(1) In a network, it is the mechanism for transmitting data from point a to point b. It often refers to a distributed object protocol such as SOAP, CORBA or RMI, which is software only and which invokes the running of programs on remote servers.

The term is a bit confusing, because it sounds like the physical layer (layer 1) of the network that places the bits "onto the wire." In some cases, it may refer to this layer; however, it generally refers to protocols higher than the physical layer or even the next higher data link layer (layer 2) such as Ethernet and ATM. See OSI model, communications protocol, data link protocol and distributed objects.

(2) In an electronic system, it refers to the control signals (start and stop transfer) and architecture (serial, parallel, etc.) of the bus or channel that transfers data.