5963 computer grade dual triode production dates 3506

Davidson)

Correct, which is why they had such a short life span. What the 1A did was allow various buttociated companies with depreciation schedules favoring retaining fully amortized equipment to finally replace the last panel and SXS exchanges while waiting to see what would develop for full time-space-time local swiching. The 1A improved end office performance and allowed exchange companies to offer unregulated features while cutting power and maintenance costs dramatically while retaining analog interface with existing short haul analog carrier systems without expensive conversion. It was an interim product at best, and the 5E conversions that came later were simplified by already having the end offices "groomed" for ESS. California was one such state in which equipment depreciation rules allowed for retention of both switching and facility equipment long after it was gone everywhere else, which is why SXS offices lasted almost to the '80s and 40 year old tube driven N-CXR systems still carried local toll tandem traffic. GTE retained SXS even longer, since their 1-EAX machine was problematic at best and their comparative lack of resources made waiting for the GTD5 to seem the logical move. Service in those offices was abyssmal, forcing GTE to deploy the GTD5 ahead of schedule with attendant problems along the way.

4E was around long before that. The CHCG01 cutover was the first of a wholesale multibillion dollar 4A replacement project that lasted through the '80s. It was the largest switching conversion project ever attempted worldwide and it came off with nary a hitch.

Although all production 4Es came with CCIS, wholesale conversion of the network didn't really get done until the around 1980. All in place 4A-XBAR machines were converted to CCIS by around 1980, with in-band signalling still left for interface with independents which did not convert at the time. Toll fraud was rampant in the '70s ("phone phreaking" had become something of a national pastime) and a multi-million dollar cost factor, which put the impetus behind conversion of end-of-life XBAR machines to CCIS. The cost-benefit analysis of the 4A CCIS implementation showed that, although remaining 4As and 4M tandems that were converted would probably be gone in two years or so, the savings in toll fraud costs would amerliorate some of the project cost, as would savings by shutting down all 17C message testboards and elimination of SF equipment maintenance and repair. Local toll XBTs stayed with in-band signalling until replaced, since local toll fraud wasn't as huge an issue at the time in comparison, as LD revenue was basically subsidizing local and local toll costs. During that period, all remaining short haul analog carrier facilities were replaced with T-CXR, thus allowing the 5E project to begin.

'93, as I remember it. Comparatively few new offices have been built since.