5963 computer grade dual triode production dates 3507

It would be correct to say that computerized common control stored program *analog* switches had a short life time, simply because the time lag between development of computers capable of controlling a telephone switch and the later development of an all digital switching fabric was just long enough to make it viable to produce an analog switch controlled by a computer. When the digital switching fabric became available only a decade later the vastly superior technology immediately made all analog switching systems obsolete and uneconomical to operate in most circumstances. (Granted that a great deal of the reason for that was not just the digital switch fabric, but also the vastly more advanced technology for both the controlling computers and for the various peripheral devices too.)

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It was not designed to be an interim product. That just happened to be a fluke of history.

That is all interesting, but in fact the driving force behind the transition from *all* of the various mechanical and electronic analog systems to the modern digital systems developed in the 70's was cost based, but was not equipment cost or depreciation. Labor to maintain them was the significant cost factor. In areas where that labor cost was highest, digital systems almost instantly replaced everything else.

Which is why Alaska, for example, was virtually 100% digital by the mid-1980's, just over half a dozen years or so after the first digital systems were install. At the same time the entire US was only about 33% digital.

Where do you come up with these absurd statements? The first 4ESS was installed in Chicago in 1976, period. The only place it "existed" before that was in the lab and the minds of the people developing it.

In fact, AT&T was caught somewhat flat footed on that one, and the 4ESS had to be a totally new designed to allow use of the all digital network. Bell Northern Research had taken a different approach and designed a previous switch, with an analog network, as if it were a digital network... when the digital network became available they were the first to market simply because it was merely a drop in replacement in their product.

Without a hitch? Go on... It didn't suffer a major shutdown of the entire system, of course. But it was like any other project of that size and scope, and there were *many* local "hitches".

CCIS-6 was first installed in the Bell system starting in 1976.

Common Channel Signaling was developed in the mid to late 60's by the CCITT, and standardized as CCITT No. 6, which was modified by the Bell System and became CCIS-6. (Some CCITT No. 6 was used in the US though, for instance that is what Alascom used here in Alaska.)

CCITT began working on CCITT No. 7, which became SS7, in 1980! It was revised in 1984 and 1988.

1976.

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I'm not sure what your point is, given that virtually *all* offices were converted ASAP.

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