GIOP

GIOP stands for General Inter-ORB Protocol. It is the transport-agnostic wire protocol used by CORBA to enable communication between Object Request Brokers (ORBs). Standardized by the Object Management Group (OMG) as part of the CORBA specification, GIOP defines how messages are framed, encoded, and transported between ORBs, independent of the underlying network protocol.

Structure and encoding: Each GIOP message consists of a header that conveys protocol version and message length, followed by a body whose content is defined by the message type and encoded using the Common Data Representation (CDR). The protocol supports a small set of message types such as Request, Reply, LocateRequest, LocateReply, CancelRequest, and Fragment. Fragment messages enable the transmission of large requests or replies in chunks.

Transport mapping: Although GIOP is transport-agnostic, the most common deployment uses the Internet Inter-ORB Protocol (IIOP), which maps GIOP onto TCP/IP. Other transports may be used by specific ORB implementations.

Versioning and interoperability: GIOP defines multiple major.minor versions. Implementations negotiate compatibility during connection setup, enabling interoperability across vendors while allowing evolution of features.

Impact: GIOP provides the shared protocol that allows CORBA ORBs from different vendors to locate, marshal, and exchange requests and replies for distributed objects. It remains a foundational component of legacy CORBA deployments and influenced later middleware designs.

Implementations: Many open-source and commercial ORBs implement GIOP, including TAO, JacORB, omniORB, and various vendor-specific CORBA products.