Source : Free On-Line Dictionary of Computing

Lower Layer Protocol
     
         (LLP, or lower-layer protocol)
        Any {protocol} residing in {OSI} layers one to four.
     
        These protocols package, {route}, verify and transmit
        {datagrams}.  A prime example would be {TCP/IP}.  Lower layer
        protocols support the {upper layer protocols}.
     
        (1999-02-17)