link level protocol (LLP)
The LinkLevelProtocol (LLP) is an asynchronous backup protocol ( BSC variant with BCC checksum) in Datex-J for analogdata transmission ( text mode) from the Datex-J exchange to the user's terminal equipment ( software decoder). There is no secured transmission in the opposite direction. For two-way transmission security on switched modem connections(a/b interface), the Datex-J provides the well-known protocols ITU- TV.42 and Microcom Networking Protocol ( MNP) in version MNP 4. For system access via the ISDN connection, transmission security is provided using the familiar HDLC procedure.