# PPX terminology

An application can use the PPX service to:

- Manage connections.

- Make one-talker, one-listener switch connections.

- Perform actions on groups of connections in a single transaction.

The following table defines the basic elements of the PPX service:

Term | Definition
--- | ---
Connection object | An internal data structure maintained by the PPX server that is created when a switch connection is successfully opened. This structure records the state of the connection. In the PPX service, a connection object can be considered as an empty container until talkers and listeners are assigned to it.
Connection handle | An identifier for a specific connection object.
Connection | A logical path between two terminus entities. Within the PPX service, a connection can have only one talker but can support multiple listeners.
Terminus | A single access point to a switch block input or switch block output. A terminus contains a bus, a stream, a switch number, and a timeslot.
Talker | The terminus that drives the output on the connection.
Listener | The terminus that receives input from the connection.

## Properties of connections and listeners

PPX connections and PPX listeners have the following unique properties:

- Switch connections established through the PPX service have an ownership property.

When a PPX client creates a connection between two points, only the client that established the connection (who owns it) is allowed to break the connection (which disables output).

- Ownership can be overridden by assigning the connection a name, allowing different contexts bound to different clients to operate on the same connection points.

- PPX listener points have an associated state value which is either BUSY or NOT_BUSY.

Listener points that are connected to a talker are in the BUSY state. A listener point can be connected to a talker only when that point is in the NOT_BUSY state. Therefore, if talker point A is connected to listener point B, listener point B must be disconnected from talker A before it can be assigned to a new talker point C.