8 ms·

Why don't cell phones have a dialtone?

47 points by dangoldin 14y ago

general_failure 14y ago
afaik, sms is out of band. so it would not have been affected by dialtone.
- cnvogel 14y ago
  Dialing is "out of band" everywhere except analog phones, and dialtones are just the reverse channel giving feedback to the user (just because there's only audio information, a "single band"). The TL;DR of the article probably is: The invention of a separate channel for out-of-band signalling, which the original short-message-services use, was related to the idea to have fully prepared phone-number in a call-setup message to the network.
  - monkeyspaw 14y ago
    Thank you for connecting the SMS to the lack-of-dial tone. I thought it was the most interesting part of the article, but wasn't explained very well. So if I have this correctly: the Push-To-Dial feature necessitated an out of band control mechanism, and this mechanism is what SMS lives on? Do SMS messages still use the out of band? I'm guessing that iMessage, etc., use the data channel (based on the encryption discussion last week). But when I send a text that's a proper SMS, or an SMS from Twilio/etc., does that use this out of band mechanism?
    - rubyrescue 14y ago
      SMS does use the out of band but it was more of an accident of the SS7 protocol. you should read up on SS7 - http://en.wikipedia.org/wiki/Signalling_System_No._7 http://en.wikipedia.org/wiki/Signalling_System_No._7
      - dfox 14y ago
        SMS is more of vestigial debug feature of GSM that was brilliantly commercialized than anything that has to do with SS7. And by the way SMS is out of band on the backhaul network, not on the air interface (and the whole SMS protocol on air interface is horribly complex and inefficient, it essentially involves building data call that passes SS7-like messages, typically one per such "call" in each direction, another funny fact of this technology is that address fields in these messages have larger maximum size (256B) than than actual SMS contents (140B)). But when one wants to take SS7 into this dial tone discussion it is important to note that traditional SS7 call flow (INITIAL ADDRESS/SUBSEQUENT ADDRESS/ADDRESS COMPLETE) is designed for normal incremental dialing and not cell phone style number at once then send style. I'm too lazy to look it up but I believe that GSM's ISUP/DSS1 derived on air signaling protocol is capable of that too (although I've never seen device that allows user to do that). Relatively common user experience problem with VoIP deployments I have seen is that this is effectively impossible with SIP and user has either to explicitly end dialed number with something or wait for some timeout.
        rubyrescue 14y ago
        Thanks for clarifying! It's like i had all the concepts there - out of band and SS7 - but didn't really get the details. This is why I love HN.
D9u 14y ago
I consider a dial-tone to be a waste of network resources.
- dangoldin 14y ago
  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.
philwebster 14y ago
Interesting, I just heard an interview [1] with Marty Cooper (inventor of the cell phone) who is working on a simplified phone for seniors called the Jitterbug. He mentioned that the phone has a dial tone to indicate that the phone has signal. [1] http://hereandnow.wbur.org/2013/04/09/cell-phone-inventor http://hereandnow.wbur.org/2013/04/09/cell-phone-inventor
ultimoo 14y ago
Nice read! On a slightly related note, I wonder why some cell phone service providers are dishonest about a "ringer-tone" (for lack of a better word). The other day in a poor cell reception area I placed my friend's AT&T phone next to mine and dialed her number from my AT&T phone. From my phone we could hear the other phone "ring", however my friend's phone wasn't actually ringing. It then went to voicemail after a few rings. I found it very strange since this is not how cell phones connect in India, for example. I wouldn't have heard the other phone "ring" if it weren't actually ringing on an Indian cell phone service provider.
- CaveTech 14y ago
  Even if I make a call from Skype to my cell phone, I can hear the audible "ring" on Skype long before my actual phone begins to ring.
- dangoldin 14y ago
  It may just be a signal to the caller that something is happening. Otherwise you're left wondering with whether the call went through or not.
- jordan0day 14y ago
  I've noticed this caller-hears-ring-before-actual-ring thing, too (also on AT&T). I always presumed it was a way of giving them (the network) a little longer to make the actual connection, without the caller giving up thinking "it hasn't even begun to ring yet! Something's wrong!"
  - akira2501 14y ago
    That's what this seems to be, I've even noticed that the first ring may even sound a bit different from subsequent rings. I think the first layer ring is the actual call setup being attempted across the cellular network. Once the receiving phone is located and receives the signal that a call is incoming, you begin to hear the second layer ring.
  - caseysoftware 14y ago
    The ring that the caller hears is basically just a recording. And yes, that's it's purpose.. so you know it's doing something before it's actually completed. It's the telecom equivalent of the loading pinwheel.
suyash 14y ago
That is why while making important business decisions it is so critical to think 10-20 years out if not 40-50 even if that makes making the tough choices.
- dangoldin 14y ago
  You should read that book if you haven't already. The old AT&T stressed that type of mindset and had the researchers thinking 50 years and more out while having other groups focus more on development/manufacturing/marketing. I'm not sure many companies can afford to think that way any more given the stock market focus on the short term. I think Google is doing the best job now with the self driving cars/Glass projects.
jlarocco 14y ago
I think I'm missing something because it doesn't seem like a big deal to me. If the first cell phone hadn't done this, what would stop a later phone from doing so? In fact, couldn't any phone buffer the numbers before sending them?
- bskap 14y ago
  People would pick up their shiny new phone, not hear a dial tone, and return it because they think it's broken.
  - jlarocco 14y ago
    I don't think they would. All it would take is a one sentence explanation in the user manual and a blurb on the box claiming it as a new feature.
    - bskap 14y ago
      But that would require them to read the user manual, or the box, or pretty much anything at all. Have you met an average user before?
jere 14y ago
>A caller should dial a number and then push “send.” That way, the mobile caller would be less rushed; Makes sense. I hate landlines for this reason.
dhughes 14y ago
They do in movies, for dramatic effect.
damnusernames 14y ago
does anybody know that this is the reason that Skype doesnt have a dial tone when calling certain lines?
hblieb 14y ago
Here's something else that needs to change. Phones should ring TWICE AS LONG as they do before rolling to voicemail. There are so many times that I miss calls because the time required to detect the ring, locate the phone, get a handle on it and answer the call is MUCH LONGER than it was in the old days! I use Google Voice and an unholy alliance of other devices and services and do not have the ability to solve this problem!

