csOc3ClockSource is a read-write setting choosing whether this OC3 port's clock is generated internally or recovered from the incoming line signal. As with the DS3 clock source, exactly one end of an OC3 link should be the timing master; leaving both ends on the same setting leads to clock slips that show up as coding violations rather than a hard link failure. For example, when adding a new OC3 circuit where the carrier's SONET equipment is the timing source, an admin sets csOc3ClockSource to line so this port recovers timing from the incoming signal instead of fighting the carrier's clock.