This read-only INTEGER reports whether the coherent optical channel (och-os) on the line side of a pluggable transceiver is currently using non-differential or differential line encoding. An administrator uses this to confirm the coherent optics have come up in the encoding mode expected for the provisioned modulation format and FEC combination, since a mismatch here typically prevents the far end from decoding the signal at all. For example, confirming differential encoding is active on och-os after a transceiver swap helps rule out an encoding-mode mismatch as the cause of a link that will not synchronize.