Troubleshoot DTMF problems on your PBX

DTMF problems:Some of the biggest problems of companies that use pulse dialing PBXs is the delay in calls, unsatisfied or unattended customers, lost sales… Do you know what DTMF is, and what are the advantages of installing it in your virtual PBX? Don’t stop reading this article, 🥇 we explain it all!

Before getting into the subject about the possible pbx problems, we must explain what is DTMF in the virtual PBX of telephony so that everyone understands it.

When we talk about DTMF or Dual-Tone Multi-Frequency, we refer to the signal that is emitted to the company by tone (voice) dialing. In other words, it is the tone transfer emitted when dialing on the telephone during a conversation.

As a rule, it is used to pass a certain call to an extension set in the voice menu of the PBX, because sometimes it does not detect the dialing of the number on the phone.

For example, dial 1 for information, dial 2 for collection, …. These tones are commonly used by telephone operators, medical centers, banking entities, …

The main benefit that companies obtain with DTMF is that the signals emitted by tone are much faster than those emitted by pulse (pressing the key). This is because pulse dialing requires sending multiple signals for each number, while tone dialing only needs to send one signal.

If we compare pulse dialing and tone dialing, we find that DTMF:

  • Reduces dialing errors
  • It is faster, because you don’t have to wait so long for the PBX to detect the interruption, depending on the number dialed.

One of the main concerns of companies that do not have the DTMF tone service in their virtual PBX is the loss of patience on the part of the customer in the case of service companies (medical centers, …) or the loss of a sale if it is a business (telephone companies).


cliente enfadado


What are the possible DTMF problems of a PBX?

A well configured PBX with its DTMFs set according to the needs of the company should not give any pbx problems. In the case that something is not well configured, we can find 2 problems:

1- If it happens to all callers, whatever their operator and telephone terminal: the problem is that the PBX is not well configured.

In this case, you should contact your provider and make sure that the DTMF tones are not configured as in-band audio, but encoded according to RFC2833 in RTP or as INFO messages in SIP.

To avoid these problems, Gesditel configures the interactive menus of its clients (or auto attendants) to react even if no DTMF tones are received. This ensures that the call is not lost.

For the transmission of tone dialing signals, we have 3 methods available:

  • In-band: the tones are sent in an uncompressed voice stream. It is very demanding on the quality of the Internet.
  • RFC2833: tones are transmitted separately from the speech stream. This method works with any audio codec and does not depend on the quality of the connection.
  • SIP INFO: DTMF tones are sent in the SIP INFO message, dialed tones can be viewed inside the SIP packet in SDP.

2- If it only happens to iPhone users, there is a “bug” (software bug or defect) that prevents some iPhones from sending DTMF tones correctly. To fix it just follow a few simple steps:


1) Turn on the home wifi.
2) Connect your phone to the wifi
3) Move to a strong wifi zone
Enter Phone.
Tap Keypad if necessary.
Type ## CLEAR # (## 25327 #).
Hit Call.
Tap Accept at the message Reset subscriber settings.
Allow the radio to reboot.


troubleshoot dtmf


What are the characteristics of the DTMF auto-tone?

DTMF auto tone, primarily, is characterized by the emission of two tones of different frequency when performing voice dialing. One tone is from the column and the other from the row to which the key corresponds, thus establishing the number you dialed.

The level of the signal emitted by the tone dialing system has frequencies that in the intermodulation products (they are generated by the nonlinearities of the output amplifier, transmitter and passive devices) admissible are:

  1. Each transmitted frequency may vary ± 1.8 % of the nominal frequency.
  2. Distortion products, produced by intermodulation or harmonic generation, must have a level 20 dB below those of the fundamental frequencies.
  3. The sound emitted when a key is pressed is the sum of a high tone (the tones of the keyboard columns) with a low tone.

Currently, tone dialing equipment has integrated circuits that are responsible for generating the tones while consuming little current from the mains.




If you are interested in the management of virtual PBXs, you may be interested in reading about how you can improve your PBX internally with the use of codes.

If, on the other hand, you are interested in improving your PBX to avoid losing customers and/or sales, do not hesitate to contact us to find out more about our call center software. We will be happy to assist you and help you without any obligation.

(Votos: 1542 )
Por: Nati CaballeroPublicado el: 12 de mayo de 2022