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Modem and fax tones

Posted on 1998-06-30
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Last Modified: 2013-12-27
I am working witch modem/fax detection.
My problem is that I don't now how I can
 distinguish fax call from modem call.
I wonder if faxes or modems sends tones with
 frequencies that are  unique for modem/fax calls.

Thanks a lot
qtxmiel
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Question by:qtxmiel
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24 Comments
 

Expert Comment

by:vshanks
ID: 1146977
Yes Faxes are sent at a different frequencies then phone calls or modem calls. There is modem software out that you can tell it to only pick up faxes or modem and faxes or voice/fax/modem.
for example winfax pro.
I'm not sure what frequencies they use but the manufactor can tell you.

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Author Comment

by:qtxmiel
ID: 1146978
I will look at winfax pro, but I still don't know if there are some frequencies that
are uniq for modem and fax calls.
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Expert Comment

by:vshanks
ID: 1146979
Good luck in your search.
VS

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Expert Comment

by:alpha786
ID: 1146980
CAN U EXPLAIN WHY U NEED THIS FREQUENCY .
YOU CAN GET EXTERNAL DEVICE WHIC DETECTS FAX AND VOICE TONE .
GOOD LUCK
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Expert Comment

by:aux5
ID: 1146981
i'd love to answer your easy question, but might need to know 1) what kind of modem? and 2) what operating system (win95?)

one thing you can do to check the difference between fax/modem call is this, if you have win95:

control panel, modems, click PROPERTIES, CONNECTION, ADVANCED, put a check in Record a Log File.

If you have Microsoft Fax installed, send a fax to someone with it.
After you send the fax, restart your computer, then connect to the internet.

Disconnect from the internet, then search for a file called MODEMLOG.TXT.

Observe the last two sets of entries, the last one in this text file will be a record of your internet connection.  Check what the init string was for that.  It looks like this:

06-29-1998 04:14:41.76 - Send: ATS7=60S30=0LM1&Q5\N3%C3&K3BN1X3<cr>

Then look at the previous entry, and see if a different init string was sent when you used Microsoft Fax.

Duh, you can also listen to the sounds your modem makes when you do those two things and see if there's a noticeable difference!

Gimme them points or give us more info, amigo!

--eric
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Author Comment

by:qtxmiel
ID: 1146982
More Info:
I do not want to use some software to  distinguish fax call from modem call.
I am working witch voice over IP and are using Dialogic DTI301 board that
can detect diffrent frequencies. Both modem and fax sends 2100 Hz tone
in the beggining of nogation, so I can distinguish modem/fax call from
voice call.
Now I have to now if the call is modem call or fax call so I can choice right codec.
I wonder if faxes or modems sends tones with frequencies that are  unique for
modem/fax calls.
If you answer: Faxes uses X Hz tone. this tone is never used by the modem,
then I give yoy 60 points.
Good Luck
Milosz
Milosz

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Expert Comment

by:joopv
ID: 1146983
There is a very important difference between fax and modem calls:   With a modem call, the called modem starts first with sending tones.  With a fax call, the calling fax starts first with sending tones.

It;s more a timing issue than a signal frequency issue, as far as i know.  When a modem calls you, it will wait with sending tones until you start sending, a fax that calls you will start sending right away.

The official way of finding out this information is by reading the V22, v32, v34 etc. standards documents, and the same for fax (g2, g3 fax standards).

joopv.
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Author Comment

by:qtxmiel
ID: 1146984
If I have anderstand you right, there is no way of nowing if the call is fax or modem call
only by listen to the frequencies.
I have read these recommedations and found that V34 modem do not uses 1800 Hz tones but  faxes do. So you answer is not right. The problem is that V32 modems uses
1800 Hz tone so I can not use these frequency
I have no possibility to see if called or calling modem/fax start sending tones first.
So you solution does not solve my problem.

Tanks for your answer.
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Expert Comment

by:joopv
ID: 1146985
Why don't you read my answer ?

There IS a way : by listening to the incoming call.  If it keeps quit, it is a modem call.  If it starts to scream right away, it is a fax call.

Thats it.

joopv

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Author Comment

by:qtxmiel
ID: 1146986
Hi joopv
Your comment is nor right, I have read your answer.
Example of incomming call from a V34 modem:
The calling modem does not wait until it detects ANSam signal from
answering modem. The calling modem sends a CI (function indikator) signal
before it receive ANSam signal (V8)

Thanks for trying
qtxmiel
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Expert Comment

by:joopv
ID: 1146987
Well, just to be sure i did a small experiment.

I just try'd it myself with my own small (2-port) PABX and a 28k8 noname hayes-compatible modem.

If i dial my other port on the PABX with my modem, and pick up the phone it stays quiet.  If i whistle long and hard in the phone, the modem starts training.

But only if i do that, if i keep my mouth shut or just use voice the calling modem hangs up with "no carrier" message after a timeout.

atdt **1
NO CARRIER

(**1 is the command to dial the other port on the pabx)


Unfortunately i don't have a fax here, but i know from experience that a calling fax starts sending tones right away without waiting for the other party.

