephones and skies full of wires [4-1].
In order to improve the usefulness of the telephone device and in order to reduce the associated costs, circuit switches were developed. The first practical exchange switch was developed by George W. Coy of New Haven, Connecticut and was placed into service on January 28, 1878. This manual exchange, or cordboard, allowed the flexible interconnection of 21 subscribers. The number of exchanges grew quickly, although most of the initial installations were Western Union, rather than Bell; the Bell System network grew quickly and soon outpaced the networks of Western Union and other providers [4-1].
These first exchanges, which were housed in central offices, allowed circuits to be manually connected, on demand and as available. Through these central points of interconnection, each subscriber required only one terminal device and one wired connection. Central Office Exchanges (COs or COEs) handled all switching of calls, even calls across the hall or between employees in the same office were connected in this manner. When such exchanges were automated, it remained clear that this approach was less than ideal for serving businesses of any significance and with any appreciable number of terminal devices because of the following factors:
Clearly, a better approach would be to extend a partition of the Central Office Exchange to the customer. The equipment could be rented by the customer, yielding additional revenue to the telephone company. Additionally, the cost of labor, cost of switch capital, and responsibility for connection errors could be shifted to the customer. Further, the customers operators could provide more effective and personalized service to both inbound and outbound callers. The equipment could also act as a contention device, allowing multiple calls to share a single, pooled set of local loop connections. This approach would considerably reduce the cost of cabling and the number of ports required to connect the local loops to the switch. The shift to the customer of the responsibility for switching calls would also relieve the telephone company of that burden, allowing the telephone companys exchange switch to serve even more customers. Finally, internal (telephone-to-telephone) calls can be connected through the customers equipment, without having to connect them through Telcos Central Office.
The first devices to accomplish this feat were Private Branch Exchanges (PBXs) in 1879. Key Telephone Systems (KTSs) did not arrive on the scene until 1938. Centrex, a central office-based solution was christened in the 1960s. Automatic Call Distributors (ACDs) appeared only recently, in the 1970s. Rather than exploring these systems in chronological order, I will begin this discussion with KTS, as it is in many ways the least complex. I will then progress through PBX, Centrex, and ACD systems. This chapter will conclude with Computer Telephony Integration (CTI), a concept that only very recently has translated into application software products which put system control in the hands of the user.
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