Re: [Telecom] 11X and N11 Codes (was 911 not universal)

But even Bell SXS areas which had originating customer DDD in the
> later 1950s also used 112+. It's just that GTE and other independent > telco areas retained using 112+ and other 11X codes longer than Bell > SXS areas did.

I know of Bell SxS exchanges in major metro areas that retained 11n codes as late as 1970.

A review of telephone directories of small towns at that time showed a great variety of codes, some rather complex.

Let's remember that changing codes was not merely feeding in a new mag tape generic into the system. It meant planning an announced cutover, doing a cutover, and manually adjusting each selector and other gear to work under the new coding scheme. This required engineering planning. Lastly, customers had to be educated about the new dialing instructions. All of this meant substantial cost to the company.

Complicating the issue were normal growth of traffic and new features such as Touch Tone or DDD. I would suspect stable areas wouldn't get changed until very late while growing areas would get changed at the same time new gear was added to the office.

Yes, 11X codes were introduced for SXS areas with the 1920s, while > N11 codes were introduced for Panel areas with the 1920s and those > Panel-dominant areas were the ones to add #1XB with the later 1930s. > And yes, Panel and Crossbar areas COULD use 11X codes if necessary.

There was a concern (I don't understand) the candle stick phones of that time would sense an erroneous pulse that would confuse SxS gear, thus the 11 code. Why this wouldn't screw up panel gear I don't know. Once 'sticks went away the issue was moot.

The 110 code for the Long Distance Operator in Step-dominant > locations was usually abandoned, that function being combined with > the local '0' Operator.

Operators could be centralized and given more efficient boards as time went on. Toward the end of the cord era they developed a computer assist for cord boards, a keypad and numeric display replacing the old row of keypulse buttons. I believe this brought AMA in so the operator didn't have to wrte up a ticket and start/stop timing. It may have automated routing as well. (Anyone who knows more please share it with us).

Photos of cord operators in 1970 shows most of them filling out the toll ticket, not switching calls. Being able to enter called and calling number via keypad and automate timing was much faster than the mark-sense coding (plus the called number had to be keyed in anyway).