47 points by dangoldin 14y ago

general_failure 14y ago

afaik, sms is out of band. so it would not have been affected by dialtone.

cnvogel 14y ago
Dialing is "out of band" everywhere except analog phones, and dialtones are just the reverse channel giving feedback to the user (just because there's only audio information, a "single band"). The TL;DR of the article probably is: The invention of a separate channel for out-of-band signalling, which the original short-message-services use, was related to the idea to have fully prepared phone-number in a call-setup message to the network.
- monkeyspaw 14y ago
  Thank you for connecting the SMS to the lack-of-dial tone. I thought it was the most interesting part of the article, but wasn't explained very well. So if I have this correctly: the Push-To-Dial feature necessitated an out of band control mechanism, and this mechanism is what SMS lives on? Do SMS messages still use the out of band? I'm guessing that iMessage, etc., use the data channel (based on the encryption discussion last week). But when I send a text that's a proper SMS, or an SMS from Twilio/etc., does that use this out of band mechanism?
  - rubyrescue 14y ago
    SMS does use the out of band but it was more of an accident of the SS7 protocol. you should read up on SS7 - http://en.wikipedia.org/wiki/Signalling_System_No._7 http://en.wikipedia.org/wiki/Signalling_System_No._7
    - dfox 14y ago
      SMS is more of vestigial debug feature of GSM that was brilliantly commercialized than anything that has to do with SS7. And by the way SMS is out of band on the backhaul network, not on the air interface (and the whole SMS protocol on air interface is horribly complex and inefficient, it essentially involves building data call that passes SS7-like messages, typically one per such "call" in each direction, another funny fact of this technology is that address fields in these messages have larger maximum size (256B) than than actual SMS contents (140B)). But when one wants to take SS7 into this dial tone discussion it is important to note that traditional SS7 call flow (INITIAL ADDRESS/SUBSEQUENT ADDRESS/ADDRESS COMPLETE) is designed for normal incremental dialing and not cell phone style number at once then send style. I'm too lazy to look it up but I believe that GSM's ISUP/DSS1 derived on air signaling protocol is capable of that too (although I've never seen device that allows user to do that). Relatively common user experience problem with VoIP deployments I have seen is that this is effectively impossible with SIP and user has either to explicitly end dialed number with something or wait for some timeout.
      - rubyrescue 14y ago
        Thanks for clarifying! It's like i had all the concepts there - out of band and SS7 - but didn't really get the details. This is why I love HN.

