[Pix]

don’t you ever sleep ?? 🙂

i’ll check if there is any history on such problem.
on your side, could you see exactly how are transmitted these “tones” ? are they sent over TCH or FACCH or SDCCH ?
you would need to find the message flow, and therefore get in touch with the company that builds the modem (??)

I suspect they are using “Supplementary Services” ?

>> Pan “Mr 3GPP”, what do you think ?

you could check the MC02xx associated with supp services.

[Ivann]

Dear Pix,
:)))
thanks a million for your preciuos help. I’m checking all points you recommended right now.

[Pan]

Dear, Pix and Ivann!
Obviously these modems use DTMF tones. they are realized by means of Start DTMF, Stop DTMF messages on signalling channel (FACCH on RF-interface) (during conversation) from MS to MSC and inband dual tone multifrequency (DTMF) signalling from MSC to PSTN (any tones and speech recognition equipment). Tandem Free Operation also uses inband signalling for codec negotiation hence it is possible some collisions. But TFO must be not used in PSTN direction.
B.R.

[pix]

thx pan !

the only reason why the TFO would interfer is if the server itself is communicating with a modem.

in this case, we would have ms-ms calls (or modem-modem).

the thing i don’t understand is why the TFO would impact the FACCH. They are not carried over speech frames, they probably go through the RSL on Abis and N7 ts on the A interface, don’t they ?

Before “Ivann” can confirm, don’t you think it is possible that both modems are sending tones over speech frames ?

i forgot to check “TFO faults database” at work, i’ll try to do it tomorrow.

[Pan]

Hello, Pix! As I understand TFO is protocol between two transcoders, but not between trau and MS. My knowledges in this area are very vague and I need learning:). Moreover we are saying about TFO as Tandem Free Operation (inband signalling), but not about TFO as Transcoder Free Operation (outband signalling), isn’t it? Collision between trau signalling or even radio-encoded speech on PCM and DTMF may occur when MSC interworking equipment generates DTMF (from mobile) simultanuously with TRAU signalling. There is no standard way to deliver DTMF from network to mobile and the gsm codec in trau heavily distorts DTMF tones when they come from network in speech channel.

[Pix]

quickly, there is TFO TC-MS and “TrFO” TC-core.

i don’t know much about TrFO, but TFO is inband, and between MS and TC.

thx for the inputs about DTMF 🙂

[Pix]

That’s a msg from Ivann:

Hello,

You are right : they use DTMF tones. And yes, as their expert said, that server isn’t an ordinary one (PSTN as usual) “it’s also a modem connected to a terminal”. (The weirdest solution I’ve ever seen…)

It’s true, we have something like MS-to-MS schema. So we have one question (as I understand): on which channel are modems sending these tones (FACCH or ordinary speech frames)?
In some days I’ll be there and I’ll see this “invention” with my own eyes.

[Pix]

Ivann,

My suggestion, for quick solving : open a ticket with your RTAC ! I see some history about DTMF and TFO, they will help you out better than I.

[Pan]

Hello, Pix! TFO operation is determined in 03.53. It is used inband codec negotiation between local and remote trau right after call setup. The local trau sends TFO_REQ message by stealing one bit out of 16. “This allows to have the least possible degradation of the PCM, since the TFO_REQ message is sent even in cases where TFO will not be possible e.g. MS to PSTN call.”.
If there is no TFO_ACK after several TFO_REQ then negotiation is stopped. I.e. TFO_REQ is sent on user channel on initial phase of call.
Interworking equipment in MSC also generates tones on user channel in PSTN direction. It may be DTMF tones or V-series modems procedures (e.g. V.34 etc.) depending on equipment type.
If server in PSTN generates DTMF tones then they are delivered to MS on user channel all the way (there is no Start-Stop DTMF messages in Netork-MS direction) with distortion by GSM codec in trau. It is MS responsibility to recognize such distorted tones. In this case it is really a weird solution.

[Pix]

Pan,

Have you read the post from Ivann (that i have forwarded on her behalf) : the server is communicating with a modem too.

So it is like a MS-MS call. What happens when a MS sends a DTMF to another MS…? Why would there even be TFO ? Are the three requests polluting the DTMF tones ?

I found some Alcatel-Lucent fault reports about TFO and DTMF, but i don’t know if it’s related to this issue exactly.

[Pan]

Yes, Pix, I have read the post from Ivann:)
When I am saying ‘modem’ I am imaging device supporting data transfer over the telephone network according ITU-T V-series recomendations. When I am saying ‘DTMF’ I am imaging a device on user side that supports DTMF-alphabet (8 frequencies from voice band by means of which the figures from 0 to 10 and (#,*) symbols are encoded)….

[Pan]

…You say: “So it is like a MS-MS call”. Then I have a question: “Is ter*minating party located on PLMN or PSTN?” Originating party is located in PLMN as Ivann said.
When one MS sends DTMF-tones to remote side in conversational state it sends Start DTMF on FACCH and then (after period of time approximately 40-70 ms) it sends Stop DTMF on FACCH. These nessages is transfered on the signalling channels (not traffic) from MS to MSC. Then MSC generates DTMF tones (according to number of frequency in Start DTMF commands) to remote side. These tones is transfered in voice band on traffic channel (no matter PLMN or PSTN are remote party).
If remote party is in PSTN then collissions (if any) may occur only in MS to PSTN direction. There is no trau in PSTN, hence the TFO signalling in backward direction is not present.
The TFO_Req may be sent up to 35 times if no TFO_Ack from remote side. One TFO_Req – 50-70 bits and is sent during about 100-140 ms (see 08.62).
But as you may see from my questions I have no clear visualization of picture (Is it really DTMF-modems?, modems location? etc.).
B.R.

[Pix]

Pan,

I’m still to keep up with you here 🙂 Could you explain the start DTMF / stop DTMF again ? Let see if I understood correctly :

in the “start DTMF” msg, there is a list of digits, which are decoded by MSC as being tones ? And the MSC sends these tones to the remote party ?

What is the purpose of stop DTMF ?

The remote party (according to Ivann) is a GSM Modem. So those tones are sent from MSC to this modem over the TCH channel, like a typical speech frame ?

Sorry to be a little dumb here, it’s not clear to me how DTMF works 🙂

[Pan]

Hello, Pix! Our activities is not stoped even in the weekend:)
Start DTMF message is initiated by depression of a key button in mobile phone in speech call. Stop DTMF message is initiated by release key button in the phone. Start DTMF message contains the digit value (0-9,*-A,#-B). A digit value corresponds a certain combination of frequency pair:
for example, 1= 697Hz+1209Hz,#=941Hz+1477Hz etc. The digit value from Start DTMF message is converted in MSC to dual frequency signal and sent on traffic channel. And so on. Also Start-Stop message may be transfered automatically within timing restriction for DTMF (70 ms – tone, 65 ms – pause). See also 23.014 about DTMF in PLMN.
B.R.

[Pix]

ok ! now it’s clear – thank you –

and i will understand what are those ALU fault reports about TFO and the “Stop DTMF” message. I saw something, but I couldn’t understand at that time…

… until i talk to pan 🙂

No week-end for the nerds !!!!!!!!!!

[Author]

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