| 摘要 |
PCT No. PCT/FI96/00181 Sec. 371 Date Sep. 19, 1997 Sec. 102(e) Date Sep. 19, 1997 PCT Filed Apr. 2, 1996 PCT Pub. No. WO96/32817 PCT Pub. Date Oct. 17, 1996According to the invention, when detecting the same DTMF signal at the transmitting end, successive DTMF frames relating to this signal are established. These frames are modified SID frames, and individual linking information (Order, Start, Duration) is added to each frame in addition to DTMF signal frequence pair information. This linking information indicates the duration of the DTMF signal from the first detection time period of the first modifiedd SID frame to the frame concerned, including said frame. The individual linking information thus interlinks successive DTMF frames (frames 1-4) relating to the same DTMF signal. At the receiving end, in receiving DTMF frames, it is calculated at each error-free frame how long the DTMF signal has been received. Only when the individual linking information of a received frame indicates the duration of the DTMF signal is longer than the threshold value, for instance 40 ms, the DTMF signal indicated by the frequency pair inforamtion of the received frames is generated to a subscriber station. During the waiting period, background noise is generated.
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