This read-only integer holds the ifIndex of the physical link the near end uses as its timing reference for recovering the receive-direction IMA data cell clock toward the ATM layer. As with its transmit-direction counterpart, admins use it to identify which specific link is serving as the clock reference on the receive side, useful when isolating timing-related IMA group instability. For example, an admin troubleshooting intermittent group failures would check whether this reference link matches a link known to have marginal signal quality.