Re: Touch Tone at 1964 World's Fair [telecom]

Jul 12, 2008 Last reply: 18 years ago 2 Replies


No, panel didn't make there. Los Angeles was a special case,


> apparently from a mixture of companies, and was step-by-step. I don't
> know the history, but I believe some efforts at a 'poor man's common
> control' was applied to their SxS.

The Los Angeles area had a variety of telephone companies. Two which come to mind, besides the Bell company, were the Sunjand-Tujunga Telephone Company and the California Water and Telephone Company. There were so mamy companies that it was common to see want ads seeking such things as an experienced telephone switchman or an experioenced installer or repairman.


The entire area was SxS into the 1930s and mostly in the 1940s.


They developed senders to put in front of the switches to do translations and other functions since the limitations of SxS surpassed the ability of SxS to route calls in the complex and growing area.


London, England, was all step with senders, too, even later than Los Angeles.


Oddly, LA SxS was an early applicator of ANI and call recording. Back
> in the 1940s they had printing tapes automatically tracking short-
> distance dialed toll calls. But I think the ANI they used was
> cumbersome and expensive.

The L.A. area had operator toll dialing in the 1920. The senders made it fairly easy to add other features.


DDD was later added to many all or predominantly step offices, not just in Los Angeles but all over the country. Oklahoma City and Tulsa both got DDD th9s way; I think Dallas, too. It was called Centralized Automatic Message Accounting (CAMA). The Dial 1 for DDD rule fit this application exactly, since on the "1" dial pull the call was trunked directly to the CAMA equipment which handled all subscequent digits.


Wes Leatherock snipped-for-privacy@yahoo.com snipped-for-privacy@aol.com

|Dan Lanciani wrote: |+--------------- || snipped-for-privacy@panix.com (Scott Dorsey) wrote: || |A T-1 circuit transmits 1.54 Mbps, which in a perfect world with zero || |channel noise requires 1.54 MHz bandwidth to transmit. In reality it's || |happy with a bit more bandwidth. || || I would have thought that as the noise approaches zero (and the S/N || ratio approaches infinity) the required bandwidth approaches zero. |+--------------- | |Yes, but... You have to change your encoding to use more distinct signal |levels per Baud, and almost all modems were (and almost all still are) |designed with *fixed* D/A encoding (and AA/D decoding) schemes.



Interesting; I thought V.34 used a variable constellation subset to adjust bits/baud according to line quality.



Anyway, I may have snipped too much. A longer quote:



|Now, back in the days when this stuff was being done, there wasn't any |digital audio transmission. Telephone trunk circuits were created with |frequency division multiplexing of 4 KHz audio channels. I don't recall |the various Telpak channel designations or the exact channel spacing |and guard bands any more, but figure that you can put more than 500 but |no more than 1000 4 KHz channels onto a 4 MHz pipe. I bet a google search |on 'telpak carriers' gets you something a bit better. | |A T-1 circuit transmits 1.54 Mbps, which in a perfect world with zero |channel noise requires 1.54 MHz bandwidth to transmit. In reality it's |happy with a bit more bandwidth.



I assumed we were discussing the bandwidth requirements within a multiplexed carrier, not on a baseband T1 line.



|One notable |exception was the Telebit trailblazer, which chopped the ~3 KHz analog |phone line up into many narrow subcarriers, and could adaptively choose |each sub carrier's modulation among 1, 2, 4, or 6 bits/Baud, depending |on current S/N and IM distortion. It was the exception to the rule.



I still have a small pile of one of the last generation (WorldBlazer) that supported Telebit's PEP. Actually, some of them are T3000s (sent as replacements for T2500s with the one-way data loss) with WorldBlazer firmware but without whatever board change was supposedly required to make PEP reliable. Unfortunately, the T3000 and WorldBlazer suffered from extreme latency in V.32 mode and the ring-no-answer bug that was never (as far as I know) resolved. The last days of Telebit were no fun...



Dan Lanciani ddl@danlan.*com



+--------------- | snipped-for-privacy@rpw3.org (Rob Warnock) wrote: | |Yes, but... You have to change your encoding to use more distinct signal | |levels per Baud, and almost all modems were (and almost all still are) | |designed with *fixed* D/A encoding (and AA/D decoding) schemes. | | Interesting; I thought V.34 used a variable constellation subset to adjust | bits/baud according to line quality. +---------------

I think it does. That's why I said "*almost* all still are"...

+--------------- | Anyway, I may have snipped too much. A longer quote: | | |Now, back in the days when this stuff was being done, there wasn't any | |digital audio transmission. Telephone trunk circuits were created with | |frequency division multiplexing of 4 KHz audio channels. I don't recall | |the various Telpak channel designations or the exact channel spacing | |and guard bands any more, but figure that you can put more than 500 but | |no more than 1000 4 KHz channels onto a 4 MHz pipe. I bet a google search | |on 'telpak carriers' gets you something a bit better. | | | |A T-1 circuit transmits 1.54 Mbps, which in a perfect world with zero | |channel noise requires 1.54 MHz bandwidth to transmit. In reality it's | |happy with a bit more bandwidth. +---------------

NOTA BENE: I didn't write that!!

+--------------- | |One notable | |exception was the Telebit trailblazer, which chopped the ~3 KHz analog | |phone line up into many narrow subcarriers, and could adaptively choose | |each sub carrier's modulation among 1, 2, 4, or 6 bits/Baud, depending | |on current S/N and IM distortion. It was the exception to the rule. | | I still have a small pile of one of the last generation (WorldBlazer) | that supported Telebit's PEP. Actually, some of them are T3000s (sent | as replacements for T2500s with the one-way data loss) with WorldBlazer | firmware but without whatever board change was supposedly required to make | PEP reliable. Unfortunately, the T3000 and WorldBlazer suffered from | extreme latency in V.32 mode and the ring-no-answer bug that was never | (as far as I know) resolved. The last days of Telebit were no fun... +---------------

Maybe, but I continued to happily use my Trailblazer-Plus (T18SA) modems right up until the day I first got DSL.

-Rob

----- Rob Warnock

627 26th Avenue San Mateo, CA 94403 (650)572-2607

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