The YARP library supports transmission of a stream of user data across various protocols – TCP, UDP, MCAST (multi-cast), shared memory – insulating a user of the library from the idiosyncratic details of the network technology used.
We call these these low-level protocols the ``Carriers'', to distinguish them from the higher-level protocols we will be concerned with here.
For the purposes of YARP, communication takes place through
Connections'' between named entities calledPorts''. These form a directed graph, the ``YARP Network'', where Ports are the nodes, and Connections are the edges.
Each Port is assigned a unique name, such as ``/motor/wheels/left''. Every Port is registered by name with a ``name server''. The goal is to ensure that if you know the name of a Port, that is all you need in order to be able to communicate with it from any machine.
The purpose of Ports is to move ``Content'' (sequences of bytes representing user data) from one thread to another (or several others) across process and machine boundaries. The flow of data can be manipulated and monitored externally (e.g. from the command-line) at run-time. In other words, the edges in the YARP Network are entirely mutable.
A Port can send Content to any number of other Ports. A Port can receive Content from any number of other Ports. If one Port is configured to send Content to another Port, they are said to have a Connection. Connections can be freely added or removed, and may use different Carriers.
The YARP name server is a server that tracks information about ports. It indexes this information by name, playing a role analogous to DNS on the internet. To communicate with a port, the properties of that port need to be known (the machine it is running on, the socket it is listening on, the carriers it supports). The YARP name server offers a convenient place to store these properties, so that only the name of the port is needed to recover them.
Here are the specifications available in this document:
A YARP network consists of the following entities: a set of ports, a set of connections, a set of names, a name server, and a set of registrations.
Communication within a YARP network can occur between two ports, between a port and the name server, between a port and an external entity, and between the name server and an external entity.
The standard YARP companion utility can be used to create a name server, and also to act as an external entity for querying and modifying the YARP network.