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Intermittent echo on analog voice port calls

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Core Issue

The echo is caused by an impedance mismatch with the local Telco.

Resolution

An impedance of 600 ohms real is standard for most Telcos and PBXs. Therefore, a problem with impedance mismatches is rare.

However, there are differences. For example, some PBXs use 900c. If the impedance is set incorrectly (if there is an impedance mismatch), a significant amount of echo is generated. This echo could be masked if the echo cancel command is issued.

In addition, gains might not work correctly if there is an impedance mismatch. You can configure impedance in Cisco IOS  Software by issuing the impedance voice port command.

Problem Type

Voice quality problems (Audio quality: Choppy voice, hissing, echo, etc.)

Voice Quality

Echo (Listen to short or long echo samples.)

Frequency and Scope of Symptom

Occurs intermittently

Occurs only on some calls

End Where Problem is Heard or Device Type Involved

Both ends

Call Topology and Direction

IP network > PSTN/PBX/gateway > IP network

PSTN/PBX/gateway > IP network > PSTN/PBX/gateway

TDM Signaling Type

Analog

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