This OCTET STRING value (default 0.2) sets the transmitter's pulse-shaping filter roll-off factor for the coherent optical channel (och-os) on the line side of a pluggable transceiver, a coherent-optics parameter controlling how sharply the transmitted spectrum is shaped at its edges. An administrator adjusts this to trade spectral width against signal-to-noise performance, tightening the roll-off to pack channels more closely on a crowded DWDM grid. For example, lowering the roll-off factor from the default on och-os would narrow the occupied spectrum, which matters when trying to fit more channels into a fixed amount of available optical bandwidth.