In network systems for transporting GFP-encapsulated FICON frames across a SONET/SDH transport network between FICON ports, the transport interfaces for the FICON ports operate to drop duplicate and out-of-order frames transported across the SONET/SDH network. The transmitting transport interface inserts a sequence number incremented with each FICON frame into said one or more transport frames, whereby the sequence number is used as an index for determining duplicate and out-of-order frames after transport over said SONET/SDH network. The receiving transport interface compares sequence numbers with each FICON frame to determine duplicate and out-of-order FICON frames, drops the duplicate and out-of-order FICON frames; and sends the balance of the compared FICON frames to the receiving FICON port.