Celebrate World Telecommunications Day 2017

The aim of World Telecommunications Day is to highlight the importance of communication and how information travels across the world.

The day is closely  connected with the International Telegraph Union (ITU), the committee formed in 1865 to handle the emerging technologies.

We’re celebrating Dual-Tone Multi-Frequency signalling (DTMF). This is in-band signal alongside the normal voice data, between equipment and other devices and usually at the exchange. DTMF was first developed in the Bell System.

Data Structure Diagram illustrating DTMF
DSD showing DTMF signalling tone

Data Structure Diagram (DSD)

DSDs are a graphical alternative to the composition specifications in data definitions. In our model of the DTMF, the signal is shown comprising of the Low Tone and the High Tone. These are  made up of the individual optional low and high tone components.

If you want a teaser for World Telecommunications Day 2017, why is the 1633Hz frequency not shown?

Answer below:





The 1633 tone was developed for early data access and would have had keys A,B,C,D, in a column alongside 3, 6, 9 and #. The phone pictured does not have these keys. These tones are used in radio and inter exchange equipment only.