Section: 5.5.7.5 Sequencing of subsequent start DTMF requests by the mobile station
Content: If the network is generating DTMF tones it shall ensure that the minimum length of tone and the minimum gap between two subsequent tones (according to ETSI ES 201 235-2 [12a]) is achieved. NOTE 1: In ETSI ES 201 235-2 [12a] the minimum duration of a DTMF tone is 65ms. NOTE 2: In ETSI ES 201 235-2 [12a] the minimum gap between DTMF tones is 65ms. There is no defined maximum length to the tone, which will normally cease when a STOP DTMF message is received from the MS. However, the operator may choose to put a pre-defined time limit on the duration of tones sent. The appropriate sequencing of DTMF control messages is shown in figures 5.8 and 5.9. NOTE 3: The network may implement the time limit option where the DTMF tone duration is controlled by the network irrespective of the receipt of a STOP DTMF message from the mobile station. Figure 5.8/3GPP TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ]  Single DTMF transmission Figure 5.9/3GPP TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ]  Multiple DTMF transmission