Distributed call system

<B> DISTRIBUTED CALLING SYSTEM <D>. A telephone service is provided using a distributed architecture that employs a group of resources, each of which exposes a hierarchical namespace. The architecture includes two fundamental types of resources, the device server and the call coordinator, which are interconnected over a network using a common protocol, for example, TCP-IP. The interaction between the various resources follows "client-server" principles to implement end-to-end communication. Device servers represent physical / logical telephone devices, which include a) endpoint device servers and b) port device servers. Endpoint device servers 1) represent controls for communication, such as keyboards, indicator lamps, and display devices, and 2) perform media execution, for example, voice reconstruction, transport and digitization. Port device servers have two "sides". One side is implemented to appear to a call coordinator as s if it were a device server, and the other side has an interface adapted to function interconnected with a pre-existing telephone service core. In the term "device server", "server" is used in the conventional way of the "client-server" architecture, where the server responds to a request from clients and does not take action unless it is in response to a client request. . A call coordinator works in the role of the "customer". Device servers are unaware of the communication state, which is maintained by the call coordinator and exposed as a hierarchical namespace. The call coordinator treats the processing of a call as a sequence of steps, each of which can be implemented by a small portion of computer executable code called a resource "applet".