Low Entry Networking (LEN) defines functions and protocols for the PU-2.1 physical unit in the SNA architecture that support partner-to-partner communication. SNA LEN enables communication between PU 2.1 nodes that are directly connected to each other. PU
2.0 is a subset of PU 2.1. Low Entry Networking (LEN) has been superseded by Advanced Peer to Peer Networking (APPN).