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Cisco Bug: CSCur40235 - SPA122/112: New Echo Cancellation Parameters for Hughes

Last Modified

Jan 20, 2015

Products (1)

  • Cisco Small Business IP Phones

Known Affected Releases

7.5.7(1)

Description (partial)

Symptom:
Preliminary Requirements from Hughes:

Echo Return Loss Enhancement (ERLE): the capability of the Echo Canceler to reduce the residual echo, e(n). The bigger the ERLE, the better the performance of the EC.
Convergence Time: is the time required by the EC to achieve the optimum (maximum) ERLE.
Double Talk (DT): is a condition where the near-end user talks at the same time when the echo presents.
Tail delay: is the distance between the EC and the Hybrid in term of time.
Center-clipper or Non-linear Processor: a feature of EC to completely shut-off the Transmit (Tx) line if the ERLE has reached the optimum value and there is no near-end signal.
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For satellite communication in which the delay between two parties are large, around 500ms, one way, Echo Cancellation needs to have the following specifications:
Large ERLE: about 40 dB 
Quick convergence time so that the Echo signal can be canceled quickly
Quick Double Talk (DT) detector: since DT condition can corrupt the EC filter coefficient, EC should employ a good and quick DT so that the EC coefficients are not corrupted. Note that the corrupted EC coefficients will reduce the ERLE.
If the Time Delay, delay between hybrid and the EC, is large, the number of EC coefficient should be able to handle this time delay.
Comfort noise is required to make sure when the Center Clipper is active, the user does not have the perception that the line is dead.

Conditions:
Hughes uses a satellite network where the ATAs access the internet through satellite. The latency is higher than a terrestrial network.
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