Echo-Return Loss (ERL) and Single-Frequency Return Loss (SFRL) performance are usually dominated by termination and/or loop input impedances. The system provides an acceptable level of echo performance if the ERL and SFRL are met, as shown in the table.
ERL and SFRL performances by connection type
Type of connection
ERL and SFRL performance
Station-to-station
ERL should meet or exceed 18 dBSFRL should meet or exceed 12 dB
Station to 4-wire trunk connection
ERL should meet or exceed 24 dBSFRL should meet or exceed 14 dB
Station to 2-wire trunk connection
ERL should meet or exceed 18 dBSFRL should meet or exceed 12 dB
4-wire to 4-wire trunk connection
ERL should meet or exceed 27 dBSFRL should meet or exceed 20 dB
