f 100 per S, and 30 ms without receiving a CC message triggers a failover switch. There are four main APS variants (ITU-T G.808.1): In 1+1, APS-protected traffic is always sent over both paths, but the destination end consistently selects packets from one path until a failover is triggered. In 1+1 no APS signaling is required and failover time is little more than the detection time, but network bandwidth is wasted on redundant traffic. In 1: 1, APS-protected traffic is sent only over the working path, leaving the backup path free to carry unprotected pre-emptible traffic. Upon detecting failure of the working path, the tail end signals the head end (over an APS signaling channel) to commence sending the traffic over the backup path. This mechanism is more efficient in use of network resources, but requires both an APS signaling channel and additional time before failover switching is accomplished. 1:1 APS systems may revert to the original state after the working channel has been repaired, although this may cause an unnecessary short service disruption. Yet more efficient is n APS, where a single backup channel is used to protect n work- ing channels, with the drawback that two failures can't be handled. 1:n APS requires two-phase signaling, where the tail end signals the head end of failure, and the head sig- nals back that the backup channel is available and the switch has been made. 1 : n systems will almost always revert upon repair. Finally, in m:n APS m working channels are protected by a smaller number n of standby channels, enabling protection in the case of up to n simultaneous failures, at the expense of a three-phase APS signaling protocol. The second prevalent self-healing mechanism, FRR, is frequently used in MPLS core networks (RFC 4090), although recent work has extended this method to IP net- works (under the name Loop Free Alternates (LFA) (RFC 5286)) and to segment routing (under the name Topology Independent Loop Free Alternates (TI-LFA) (draft-ietf-rtgwg-segment-routing-ti-lfa)). Unlike APS wh