V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

LLP
       Link Level Protocol (BTX)


The Free On-line Dictionary of Computing (30 December 2018):

Lower Layer Protocol
LLP

    (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)