This read-only octet string, up to 15 bytes, reports the DAPI actually received on this OTU4 (about 111.8 Gbit/s) line facility, compared internally against the expected DAPI to detect a mismatch. This gives an operator the received counterpart needed to diagnose exactly which destination identifier is arriving, when troubleshooting a destination-mismatch alarm. For example, a received DAPI on the OTU4 facility on slot 3 pointing to an unrelated site's identifier would explain a TIM alarm as the circuit terminating somewhere other than intended.