(Link Support Layer) A common interface for network drivers. It provides a common language between the transport layer and the data link layer and allows different transport protocols to run over one network adapter or one transport protocol to run on different network adapters.

Instead of directly calling a particular data link protocol, the transport protocol calls the LSL library. Thus, any LSL-compliant network driver can provide data link services in that protocol stack. LSL is part of Unix System V. It is also the basis of Novell and Apple's ODI specification. See ODI and STREAMS.