Out‑of‑service measurements are performed when the E1 circuit is not in-service or is inactive. Typically these tests are done during initial installation, during circuit acceptance by the wireless service provider, or when the results of the in‑service measurements indicate errors. These measurements provide detailed information on the E1 circuit.
Out‑of‑service testing is performed using end‑to‑end testing, which requires a technician and an E1 tester at each end of the circuit, or by establishing a loopback at the remote end of the circuit.