To provide services without a physical switch, a softswitch is connected to a server (a Sun Microsystems or Unix machine, for instance) that runs the application. A softswitch is also connected to a media gateway, which is the element that physically connects to the PSTN, IP network or ATM network.

A softswitch is also known as a call agent, a call server or an MGC. It is a device that provides the traditional call control functions or switching matrix of a Class 4 and Class 5 switch. In a mobile network, a softswitch is also called a mobile switching center (MSC). At minimum, a softswitch provides:

• Intelligence that controls connection services for a media gateway or native IP endpoint.

• The ability to select processes that can be applied to a call.

• Routing for a call in the network, based on signaling and customer database information.

• The ability to transfer control of a call to another network element.

• Interfaces to, and support for, management functions, such as provisioning fault-tolerant billing.

• Support for multiple protocols, including some subsets of MGCP, Media Gateway Control Protocol (Megaco), SIP, SS7, call processing language, H.323 and Q.931/Q.2931.

• DiffServ, Resource Reservation Protocol, Real-Time Transport Protocol, Real-Time Control Protocol, MPLS and Institute of Electrical and Electronics Engineers (IEEE) 802.11p.

• Compliance/interoperation with some subsets of standards from the International Telecommunication Union (ITU), Internet Engineering Task Force (IETF), Frame Relay Forum, ATM Forum, IEEE’s IMS Forum and 3GPP/3GPP2.