FXO Voice Subscriber Line 2247the calling number is sent to the IP network, and if the function is disabled, thecharacter "P" or "O" is sent.Busy Tone Detection In practice, there are various switches and these switches use different signalingstandards. Alike, the call progress tones played on these switches have differentindexes and spectral features. Therefore, it is impossible to identify the busy toneswith a fixed threshold value.The automatic busy tone detection adopts the intelligent busy tone identificationtechnology to obtain a set of parameters most reflecting a busy tone featurethrough sampling, calculation, and analysis of the input busy tone. You canconfigure these parameters on the FXO interface to accomplish the busy tonedetection, thereby resolving the problem that different switches have differentbusy tone indexes.Attention should be paid to the following three points from the detectionperspective:■ Busy tone frequency: Most busy tones contain one or two frequencies atpresent.■ Duty ratio: Duration ratio of high/low levels composing a busy tone signal, i.e.,the common called make-break ratio. Different countries or regions havedifferent specifications about the duty ratio of a busy tone. The nationalstandard of China is 350 milliseconds/350 milliseconds (10% error allowed).■ Detection threshold: threshold used to judge the signal energy. The signalenergy higher than the threshold is regarded a high level. Otherwise it isregarded as a low level.Figure 651 shows the typical network diagram for automatic busy tone detection.Telephone A is connected to PBX A that connects to the FXO interface of Router Avia an ordinary telephone line. The connection of the peer end is similar.Figure 651 Network diagram for automatic busy tone detectionPerform an automatic busy tone detection test as follow:1 Use Telephone A (010-1001) to dial the number 1002. The FXO interface onRouter A plays a dial tone to PBX A, which then transmits the tone to Telephone A.Then dial the number 07552001. Telephone B rings. After Telephone B 2 is pickedup, the call is connected.2 Hang up after hearing the access tone. At this time, PBX B plays a busy tone toRouter A through a line.WANPBX A PBX BTelephone A010-1001 Telephone B0755-2001Router A Router B1002FXO FXO2002
