Transmit DTMF Based on RFC2833

Alaul Diamond Medal

(1)
7 years 10 months ago View: 5395 Reply: 25

1F
View The Author

The UMG8900 supports the transmission and detection of DTMF signals through RFC2833. In V oIP applications, low-rate codecs are often used to obtain efficient bandwidth usage. The current low-rate voice codes such as G .729 and AMR, however , are designed for voice signals. The qualities of monophonic signals such as DTMF and dial tone signals are subject to degradation after the low-rate voice codec, which disables the peer end to correctly receive the monophonic signals and adversely affects the services that are linked to the monophonic signals. In other words, the IP packets in voice encoding format are not suitable for transmitting the monophonic signals.The IETF formulates the RFC2833 standard to effectively transmit the monophonic signals with high bandwidth usage. RFC2833 provides a solution that enables in band transmission of monophonic signalsover RTP . RFC2833 supports the inband transmission of signals of multiple tones including DTMF tones, fax tones, data modem tones, telephony tones, and trunk tones.

RFC2833 canbe implemented in two modes: named signal mode and tone representation mode. When the RFC2833 transmission mode is enabled, if DTMF signals are detected in the PCM code stream at the transmitting end, the UMG8900 sends the appropriate RFC2833 packets to thepeer endbased on the level and length of DTMF numbers. The UMG8900 supportsboth the named signal mode and tone representation mode. Each DTMF signal is composed of twooverlapped sine waves of dif ferent frequencies. For instance, 697 Hz and1209 Hz are used for the number1. If the named signal mode is used, the currently transmitted DTMF number is identified as1 in the RFC2833 packet. If the tone representation mode is used, the currently transmitted DTMFnumber is not specified in the RFC2833 packet; instead, the frequencies697 Hz and1209 Hz that are contained in the monophonic tone signal are specified. Based on the received frequency information, the peer end determines that the DTMF number is 1, and then generates the PCM signal.

The RFC2833 packets canbe always received. Therefore, the UMG8900 generates the PCM data that corresponds to the DTMF number upon the receipt of the RFC2833 packets.

This feature is applicable to the VMSC, GMSC, and TMSC.

Comment| Reply

Favorite (0) | Like 2 |Report

zsiddique Platinum
7 years 10 months ago

2F
View The Author

What is the benefit of DTMF?

Comment| Reply

|Report