Protection of long-reach PON traffic

A resilience strategy is introduced for networks implementing dual homing (dual parenting) of customers, specifically those employing Long-Reach PONs (LR-PONs). Assuming that some mechanism exists to detect network element failures, the discussion concentrates on the protocols which propagate information about the reachability of LR-PONs and those that re-route traffic in the event of a fault. A protocol called FROTH (Fast Recovery for OLTs via Transmission of Hellos) informs each edge router which LR-PONs are available over the whole network. This information is used by another protocol called LATTE (Label and Address Tunneling via Tables at the Edge), to re-route traffic in the event of failure. A target of 50 milliseconds is assumed for end-to-end recovery time, since this has been used for many years with voice services, and is adopted in the absence of other information. Here, FROTH transports signaling traffic over IP - due to the probabilistic nature of packet transmission, it is impossible to place a hard bound on recovery time, but rather the probability is calculated that it will be met.Modeling studies suggest that in the event of a cable failure or single equipment element failure, re-routed data will almost always leave the transmitting edge router in under 50 milliseconds. For more catastrophic failures (such as router failure or loss of an edge router), recovery might take between 100 - 200 milliseconds. Reachability information for each LR-PON is distributed over each area of the network by IP, and used to activate re-routing of traffic via tunnels or address substitution. However the underlying services need not use IP, and may be of any type (for example private line), making the scheme separate from the service, customer or provider.