PIKA FormulaT1/E1, Руководство пользователя

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Echo tail length specifies the maximum amount of time difference between the source signal and the echo signal. For example,
when the maximum tail length is set to 12, the echo canceller can remove an echo signal that occurs up to 12 ms after the original
source signal occurs.
The default tail length is 12 ms. This means that echo cancellation cancels any echo that has a round trip delay from the echo
canceller reference input back to the echo canceller of less than 12 ms. A 12 ms tail length is normally sufficient if a call is not a long
distance call. For long distance connections, an extra 1 ms of tail length needs to be added to the base of 8 to 12 ms for every 55
miles of distance between the caller and the echo canceller. This distance is not a straight-line distance, but rather the length of the
path followed by the audio signal. The default tail length of 8 to 12 ms accounts for the smearing of the echo signal, network
switching delays, and ATM packetization delay if ATM is used in the network. Note that the tail length should not account for any
IP network delay in VoIP, since the IP network should never be in the echo path for VoIP applications.
The optimal tail length is the maximum echo round trip echo delay. If the tail length is shorter, the portion of the echo delayed by
an amount greater than the tail length is not canceled, resulting in a louder residual echo. If the tail length is longer than needed,
echo cancellation adapts somewhat more slowly than it would for an optimum tail length. A longer than needed tail length also
results in a somewhat louder residual echo. This is not normally noticeable, particularly if echo suppression is used. A longer than
needed tail length uses unnecessary CPU resources. Generally, the echo tail length is too short if increasing the tail length results in a
noticeably reduced residual echo level (with echo suppression disabled). There are some applications, such as DTMF detection, that
may not require the elimination of all echo. In this case, very short tail lengths in the range of 2 to 8 ms may be useful. Normally,
echo cancellation tail length is set to the maximum required tail length.
6.4.3 Call Analysis Configuration
The gateway can, under the control of an incoming SIP call, perform call analysis on the outgoing call, and report the result back to
the originating SIP endpoint. The following parameters are used to configure Call Analysis.
Speech
Debounce
On Minimum time (in milliseconds) of continuous speech before a sound segment is recognized as speech. Filters out
short clicks, tones, and noise. [30 to 300 ms; default: 250 ms]
Speech
Debounce
Off Minimum time (in milliseconds) specified to filter out short periods of time where no speech is detected, for example,
a short pause between words. Only if speech is not detected for longer than Speech Debounce Off, is an end of
speech segment declared. [30 to 300 ms; default: 250 ms]
Live
Person
Words Maximum number of live person words. A larger number of words is considered to come from an answering
machine. [1 to 10; default: 3]
Max
Duration: In milliseconds. Default value = 2000
6.4 ISDN Settings Screen PIKA FormulaT1/E1 Gateway 1.0 User Guide Call Analysis Configuration
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