RFC 441 Inter-Entity Communication January 1973 +------+ | USER | | TTY | +------+ | | -------------|---|--------------+ | | | +-------+ +------------------+ | | HOST | | COMMAND | | | A | | INTERPRETER | | +-------+ +---+-+-------+-+--+ | | TTY |_| |_| TTY | | OUT-PORT ^ | IN-PORT | | | | | | | V | +--------------+ | +-|-+ | | <----| |IN-PORT |--+ +-|-+ | | | CONSULTANT | | | #1 | +-|-+ | I.E.C. ---->| |OUT-PORT | +-|-+ | | +--------------+ | | +--------------+ +-|-+ | <----| |IN-PORT |--+ +-|-+ | | | | CONSULTANT | | | | #2 | | +-|-+ | | ^ | ---->| |OUT-PORT | | | | +-|-+ | | JOB | V JOB | +--------------+ | IN-PORT+--+ +--+OUT-PORT | | -----|--|-------|--|----------+ | +----+ +-------+ +---------+ | | | +------+ | USER JOB | | HOST | | B | +------+ The user now has the option of opening or closing any of the ports he wishes. While in conversation mode, he might turn off the ports leading to the JOB. If he wished consultant 1 to control the job, he might turn off the input ports from his own TTY and from consultant 2. Bressler & Thomas