Private Line Services:
I know that this will represent "ancient history" to some readers, but here goes.
Beginning probably in the 1960s (before my time there) American Airlines (AA) had what was called a "customer controlled switching arrangement", or CCSA with AT&T. Of course, they were the only game in town in those days. AA eventually had almost 150 locations "on net".
In retrospect, the CCSA was a predecessor to the "software defined network" that was introduced by AT&T, Sprint and MCI in the late
1980s.At any rate, the CCSA allowed a company to lease private lines (full period, no per-minute charge) between the AT&T switching centers, with Centrex-like phone lines to the various AA offices. I don't know for sure, but I expect the switches were the Western Electric 4E tandems. Since calls were not charged per-minute rates the network was cheaper to operate than just using direct dial. AA was also one of the first companies to take advantage of WATS (wide area telephone service) for calls to about 14 or 15 reservations centers. Foreign exchange (FX - a type of private line) service was used to serve cities where AA flew.
In the early 1970s Collins Radio developed the first automatic call distributors (ACD) for use outside the phone company. Unknown to most people, AT&T had developed their own ACD for internal use, and possibly for customer use as well, some time before that. I have a Bell System "Traffic Facilities Practice" dated May 1965 in my files. Their "service level" objective was 93% in 20 seconds, or an average speed of answer in 4-6 seconds.
The Collins (later Rockwell) GVS-750 ACD was equipped for 1,024 ports and was originally designed for the hospitality industry - airlines, rental cars, and hotels. AA installed five ACDs in four locations (Hartford, CT, Cincinnati, OH, Dallas, TX, and Los Angeles, CA. The previous 14-15 reservations centers were consolidated into these four locations. A combination of foreign exchange (FX) and WATS lines was used to route customer calls. FX was used for cities where AA flew, and banded WATS was provided for other locations. There were numerous WATS numbers in order to keep them in band 3 or less, due to the relatively high costs at the time. A full-period (240 hours per month) band 5 WATS was about $3,500 per month, if my hazy memory is anyway near correct. In today's environment $0.25 per minute may seem astronomical, but we are talking 1970s here.
The original design thinking at Collins was that there would be about a 2:1 ratio between incoming lines and agent positions. From a traffic engineering standpoint that would be true if there were lots and lots of small trunk (FX) groups. In actual practice, we used much larger groups (some up to 100 circuits) so our ratio was more like 1.2 or 1.3 lines (FX plus WATS) to one agent. This left a lot of unused ports on the ACD.
In about 1976 AA hired some people who came out of the military and had been trained by AT&T/Bell as part of a "training with industry" program. They saw the possibility of building a private network of private lines using the "spare" port capacity in the ACDs for tandem switching. I came out of the Army, having had the same AT&T/Bell training a couple of years later than the original guys. When I came on board in 1978 we were well along with the transition. Of course, by that time MCI and Sprint (OCCs, or other common carriers) were offering private line service a lot cheaper than AT&T, so we spread out our service based on cost. There were other issues, such as circuit order delays with the OCCs (AT&T did everything they "legally" could to delay interconnection at the operating company) and some of the OCC circuit quality was not as good. We had a lot of trouble early on with rain/fog fade on MCI microwave circuits until we convinced them to install quad diversity.
At any rate, we got our private network installed, and one of my jobs was to analyze the traffic each month and make adjustments to circuit counts. We developed an internal analysis system to base provisioning on cost/benefit, rather than on the traditional mathematical Poisson or Erlang B traffic formulae. All of the inter-switch trunks were four-wire, and we used overflow and diversion techniques to balance incoming customer calls among the call centers.
We used the FX circuits into the busier cities for "tail end hop off" for corporate long distance calls. If a call was going to an off-net location we routed it to the nearest tandem switch and hopped it off to the PSTN at that point. By about the mid-1980s our network average cost was running about $0.13 per minute. This was when a direct-dialed PSTN call averaged about $0.25 per minute. We were also using "time assignment speech interpolation" (TASI) equipment that would carry 31 voice paths on 16 private lines. (FYI, TASI was invented in the late
1950s to increase the capacity of TAT-1, the first trans Atlantic telephone cable).In the late 1980s AT&T introduced the Software Defined Network (SDN) and AA took advantage of the newest offering from AT&T (Tariff 12, it was called) and we migrated the entire corporate network to AT&T. The marketing department was quick to soak up the capacity on the ACDs that we had been using for tandem switching, so we were still making maximum use of the ACD capacity.
By the early 1990s I was managing the network and AT&T would not respond to my requests for certain services -- but they thought they had a "lock" on our business due to the commitments we had made under the Tariff 12 agreement. We had enough "slack" in the economics so that I could move the corporate network -- which I did. We kept the reservations service with AT&T, which by that time was all based on nationwide 800 service (the new name for WATS), but I took the corporate network to MCI's Virtual Private Network. AT&T never invited me to any "outings" after that, but we saved a pocket full of money by doing it my way. The network average cost was down to about $0.08 per minute.
I moved on to other work in 1998, but when I was "invited" to leaveAA/ Sabre in 1999 the VPN was still working. I do not know what happened after Sabre was sold to EDS and the world revolved again.
Private lines may still have a place -- it just depends on your business. For instance, some alarm companies lease "dry pairs" from the alarm premises to the monitoring station. They are still useful where you want to load-balance between call centers, or have to do call transfers to another location. They are still leased (I think) by the quarter-mile, based on the airline mileage computed using the V&H coordinate system.
Regards,
Charles G. Gray Senior Lecturer, Telecommunications Oklahoma State University - Tulsa (918) 594-8433
[TELECOM Digest Editor's Note: Since commercial long distance has gotten _so_ inexpensive in recent years, I cannot think of a single instance in which a 'private' network would be more economically viable these days as an alternative. However, many companies and other institutions continue with private networks out of, IMO, a misplaced sense of security, i.e. if the local central office burned down (its been known to happen) or there were other commotions (again, also known to happen) "then we would have our private network to fall back on". But would they really? Time and again, those 'private networks of any size and/or consequence are routed over the very same wire pairs and through the same central office equipment as the 'exposed and open to danger' lines of the company's "regular" phone service. After the May, 1988 fiasco in northern Illinois with the central office fire in Hinsdale, Illinois, people at first were saying "Well, thank God I have my cellular phone"; or "We can always use our private system in the office to reach other cities, etc." I am afraid that was not the case. Those lines were down and out for the duration also.So these days, do private line networks make about as much sense as 'banded WATS lines'? How many ways can one pinch a penny? PAT]