forward sequence number (SS7) (FSN)

Structure of the Message Signaling Unit (MSU)

Forward Sequence Number(FSN) is a data field in the Message Transfer Part ( MTP) of the Message Signal Unit( MSU) in SS7 signaling. The FCN data field contains 7 bits and is used to number the character units with forward sequence numbers from 0 to 127. This allows the receiving station to control and acknowledge the character sequence. The Forward Sequence Number together with the 1-bit Forward Indicator Bit( FIB) data field forms an octet.