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Definitely. The book didn't really cover the "why" around why landlines had a dialtone but my suspicion is that the systems failed frequently enough that they w

Definitely. The book didn't really cover the "why" around why landlines had a dialtone but my suspicion is that the systems failed frequently enough that they wanted to signal to the user that the phone was ready for use. I may be entirely wrong.

raganwald 14y ago
I'm not sure, but at one time there were also a lot of party lines. A dial tone was a way of signalling that you had the line to yourself and you weren't picking up during a lull in someone else's conversation. Today we have the signal bars to show you status. Back then, a light would have added expense and complexity to the phones of the day.
greenyoda 14y ago
A phone switch can only accept a finite number of connections at a time, and a dial tone indicates that you have succeeded in connecting with the switch. If 100% of the capacity of the switch is currently in use (as could happen during a natural disaster), then you won't get a dial tone. We tend to take the dial tone for granted because the phone system almost always has enough capacity to let us make a call without waiting.
- dfox 14y ago
  In case of touch tone dialing there is another aspect: classic analog or hybrid (analog call path with computer control) switch has relatively small amount of touch tone decoders (2 for 50 lines and ~10 simultaneous calls being relatively common ratio for PBXes), mechanical pulse dialing-only switches are similarly limited by number of step by step switches. Thus dialtone indicates that: (1) line is reasonably usable, (2) switch has at least theoreticaly resources to connect some call (not necessarily any) and (3) switch actually has resources to decode number you are going to dial. I have seen hybrid PBXes where dial tone is generated by same part of circutiry that decodes DTMF.
darkarmani 14y ago
You are right. There are two things going on here: 1. They added background noise to the actual calls to let people know they other end wasn't disconnected. The clarity got too good and people couldn't tell they were still connected. Fun fact: PCM - g.711 - is 64-kbits - hence max modem speed. 2. Dialing used to use in-band signalling and the tone lets you know you can dial (phreakers could use this to get free calls). When the dial tone ends, you know that your call is going through.
- akira2501 14y ago
  The dial tone actually ends after the first digit is dialed. However, this is a significant digit, especially for older equipment. If you pressed 0, you would get the operator immediately. No phone numbers could begin with zero. If you pressed 1, you would be connected to a long distance trunk and an area code would then be expected. No local prefixes could begin with 1. If you pressed any other number it was a local call. Also, on analog networks, maximum modem speed was 56kbps. 64k was the theoretical maximum, but the FCC placed limits on the amount of power you could have in certain frequency bands on the line -- hence 56k was the maximum speed. On a purely digital network, like ISDN, you could receive 64kbps on each channel.

raganwald 14y ago

I'm not sure, but at one time there were also a lot of party lines. A dial tone was a way of signalling that you had the line to yourself and you weren't picking up during a lull in someone else's conversation. Today we have the signal bars to show you status. Back then, a light would have added expense and complexity to the phones of the day.

greenyoda 14y ago

A phone switch can only accept a finite number of connections at a time, and a dial tone indicates that you have succeeded in connecting with the switch. If 100% of the capacity of the switch is currently in use (as could happen during a natural disaster), then you won't get a dial tone. We tend to take the dial tone for granted because the phone system almost always has enough capacity to let us make a call without waiting.

dfox 14y ago
In case of touch tone dialing there is another aspect: classic analog or hybrid (analog call path with computer control) switch has relatively small amount of touch tone decoders (2 for 50 lines and ~10 simultaneous calls being relatively common ratio for PBXes), mechanical pulse dialing-only switches are similarly limited by number of step by step switches. Thus dialtone indicates that: (1) line is reasonably usable, (2) switch has at least theoreticaly resources to connect some call (not necessarily any) and (3) switch actually has resources to decode number you are going to dial. I have seen hybrid PBXes where dial tone is generated by same part of circutiry that decodes DTMF.

darkarmani 14y ago

You are right. There are two things going on here: 1. They added background noise to the actual calls to let people know they other end wasn't disconnected. The clarity got too good and people couldn't tell they were still connected. Fun fact: PCM - g.711 - is 64-kbits - hence max modem speed. 2. Dialing used to use in-band signalling and the tone lets you know you can dial (phreakers could use this to get free calls). When the dial tone ends, you know that your call is going through.

akira2501 14y ago
The dial tone actually ends after the first digit is dialed. However, this is a significant digit, especially for older equipment. If you pressed 0, you would get the operator immediately. No phone numbers could begin with zero. If you pressed 1, you would be connected to a long distance trunk and an area code would then be expected. No local prefixes could begin with 1. If you pressed any other number it was a local call. Also, on analog networks, maximum modem speed was 56kbps. 64k was the theoretical maximum, but the FCC placed limits on the amount of power you could have in certain frequency bands on the line -- hence 56k was the maximum speed. On a purely digital network, like ISDN, you could receive 64kbps on each channel.