In some cases the requirement exists to prevent a MEP from entering the defRemoteCCM defect, remote peer timeout, from more time than the standard 3.5 times the CCM-interval. Both the IEEE 802.1ag standard and ITU-T Y.1731 recommendation provide a non-configurable 3.5 times the CCM interval to determine a peer time out. However, when sub second CCM timers (10ms/100ms) are enabled the carrier may want to provide additional time for different network segments to converge before declaring a peer lost because of a timeout. To maintain compliance with the specifications the ccm-hold-timer down <delay-down> option has been introduced to artificially increase the amount of time it takes for a MEP to enter a failed state should the peer time out. This timer is only additive to CCM timeout conditions. All other CCM defect conditions, like defMACStatus, defXconCCM, and so on, maintain their existing behavior of transitioning the MEP to a failed state and raising the correct defect condition without delay.
When the ccm-hold-timer down delay-down option is configured the following calculation is used to determine the remote peer time out (3.5 times the CCM-Interval + ccm-hold-timer delay-down).
This command is configured under the association. Only sub second CCM enabled MEPs support this hold timer. Ethernet-Tunnel Paths use a similar but slightly different approach and continue to use the existing method. Ethernet-tunnels are blocked from using this new hold timer.
It is possible to change this command on the fly without deleting it first. Simply entering the command with the new values changes the values without having to delete the command before the change.
It is possible to change the ccm-interval of a MEP on the fly without first deleting it. This means it is possible to change a sub second CCM enabled MEP to 1 second or above. The operator is prevented from changing an association from a sub second CCM interval to a non-sub second CCM interval when ccm-hold-timer is configured in that association. The ccm-hold-timer must be removed using the no option before allowing the transition from sub second to non-sub second CCM interval.