The SEQ_CNT field is a 16-bit field that identifies the position of the frame in its sequence:
• SEQ_CNT is 0 for the first frame and is then incremented for each frame.
• The sequence recipient can use SEQ_CNT to determine the correct order of the frames in the sequence.
• The sequence recipient can use SEQ_CNT to confirm that all frames in the sequence were received and to detect missing frames.
Only one sequence can be active at a time within a single exchange. A Sequence Initiator must complete transmission of data frames for a sequence before the other node can send another sequence for the same exchange. The Exchange Originator and Responder must coordinate control of the exchange; control over the exchange is called the Sequence Initiative. However, a port can transmit sequences for different exchanges concurrently. This is one form of multiplexing that is supported by Fibre Channel.