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Strowger - Hah! | 439 comments | Create New Account
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Strowger - Hah!
Authored by: bprice on Saturday, May 19 2012 @ 10:57 PM EDT
Could you replace it with the calculator buttons? Does the relationship of symbol to actual numeric value harm the dissertation?
Yes, but calculator buttons would lead to a much less clear differentiation, in my opinion.

The Strowger-switch example can be taken to much greater detail:

In the original direct-dial telephone, the digit-symbols and letter-symbols of the "telephone number" are individually translated into a unary code, represented by a pulse train. This encoding – visual symbol to electrical symbol – is what drives the strowger switch exchange. This is a trivial symbol mapping, requiring no lookup. The mapping is built into the dial mechanism, completely.

It's possible to bypass the dial and generate the pulse train directly, as I learned as a kid. That doesn't change things. In current practice, in any exchange that's responsive to pulse train encoding, each digit's encoding is mapped, directly, to DTMF (or maybe an MF) or to the telco variant of BCD (where '0' is coded as 0xA, decimal 10) for further use.

The point is that the older technologies used the encoding of the visual symbol as a direct mapping to the network hardware, which is exactly analogous to memory addressing and index fiddling. The symbol is trivially modified by the technology into something directly useful. This is the kind of usage that the CS term of art 'direct' encompasses, and which is absent in the 'symbolic' term of art.

In later network technologies, staring with IIRC, panel switching, the mapping from symbol to physical is less trivial: I don't know panel-switch tech well enough to make a firm statement. The current technologies, however, definitely treat the 'telephone number' string ('directory number') as a symbol used by a lookup mapping to the physical.

IIRC, the ESS-1 used a table made from ferrite ROM for the lookup: any change in the mapping required a change in the table's wiring. But it was still a direct mapping, of the trivial kind. That's not the current technology. The advent of 'number portability' made it necessary to do a database lookup of the directory number in order to determine anything about the destination RJ-11 or cell-phone ESN. That's a nontrivial lookup, as the front end to more processing — thus, the 'telephone number' is now properly treated, in CS terms of art, as a symbol.

---
--Bill. NAL: question the answers, especially mine.

[ Reply to This | Parent | # ]

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