In distributed computing, GIOP (General Inter-ORB Protocol) is the abstract protocol by which ORBs communicate.

IIOP (Internet Inter-Orb Protocol) is the implementation of GIOP for TCP/IP.

The OMG defines three parts of GIOP:

• the Common Data Representation (CDR) - transfer syntax mapping OMG IDL data types into a low-level representation for “on-the-wire” transfer between ORBs and Inter-ORB bridges.
• message formats - messages are exchanged between agents to facilitate object requests, locate object implementations, and manage communication channels. Messages are:
  • Request
  • Reply
  • CancelRequest
  • LocateRequest
  • LocateReply
  • CloseConnection
  • MessageError
• message-transport assumptions
  • connection orientated
  • reliable
  • can be viewed as a byte stream
  • provides some reasonable notification of disorderly connection loss
  • model for initiating connections can be mapped onto the general connection model of TCP/IP.