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.
Table 1: 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 |
