The System Packet Interface (SPI) family of Interoperability Agreements from the Optical Internetworking Forum specify chip-to-chip, channelized, packet interfaces commonly used in synchronous optical networking and Ethernet applications.
The family of System Packet Interfaces is the most important packet-oriented, chip-to-chip interface family used between devices in the Packet over SONET and Optical Transport Network, which are the principal protocols used to carry the internet between cities.
This protocol has been developed by Optical Internetworking Forum (OIF) and is fast emerging as one of the most important integration standards in the history of telecommunications and data networking.
The Interlaken protocol, a close variant of SPI-5 replaced the System Packet Interface in the marketplace.
SPI 4.2 supports a data width of 16 bits and can be PHY-link, link-link, link-PHY or PHY-PHY connection.