![]() RFC4733 (and previously RFC2833) specifically defines the payload formats for handling the packet structure for DTMF and other tones, signals and telephony events when transported across IP Networks. The adoption of International Telecommunication Union (ITU) Request for Comments (RFCs) ensures consistency of approach between communications providers and helps to ensure that the telecommunications industry interconnects on common terms and specifications so as to avoid issues with incompatibility. So what can be done to ensure DTMF is reliable? In other words, the frequencies that identify the digits are also compressed and the effect is that those digits are no longer recognisable by the time they reach the IVR. ![]() With DTMF, however, if it is also transmitted within the speech path then it will also be subject to the actions of the codec. G729, G723) means that the frequencies that make up your conversation are compressed in a way that reduces (usually imperceptibly) the quality of your speech. ![]() The actions of applying lower quality codecs (e.g. So how does it work today?įast forward to today, however, and many networks now employ internet-based technologies and IP transit connections and rely on packet-based switching and transmission, and in certain situations where capacity is costly or limited, employ compression/decompression coding and decoding (codec) algorithms that reduce voice packets and therefore the bandwidth required for each telephone call. DTMF was also considered in this process, and hence not affected during the coding and decoding process due to the high quality (8 kHz) sampling rate used. When the industry moved to digital call transmission, the analogue audio signals needed “digitising” and were sampled in a way that transformed (coded) your voice call into a series of digital signals (8 bits in length) that were transmitted to a decoder at the remote end for reconstituting into an audio signal (your voice). ![]() When DTMF was first developed in the 1960s, all of its frequencies were easily transported across the public switched telephone network (PSTN) together with speech, as the analogue nature of the connections meant that frequencies were not compressed or subject to any losses, other than where physical distance required amplification of the signal.
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