[Eurfyl]

Do mobile phones use DTMF(Dual Tone Multi-Frequency) when dialling another mobile number or is DTMF only for analogue phones i.e. not the digital cellular network? If not then, what do they use?

Thanks

[Ben]

Hi Eurfyl,

I don't believe mobile phones do use DTMF for dialling, no, but it is still used for navigating those annoying 'Press 1 for... Press 2 for...' style menus.

Mobile phones use digital signals, but I don't know any more about how it works than that.

[bsrjl1]

The phone doesn't use DTMF at all - in call setup the dialed number is sent in a signalling message to the MSC, which talks with the PLMN & sets up the call. When you press 1 for Customer Service etc.. the tones are generated in the MSC & added to the call. Due to the compression used, if they were generated by the handset they could be really messed around.

[3g-g]

Hi Eurfyl,

Right, DTMF isn't used for dialling no, I think the handsets still make the tone for the reason Ben mentioned below, some VPS services may need to you enter numbers on the keypad, banking etc.

In the mobile world to dial another number and route calls we use Global Title translation, which is really the SS7 version of IP routing. Translation will examine the number being called and decide how to route the call. The number is sent during the request for resource from the network to initiate your call when you hit the green button.

SS7 is a protocol designed to allow exchanges to talk and exchange info with each other, it's made up of a 7 layer structure, each can be responsible for getting your call to its destination, what ever route that may be. For example messages may be; "here's a call from 07XXXXXXXXX to 07XXXXXXXXX look for it on trunk 050, the called subscriber on trunk 11 is busy, release and play the busy tone, or possibly forward to a voicemail service.

SS7 provides a global standard (apart from the Americans & Japanse) structure for telephony network signaling, messaging, interfacing, and network maintenance. It'll deal with establishment of a call, exchanging user information, call routing, different billing structures, and supports Intelligent network services.

SS7, Global title translation and analysis that's what you need to learn :)

[3g-g]

Ahh, there you go, DTMF generated in the MSC... I thought the handsets could still make the tones. :)

[Ben]

My Z1010 didn't work with 'Press 1' etc services, like Orange CS. Hence why I assumed it was a handset thing? It was a handset fault.

I suppose the handset could have simply been sending nothing at all, so there was nothing for the MSC to work with...

[Eurfyl]

So if for example mobile A rings mobile B and B answers, can mobile A send an AT command to mobile B if mobile A presses one of the keys on the mobile itself?

If an AT command is sent then will the AT command show which button was pressed.

[bsrjl1]

The mobile only has a signalling connection to the MSC, so there is no direct communication between A & B. I don't understand what you mean by AT commands?

[Ben]

I wouldn't have thought AT commands feature - aren't they used by computers when communicating with analogue telephone line modems (ie Dialup)?

In any case, I would guess the answer is no.

[Eurfyl]

Yes I thought ATcommands sets features on modems. I take it that there is a e.g. gsm modem in a mobile phone and that when you dial a number and then press the green hanset key then you send and ATD to the modem which is an AT command to tell the modem to dial that number.......so I was just wondering e.g. if I ring your mobile and you answer and then during a chat I press a key on my mobile then you hear a tone depending on which key I press, but how does that tone get there? Just wondering if my phone sends an ATcommand to your phone......

[bsrjl1]

No there's no modem in a phone, the MSC does it. You've really got to realise that a mobile phone isn't just a PSTN phone that's not plugged into anything! And no, before you ask, SMS don't get delivered to the phone via DTMF either! Look up SS7 signaling in google & have a good read.

As far as the content of a data call, you send the raw data to the MSC, and it has an Interworking Function that either connects to ISDN, or modulates/demodulates the data call into 'normal' modem sounds. HSCSD will get you 28.8kbps, so it's slow & that's why GPRS is more popular.

The DTMF tone is generated by the MSC, as I said before.

[3g-g]

Yes I thought ATcommands sets features on modems. I take it that there is a e.g. gsm modem in a mobile phone and that when you dial a number and then press the green hanset key then you send and ATD to the modem which is an AT command to tell the modem to dial that number.......so I was just wondering e.g. if I ring your mobile and you answer and then during a chat I press a key on my mobile then you hear a tone depending on which key I press, but how does that tone get there? Just wondering if my phone sends an ATcommand to your phone......

Eurfyl,

There's a bit of knowledge within the forum that can probably answer most things you post on here, perhaps if you gave us an idea into the background of your questioning we could give you a hand, or at least point you in the right direction?

Are you trying to set up some sort of remote telemetry or monitoring? That's what I get from the questions you've asked so far... is it a project or University? or are you just genuinely interested!?

Don't be shy now!