By late 1980 the DoD had adopted TCP/IP and the ARPANET's terminal support (Telnet) and File Transfer (FTP) Protocols as DoD standards. In 1981 planning began for all ARPANET hosts to transition to TCP/IP. The official transition completion date was to be January 1, 1983; in fact the transition was not completed for several more months.
The conversion to TCP/IP was mandated to make it possible to split ARPANET into multiple networks without disrupting host computers’ ability to communicate with one another regardless of which network they were assigned to. The networks were to be connected by mail bridges. These devices were customized routers that could filter out undesirable traffic – in essence, the first firewalls. The mail bridges were built and operated by BBN, making BBN the first Internet router vendor, and putting BBN in the center of the early development of IP routing protocols.