Agent Invocation Transport Protocol (AITP)

The Agent Internet Protocol (AIP) provides best-effort, name-based datagram delivery between autonomous AI agents identified by agent:// URIs. The Agent Invocation Transport Protocol (AITP) is a message- framed invocation and streaming transport above AIP. Unlike traditional host-to-host transports (TCP, QUIC) that operate on socket endpoints and byte streams, AITP is natively message- framed, method-aware, and association-aware: its header carries a method name as a first-class field, and its protocol data units are discrete requests, responses, stream chunks, and control segments exchanged between named agents. AITP is not a byte-stream transport; it is an agent-native invocation and streaming transport that carries method names, request/response correlation, flow control, and session semantics natively in its header — so that upper-layer agent protocols need not reinvent them. AITP intentionally includes a minimal generic invocation outcome space (four dispatch- level status codes); richer application semantics belong in the response body or upper-layer protocols. Unlike transport bindings that adapt existing agent protocols to HTTP, gRPC, or MOQT, AITP defines a common invocation substrate directly above AIP, with association state, request-concurrency flow control, and method-aware framing as first-class transport concerns. AITP is best understood as a common invocation substrate above AIP, not as a byte-stream transport analogue. This document specifies the AITP segment format, segment types, status codes, flag bits, TLV options, association state machine, reliability engine, flow control, circuit-breaker mechanism, streaming, orderly close and abort, and interfaces to AIP below and application protocols above.