First world standard in digital format. First optical Interfaces.Transversal compatibility reduces networking cost. Multivendor environment drives price down. Flexible synchronous multiplexing structure .Easy and cost-efficient traffic add-and-drop and cross connect capability. Reduced number of back-to-back interfaces improve network reliability and serviceability.Powerful management capability.New network architecture. Highly flexible and survivable self healing rings available.Backward and forward compatibility: Backward compatibility to existing PDH. Forward compatibility to future B-ISDN, etc.