Interface message processor
(also IMP)
Interface message processor definition
An interface message processor is a specialized computer that was used to connect networks to the ARPANET (Advanced Research Projects Agency Network). Interface message processors were the first examples of packet routers. Interface message processors were largely phased out of service after ARPANET was decommissioned in 1989.
The first interface message processors were built by Bolt Beranek and Newman Inc. (now Raytheon BBN) in 1969 based on Honeywell DDP-516 minicomputers. Their development was a significant milestone in the history of computer networking, as it allowed multiple networks to communicate with each other for the first time.
See also: data packet, packet switched network, customer edge router
How interface message processors work
An interface message processor sits between multiple host computers on a network and acts as a gateway for data transfers to other networks. Interface message processors are connected to host computers using dedicated communications lines.
A host computer wishing to send data to a computer on a different network must first send it to the interface message processor. The interface message processor then encapsulates the data into packets and transmits it to the destination network, either to another processor or directly to the target computer.