File Name Protection in SONET/SDH Topologies / Mechanisms Available 1+1 Linear APS UPSR BLSR 2-fiber Restoration channels must be reserved, reducing protected capacity 4-fiber -- two sets of Tx/Rx fibers for each line interface Span Switch: Can restore by utilizing alternate Tx/Rx fibers Ring Switch: Utilizes restoration channels located on a separate ring Extra Traffic possible APS, BLSR signaling done in K0 / K1 bytes of overhead
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