An application is permitted to specify its communication requirements at start of day and to modify those requirements during the lifetime of the stream.
Modules are sub-classed as sources, sinks, agents, filters, switches, gates, etc.
A module is a virtual processor much like a UNIX process, encapsulating host resources such as memory and CPU and providing an interface by which those resources may be controlled. Ports that send data to the stream are called plugs and ports that receive data from the stream are called sockets . The virtual concept of a stream is realised by the physical collection of two or more ports. Modules are manufactured by factory objects which are running on distributed hosts, each of them running one or more factories. Reliablity in the transport layer involves the detection and recovery of corrupted data by the receiver and the detection and retransmission of lost packets.