D9u 14y ago

I consider a dial-tone to be a waste of network resources.

dangoldin 14y ago
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.

philwebster 14y ago

Interesting, I just heard an interview [1] with Marty Cooper (inventor of the cell phone) who is working on a simplified phone for seniors called the Jitterbug. He mentioned that the phone has a dial tone to indicate that the phone has signal. [1] http://hereandnow.wbur.org/2013/04/09/cell-phone-inventor http://hereandnow.wbur.org/2013/04/09/cell-phone-inventor

ultimoo 14y ago

Nice read! On a slightly related note, I wonder why some cell phone service providers are dishonest about a "ringer-tone" (for lack of a better word). The other day in a poor cell reception area I placed my friend's AT&T phone next to mine and dialed her number from my AT&T phone. From my phone we could hear the other phone "ring", however my friend's phone wasn't actually ringing. It then went to voicemail after a few rings. I found it very strange since this is not how cell phones connect in India, for example. I wouldn't have heard the other phone "ring" if it weren't actually ringing on an Indian cell phone service provider.

CaveTech 14y ago
Even if I make a call from Skype to my cell phone, I can hear the audible "ring" on Skype long before my actual phone begins to ring.
dangoldin 14y ago
It may just be a signal to the caller that something is happening. Otherwise you're left wondering with whether the call went through or not.
jordan0day 14y ago
I've noticed this caller-hears-ring-before-actual-ring thing, too (also on AT&T). I always presumed it was a way of giving them (the network) a little longer to make the actual connection, without the caller giving up thinking "it hasn't even begun to ring yet! Something's wrong!"
- akira2501 14y ago
  That's what this seems to be, I've even noticed that the first ring may even sound a bit different from subsequent rings. I think the first layer ring is the actual call setup being attempted across the cellular network. Once the receiving phone is located and receives the signal that a call is incoming, you begin to hear the second layer ring.
- caseysoftware 14y ago
  The ring that the caller hears is basically just a recording. And yes, that's it's purpose.. so you know it's doing something before it's actually completed. It's the telecom equivalent of the loading pinwheel.

suyash 14y ago

That is why while making important business decisions it is so critical to think 10-20 years out if not 40-50 even if that makes making the tough choices.

dangoldin 14y ago
You should read that book if you haven't already. The old AT&T stressed that type of mindset and had the researchers thinking 50 years and more out while having other groups focus more on development/manufacturing/marketing. I'm not sure many companies can afford to think that way any more given the stock market focus on the short term. I think Google is doing the best job now with the self driving cars/Glass projects.

jlarocco 14y ago

I think I'm missing something because it doesn't seem like a big deal to me. If the first cell phone hadn't done this, what would stop a later phone from doing so? In fact, couldn't any phone buffer the numbers before sending them?

bskap 14y ago
People would pick up their shiny new phone, not hear a dial tone, and return it because they think it's broken.
- jlarocco 14y ago
  I don't think they would. All it would take is a one sentence explanation in the user manual and a blurb on the box claiming it as a new feature.
  - bskap 14y ago
    But that would require them to read the user manual, or the box, or pretty much anything at all. Have you met an average user before?

jere 14y ago

>A caller should dial a number and then push “send.” That way, the mobile caller would be less rushed; Makes sense. I hate landlines for this reason.

dhughes 14y ago

They do in movies, for dramatic effect.

damnusernames 14y ago

does anybody know that this is the reason that Skype doesnt have a dial tone when calling certain lines?

hblieb 14y ago

Here's something else that needs to change. Phones should ring TWICE AS LONG as they do before rolling to voicemail. There are so many times that I miss calls because the time required to detect the ring, locate the phone, get a handle on it and answer the call is MUCH LONGER than it was in the old days! I use Google Voice and an unholy alliance of other devices and services and do not have the ability to solve this problem!