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How does the echo canceller interpret a signal when the ERL value is too low?
A. The echo canceller treats the signal as echo and applies the configured values.
B. The echo canceller considers the signal returning to the gateway as comfort noise generated during periods of silence and does not act on it.
C. The echo canceller will apply the maximum echo-cancel coverage time to the signal to determine if this is echo or voice.
D. The echo signal retuning to the gateway is too loud and the echo canceller interprets it as normal voice instead of echo.
Correct Answer: D
Explanation/Reference:
Explanation:
Insufficient echo return loss (ERL) to handle the echo might cause these problems:
Echo canceler does not cancel, but not enough to make echo inaudible. If the ERL value is too low, the total echo return loss seen by the IP network (ACOM) might be insufficient to suppress the echo. ERL needs to be approximately 20 dB (at least 15 dB)
Echo canceler does not cancel. If the ERL value is too low, the echo signal that returns to the gateway might be too loud (within 6 dB of the talker signal). This causes the echo canceler to consider it as voice (double-talk) instead of echo. As a consequence, the echo canceler does not cancel it.
ERL needs to be approximately 6 dB or higher for the echo canceler to engage. In Cisco IOS Software Release 12.2.13T, you can configure this ERL level. See theEcho Canceler Enhancements in Cisco IOS Software Releases 12.2.11T and 12.2.13Tsection of this document. http://www.cisco.com/en/US/tech/tk652/ tk698/technologies_tech_note09186a0080149a1f.shtml
