ITP (Interactive Terminal Protocol) was an early PAD protocol for use over X.25 developed in the 1970s for use with UK GPO's EPSS (Experimental Packet Switching System, the predecessor of PSS). ITP predated Triple-X, and is a completely different protocol. Science and Engineering Research Council (SERC) also used ITP on SERCnet and continued developing ITP after EPSS, although it eventually gave way to Triple-X.
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