Softswitch - Definition
A Softswitch is a central device in a telephone network which connects calls from one phone line to another, entirely by means of software running on a computer system. This work was formerly carried out by hardware, with physical switchboards to route the calls. A Softswitch is typically used to control connections at a junction point between circuit and packet networks. A single device containing both the switching logic and the switching fabric can be used for this purpose; however, modern technology has led to a preference for decomposing this device into a Call Agent and a Media Gateway.
The Call Agent is responsible for functions like billing, call routing, signalling, call services, etc. A Call Agent may control several different Media Gateways in geographically dispersed areas over a TCP/IP link. The Feature Server, often built into a Call Agent / Softswitch, is the functional component that provides call-related features. Capabilities such as call forwarding, call waiting, and last call return, if implemented in the network, are implemented in the feature server. The feature server works closely with the call agent, and may call upon the media server to provide these services. These features do not require the subscriber to explicitly request them but tend to be triggered within the call handling logic.
In IP Multimedia Subsystem (IMS) networks, the Softswitch element is represented by a combination of different CSCF (Call Session Control Function) elements and Media Gateway Controller (MGC) elements.
In the pure SIP environment, SIP makes use of elements called proxy servers to help route requests to the user's current location, authenticate and authorize users for services, implement provider call-routing policies, and provide features to users.