ge to the ingress and sends a PathErr upstream indicating that the state has been removed. The PathErr propagates upstream with the next two nodes and does not set the State Removed flag. Farther upstream, an LSR decides to reenable the GMPLS in Optical Networks Figure 8-5 Notify Tearing state with PathErr. PathErr PathErr PathErr PathErr Path Tear (State_removed) (State_removed) Path Tear Path Tear Figure 8-6 Notify Notify Tidying up in a fragmented network. PathErr PathErr PathErr PathErr Path Tear (State_removed) (State_removed) (State_removed) Path Tear State Removed flag and SO also sends a PathTear downstream. Just one node away from the ingress, the PathErr traveling upstream meets a PathTear traveling downstream and no further processing is required. This feature can be useful to tidy up when the network is fragmented (see Figure 8-6). Upstream of the LSP failure on the left-hand side of the diagram, the processing is much like that described for Figure 8-5. The com- bination of PathErr (with or without the State Removed flag set) and PathTear (triggered by the Notify or the PathErr) causes the removal of state in a timely manner. Downstream of the break, however, RSVP only provides for state removal through Path refresh timeouts. The LSR that detects the error might send Notify or ResvErr, and the egress might send ResvTear, but these exchanges do not fully remove the state or reservations at the inter- mediate nodes. Further, the PathTear sent by the ingress will never reach the LSRs downstream of the LSP failure if that failure affects the control path as well as the data path. This situation can be remedied by using the State Removed flag on the PathErr message (see Figure 8-6). When it receives the Notify message, the egress LSR can remove state, deprogram its switch, and release reserva- tions. It then sends the PathErr upstream, indicating that it has removed state, and the fragmented LSP is tidied up. Chapter 8 8.5 Bidirectionality Trunks through the core of an optical network often need to be bid