This configures which timing source the SONET interface's transmit side uses to generate its outbound clock signal - recovering it from the received signal (loop timing), using the device's own internal clock (local timing), or passing timing through from another interface (through timing). Administrators set this correctly to avoid clock slips and framing errors, since SONET networks require carefully coordinated timing hierarchies across all connected equipment. In a network where this device should follow the timing of its upstream neighbor rather than generate its own, an admin would set this object to loopTiming.