Author Topic: How does digit absorbing work?  (Read 585 times)

bellsystem

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How does digit absorbing work?
« on: July 23, 2017, 07:09:21 PM »
For some reason, digit absorbing in SxS seems intriguing. I've been trying to find out how it works, but I can't find any resources that really detail how digit absorbing selectors work.

For example, from: In order to accommodate inbound DDD, it was essential that every number have a 7-digit format. But SxS switches couldn't accommodate 7-digit dialing, so telcos faked 7-digit numbers by prepending dummy digits. Local calls continued to be dialable with only four or five digits; however, if a local caller actually dialed all seven digits, the prepended digits were absorbed by "absorbing selectors" -- i.e. ignored.

Here is an example of digit absorbing in action: https://youtu.be/_VO7MWFI9SU?t=661 (right at 12 minutes). Phil explains at 12 minutes that the digit 7 will continue to be absorbed.

And a great technical explanation is available here: http://www.telephonetribute.com/switches_survey_chapter_4.html

From this, I've grasped that there are special selectors that will absorb a specific digit. In Phil's case, his exchange was 377 and to absorb the 7s, the fourth(?) selector is "programmed" to absorb the digit 7 (once? twice? forever?). The rest still seems pretty ambiguous though. For instance, what is the mechanism that unlocks the selector? Can anyone offer an explanation, or point me to some resources (i.e. BSPs) that offer one? Thanks!
« Last Edit: July 23, 2017, 07:15:52 PM by bellsystem »

Alex G. Bell

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Re: How does digit absorbing work?
« Reply #1 on: July 23, 2017, 07:32:25 PM »
Look in the TCI library for Automatic Electric Training Bulletin 808, 945-808 or 948-808 titled "Selectors".  It explains digit absorbing selectors from A to Z.


bellsystem

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Re: How does digit absorbing work?
« Reply #3 on: July 24, 2017, 12:02:52 PM »
Well, I've spent the last hour and a half downloading Automatic Electric PDFs. I have 320 more MB now that I didn't wake up with. I found 945-800 and 945-801. Some of the other 945-series bulletins just had the 8xx number, and I renamed these so they all had standardized file names. I'm currently missing 803, 805, 808, 809, 811, 812, 814, 816, 818, 819, and 821.

Yes, I've spent a significant amount of time scouring the Internet for the others.

Are these available somewhere, or lost to time? 808, "Selectors", is one of the bulletins recommended to me, and also one of the ones I currently do not have. And typing in "automatic electric bulletin 945-808 selectors" does not bring it up.

Offline AE_Collector

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Re: How does digit absorbing work?
« Reply #4 on: July 24, 2017, 01:35:02 PM »
In Phil's case, his exchange was 377 and to absorb the 7s, the fourth(?) selector is "programmed" to absorb the digit 7 (once? twice? forever?).

There were lots of options.
Absorb once and then cut in on the next digit even if it were the previously absorbed digit.
Absorb repeatedly.
Other scenarios such as absorb twice and then cut in may have been possible.
At least some of the absorbing was triggered by what we called a "comb" on the top of the selector shaft that had 10 "teeth" on each side of it representing the ten levels that could be dialled. A contact set on each side of the comb would be operated if a tooth were missing triggering either absorb once or absorb repeatedly depending which side of the comb triggered it (I believe...it's been a long time). Early combs were metal and a tooth could be bent out of the way thus it could be returned to normal in the future but later combs were plastic (white plastic in my experience) where a tooth was broken out so it wasn't reversible in the future but would just be replaced.

Terry

Alex G. Bell

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Re: How does digit absorbing work?
« Reply #5 on: July 25, 2017, 06:36:02 AM »
Well, I've spent the last hour and a half downloading Automatic Electric PDFs. I have 320 more MB now that I didn't wake up with. I found 945-800 and 945-801. Some of the other 945-series bulletins just had the 8xx number, and I renamed these so they all had standardized file names. I'm currently missing 803, 805, 808, 809, 811, 812, 814, 816, 818, 819, and 821.

Yes, I've spent a significant amount of time scouring the Internet for the others.

Are these available somewhere, or lost to time? 808, "Selectors", is one of the bulletins recommended to me, and also one of the ones I currently do not have. And typing in "automatic electric bulletin 945-808 selectors" does not bring it up.
That's very curious.  I went to the TCI library basic search, searched for "808" and found two instances among a total of 5 matches, 3 of which were irrelevant.  I was pretty sure it was there before checking and now that I have checked I've found that my recollection was correct:

5. AE Bulletin 808 Mar58 Selector
    (Download:Bruce Crawford Library/Automatic Electric/Bulletins)
    Contributed by Alan David and John Novack.
    Created on 05 May 2011
6. AE-Bulletin-945-808 Selector
    (Download:Bruce Crawford Library/Automatic Electric/Bulletins)
    Created on 05 February 2011

I also found them less directly by browsing but that probably requires some familiarity with the organization of the library whereas basic search is... well... basic.

Accordingly I'm going to leave it to you find the remaining missing ones based on my recollection (probably correct) that most or all are there and can be found with a few seconds effort.

Offline TelePlay

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Re: How does digit absorbing work?
« Reply #6 on: July 25, 2017, 01:22:40 PM »
That's very curious.  I went to the TCI library basic search, searched for "808" and found two instances among a total of 5 matches, 3 of which were irrelevant.  I was pretty sure it was there before checking and now that I have checked I've found that my recollection was correct:

IIRC, you have to be a member of TCI to get access to the BSP library and other library documents.

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            John . . .

              

Alex G. Bell

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Re: How does digit absorbing work?
« Reply #7 on: July 25, 2017, 01:29:41 PM »
IIRC, you have to be a member of TCI to get access to the BSP library and other library documents.

     http://www.telephonecollectors.info/
You remember wrong.  Anyone in the world can access TCI library docs.  Only a very few catalogs which are not in the TCI library but in a members-only area of the webpage are limited to dues paying members.  They are restricted this way at the stipulation of the person who invested many hours scanning them and wanted them there to encourage support of the TCI's activities.

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Re: How does digit absorbing work?
« Reply #8 on: July 25, 2017, 01:35:35 PM »
You remember wrong.

Alex, thanks. Being a member with full access to everything, I new of the members area being just that but you are right, the docs are available to anyone who really wants to spend a little time searching for what they want.
            John . . .

              

Alex G. Bell

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Re: How does digit absorbing work?
« Reply #9 on: July 25, 2017, 01:38:20 PM »
Alex, thanks. Being a member with full access to everything, I new of the members area being just that but you are right, the docs are available to anyone who really wants to spend a little time searching for what they want.
You're welcome.  The TCI Library is the TCI's gift to posterity.  Making it public was a very conscious choice by many people involved and committed to the group and to preserving and perpetuating the vast body of knowledge about this technology.