In circuit-switched telephony, echo can be caused by acoustic reflection in the remote party environment or by electrical reflection from 2-wire to 4–wire analog-hybrid impedance mismatches. Impedance mismatch can occur in analog telephones and analog line/trunk cards, electrical cross-talk in circuitry, or in telephony wiring particularly in low-cost headsets. Due to this impedance mismatch that causes echo, the circuit-switched analog and digital telephones are implemented with a relatively large transmit loss. In principle, the transmit loss of telephones can be made very large followed by signal amplification in the receiving telephone. In practice, however, the transmit loss must be limited to prevent the electrical voice signal from dropping below electrical background noise. This has resulted in the adoption of transmit loss and receive loss values around 8 dB and 2 dB, respectively, although country-specific values can deviate from these values.

The loss plan administration that Communication Manager provides is primarily intended to control signal losses in telephones and gateways and not intended to control echo. However, in case of severe echo, the administered loss plan can be changed to a different plan. An increase in loss by a certain amount between two endpoints decreases the echo level by twice this amount. You must use this method of loss plan administration only after consulting Avaya Services personnel. To reduce echo, you must use echo cancellers with Avaya products.