| 摘要 |
Control and status information between a mobile device and another device can be signaled over a voice channel using DTMF tones, e.g., a pre-defined sequence of DTMF tones can signal a desired message (more generally, a feature code). Tones sent are separated from each other by a time gap (T gap timer). If a receiving device does not receive a sequence of DTMF tones that can be matched to stored definitions of feature codes, then the receiving device generates a negative ACK. Also, if the sending device does not receive either negative or positive ACK, then sending device resends all tones of the feature code after a retry delay (T retry timer). Rather than having the T retry timer start when tones for a feature code start to be transmitted, the T retry timer is started after the T gap timer expires for the last tone of a feature code. Thus, only one timer is running (either T gap or T retry ), rather than having multiple timers running concurrently. Race conditions between the timers are avoided. |
