ops. Open loop mechanisms are generally incompatible with QoS assurance, and closed loop mechanisms have not gained wide acceptance. For MPLS-TP the IETF has standardized linear protection (RFC 6378) and ring protection (RFC 6974), and the ITU-T has standardized alternative mechanisms (ITU-T G.8131, ITU-T G.8132). More prevalent is MPLS Fast ReRoute (RFC 4090) that provides a local detour around failed fibers or nodes at the cost of loss of determinism - the endpoints are not informed of the local route change. IP recovers from failures by computing new routes, which is often a lengthy process. Loop Free Alternate Fast Reroute (RFC 5286) minimizes downtime by precomputing backup paths (called repair paths) that are guaranteed to be loop free. For IP (MPLS) an LFA to a destination with respect to an element (link/node) for a destination is a router that: 1. Is not the default next hop; 2. Is connected to the destination; 3. Does not forward through the element (and hence does not need to know about the failure). In the context of MPLS segment routing, topology independent LFA (TI-LFA) allows the source LSR (which knows all the labels from the SR protocols) to immediately substitute and alternative MPLS-SR label stack. It is topology independent in the sense that a loop free backup path is found irrespective of the topologies before and after the failure. The replication and erasure mechanisms (FRER, PREOF) discussed above have been specified by TSN for Ethernet (802.1CB) and are being specified for IP and MPLS by DetNet (RFC 8655). 6.6.5.4.6 Fault Management Unless the failed element is physically connected to the destination, triggering any of the reliability mechanisms of the previous subsection relies on E2E continuity monitoring mechanisms. (Note that CC refers to verifying that information sent indeed arrives at the destination, while connectivity verification (CV) refers to verifying that information sent to a particular destination does not arrive somewhere else.) These continuously running OAM mechanisms, 