IL2P (Improved Layer 2 Protocol) is a data link layer protocol originally derived from layer 2 of the X.25 protocol suite and designed for use by amateur radio operators. It is used exclusively on amateur packet radio networks.
IL2P v0.2 occupies the data link layer, the second layer of the OSI model. It is responsible for establishing link-layer connections, transferring data encapsulated in frames between nodes, and detecting errors introduced by the communications channel.
The Improved Layer 2 Protocol (IL2P) was created by Nino Carrillo, KK4HEJ, based on AX.25 and implements Reed Solomon Forward Error Correction for greater accuracy and throughput than either AX.25 or FX.25. Specifically, in order to achieve greater stability on links exceeding speeds of 1200 baud.
The specification itself outlines several design goals including:
- Forward error correction
- Eliminating bit-stuffing
- Streamlining the AX.25 header format
- Improved packet detection in the absence of Decode (DCD) and for open-squelch receive
- Produce a bitstream suitable for modulation on various physical layers
- Avoid bit-error-amplifying methods (differential encoding and free-running LFSRs)
- Increase efficiency and simplicity over FX.25 Forward Error Correction