Interface Message Processor

The Interface Message Processor (IMP) was the packet switching node used to interconnect participant networks to the ARPANET from the late 1960s to 1989. It was the first generation of gateways, which are known today as routers.^[1][2][3] An IMP was a ruggedized Honeywell DDP-516 minicomputer with special-purpose interfaces and software.^[4] In later years the IMPs were made from the non-ruggedized Honeywell 316 which could handle two-thirds of the communication traffic at approximately one-half the cost.^[5] An IMP requires the connection to a host computer via a special bit-serial interface, defined in BBN Report 1822. The IMP software and the ARPA network communications protocol running on the IMPs was discussed in RFC 1,^[6] the first of a series of standardization documents published by what later became the Internet Engineering Task Force (IETF).