Why don't you try it for yourself ?  Dial with a modem to another phone, pick up and listen.  Then do the same with a fax.

joopv


joopv

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Author Comment

by:qtxmiel
ID: 1146988
Hi joopv
This is how it works:
If you ring to a phone from a modem nothing will happend
until the called phone sends answer tone ANS/ANsam/CED (2100 Hz)
If you answer a V34 modem call you can hear CI tone but the modem will
don't do anything until it sense 2100 Hz tone from the answering side
Faxes can work the same way, nothing happent (mayby you can hear CNG tone)
until thay sense 2100 Hz tone, but not all faxes works that way.
Faxex follows T.30 recommendation and there is several ways to set up a call.
My solution must works witch all faxes thats follows the T.30 recommendation.
When you whistle, the modem probobly sensed 2100Hz tone.
When I tried to do your experiment I could hear CI tone from the calling modem
and CNG tone from the calling fax, nothing else happend.

Good Luck
qtxmiel
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Expert Comment

by:joopv
ID: 1146989
I have done some asking around, and it seems to be a problem to make a 100% differentiation between incoming fax or modem calls.

Faxes always start with a FAX CNG tone, which is an intermittent tone.  Modems appearantly sometimes start with a modem CNG tone, although i have never heard one.

Faxes always start with this 300 baud data sequence (bell 212?) but at this point the choice for fax is already made.

Anyway, i think you will have to make some compromise...

Good luck,

joopv

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Author Comment

by:qtxmiel
ID: 1146990
Hi joopv
You have done a very good job, it was a very good effort.
The modems does not use this CNG tone, but the tone
is optional for faxes. So if you don't detect this tone you
can't be sure that the call is not fax.

Thanks
qtxmiel
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Expert Comment

by:shintinsdas87
ID: 1146991
i would just read my owner's manual. it would probably tell you. or you could go to your manufacturer's web page. good luck
0
 
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Expert Comment

by:joopv
ID: 1146992
qtxmiel, what kind of hardware are you using ?

I was under the impression that you are designing your own hardware + software for a fax/modem switch.

Is that correct ?

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Author Comment

by:qtxmiel
ID: 1146993
Hi joopv
Yes, you are rigth. I work witch IP Telephony, and I am using
Dialogic boards to detect modem and fax calls.
(see Comment Thursday, July 09 1998 - 08:11AM)
The solution that I have is not so good, so I hoped that I will get
some more ideas by using Experts Extange.
Probobly I will have to use other hadware to detect modem and fax.

By
qtxmiel

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Expert Comment

by:joopv
ID: 1146994
You're right, sorry for not reading all details.

If you need more ideas : take a look at websites of modem manufacterers.  At Multitech, for example you can download complete AT command set descriptions, also about FAX commands.  Like this one :

+FAA    Auto Answer Mode Parameter
+FAA=0 - Constrains DCE to answer as set by +FCLASS.
+FAA=1 - DCE can answer and automatically determine whether to answer as a facsimile DCE or as a data modem.

Maybe this helps you a little bit further.
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Author Comment

by:qtxmiel
ID: 1146995
Hi joopv
Can I give you some points and still have the question open for other
Experts Exchange users?

You have make a good job.
0
 
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Expert Comment

by:joopv
ID: 1146996
Look what i found at Tandy's website on :

http://support.tandy.com/support_phones/doc19/19565.htm

This is about a home-use fax/data device.  They use the method i described earlier.  If it's good enough for the american citizen, is'nt it good enough for you ?? ;-)

Don't give me any points if your question is not answered, i just like the discussion.  Too bad nobody else with more knowledge is jumping in.


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Author Comment

by:qtxmiel
ID: 1146997
Hi joopv
This AFX-300 Deluxe Automatic Fax/Data Switch listen after fax alert tone. If this tone
is not detected for 20 s, the AFX-300 switch to data mode.
This solution is really bad because fax alert tone is OPTIONAL.
I have check the faxes we have in the lab, only 3 of 5 faxes used this tone.

The other ting:
"When a data modem calls, it makes no sounds at all until your data modem sends
it a signal to beging transmission"
The person who wrote this have not read the V8 recommendation.
The calling modem can send CI tone (optional tone) before reciving the signal
to begin transmission.

I hope that I have understand the text.
By
qtxmiel


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Accepted Solution

by:
Tinkerer earned 70 total points
ID: 1146998
No, no, no... There is no diference between the actuall line carrier frequency of a fax and a modem, THEY ARE THE SAME THING..
It is possible to tell the diference via hardware. but it is NOT based on frequencies, it is based on the way the fax inits answer mode as opposed to the modem...
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Author Comment

by:qtxmiel
ID: 1146999
Hi Tinkerer
I have worked witch modem/fax switch for a while, it's very difficult to built
a modem/fax switch by only listen after frequencies.
Faxes uses 1800 Hz carrier frequencies. The V34 modems do not use
this carrier frequency but V32 modems do.
Insted the V32 modems sends 600 Hz + 3000 Hz dual frequency tone.

So the best way to bulit a modem/fax switch is to use hadware that can
sence V.17, V.27ter V.29, V21 modulation, that is why I accept your answer.

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Expert Comment

by:Tinkerer
ID: 1147000
*LOL* Wow.. Okay, looks like you got it covered..
Sorry I can't give specifics on how to do that..
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