message signal unit (SS7) (MSU)

A Message Signal Unit(MSU) is a character input message in the SS7 signaling.

The MSU message is used for connection control, queryingdatabases, network management, network maintenance and routing labels with the various point codes(PCs). The Message Signal Unit consists of the Message Transfer Part( MTP) and two additional data fields: The Service Information Octet( SIO) and the Signaling Information Field( SIF).

Structure of the Message Signaling Unit (MSU)

The Service Information Octet shows the protocol type at level 4, for example the Telephony User Part( TUP), ISDN User Part( ISUP) and whether the protocol types are national or international standards. The Signalling Information Field (SIF) contains the control information and the routing labels. The SIF data field can be up to 272 octets long and is used by all Level 4 protocols.