RFC 4967, "Dial String Parameter for the Session Initiation Protocol Uniform Resource Identifier", July 2007Source of RFC: IETF - NON WORKING GROUP
Area Assignment: rai
See Also: RFC 4967 w/ inline errata
Errata ID: 3723
Publication Format(s) : TEXT
Reported By: Gagandeep Singh
Date Reported: 2013-09-12
Verifier Name: Gonzalo Camarillo
Date Verified: 2013-11-14
Section 3 says:
Thus, the digit 2 is the first row, second column, and consists of 770Hz and 1209Hz frequencies mixed together.
It should say:
Thus, the digit 2 is the first row, second column, and consists of 697Hz and 1336Hz frequencies mixed together.
As per the specification, DTMF is a 4 x 4 matrix with four row frequencies (697, 770, 852, 941 Hz) and four column frequencies (1209, 1336, 1477, 1633 Hz).
Thus correct matrix for digit 2 should be (697Hz, 1336Hz)