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Guiding Assumptions Can’t assume U-PEs have full S-PE/U-PE reachability info Signalling launched by downstream U-PE For PWs, can’t know full path until label mapping has reached T-UPE Informed selection of PW path by upstream U-PE who has service knowledge and view of network path/resources L2VPN service depends on selection of underlying PW network resources Each hop selects next hop, either: Controlled path discovery (not flooding) Blind path search (mandates “crankback”) Crank back to the source vs. Hop-by hop crank back Requires source routing to be effective, but don’t have full path info Objective is to minimise crank back Same forward and reverse path for OAM Ability to auto-provision backup path |