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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. For other uses, see Telephone (disambiguation). ...

A softswitch is typically used to control connections at the 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 takes care of functions like billing, call routing, signalling, call services and so on and is the 'brains' of the outfit. A Call Agent may control several different Media Gateways in geographically dispersed areas over a TCP/IP link. A Media Gateway Controller (MGC) is a system used in certain Voice over IP telephony architectures. ...

The Media Gateway connects different types of digital media stream together to create an end-to-end path for the media (voice and data) in the call. It may have interfaces to connect to traditional PSTN networks like DS1 or DS3 ports (E1 or STM1 in the case of non-US networks), it may have interfaces to connect to ATM and IP networks and in the modern system will have Ethernet interfaces to connect VoIP calls. The call agent will instruct the media gateway to connect media streams between these interfaces to connect the call - all transparently to the end-users. A Media Gateway acts as a translation unit between disparate telecommunications networks such as PSTN; Next Generation Networks; 2G, 2. ... The public switched telephone network (PSTN) is the network of the worlds public circuit-switched telephone networks, in much the same way that the Internet is the network of the worlds public IP-based packet-switched networks. ... Digital signal 1 (DS1, also known as a T1) is a T-carrier signaling scheme devised by Bell Labs. ... In telecommunications, T-carrier is the generic designator for any of several digitally multiplexed telecommunications carrier systems originally developed by Bell Labs and used in North America and Japan. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... STM is the INFORMATION STRUCTURE, used to support information pay load and overhead information field, organized in a block frame structure which repeats every 125 micro seconds. ... Asynchronous Transfer Mode (ATM) is a cell relay, packet switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ... IP Telephony, also called Internet telephony, is the technology that makes it possible to have a telephone conversation over the Internet or a dedicated Internet Protocol (IP) network instead of dedicated voice transmission lines. ...

The softswitch generally resides in a building owned by the telephone company called a central office. The central office will have telephone trunks to carry calls to other offices owned by the telephone company and to other telephone companies (aka the Public Switched Telephone Network or PSTN). A telephone company (or telco) provides telecommunications services such as telephony and data communications. ... In the field of telecommunications, a central office or telephone exchange houses equipment that is commonly known as simply a switch, which is a piece of equipment that connects phone calls. ... The public switched telephone network (PSTN) is the concatenation of the worlds public circuit-switched telephone networks, in much the same way that the Internet is the concatenation of the worlds public IP-based packet-switched networks. ...

Looking towards the end users from the switch, the Media Gateway may be connected to several access devices. These access devices can range from small Analog Telephone Adaptors (ATA) which provide just one RJ11 telephone jack to an Integrated Access Device (IAD) or PBX which may provide several hundred telephone connections. Two views of an RJ25 6P6C crimp-on style connector RJ11 is a physical interface often used for terminating telephone wires. ... IAD or Integrated Access Device is a device that consolidates voice, data, Internet, and video services using ATM over T1/E1 lines. ... PBX redirects here. ...

Typically the larger access devices will be located in a building owned by the telephone company near to the customers they serve. Each end user can be connected to the IAD by a simple pair of copper wires.

The medium sized devices and PBXs will typically be used in a business premises and the single line devices would probably be found in residential premises.

In more recent times (i.e., the IP Multimedia Subsystem or IMS), the Softswitch element is represented by the Media Gateway Controller (MGC) element, and the term "Softswitch" is rarely used in the IMS context. A Media Gateway Controller (MGC) is a system used in certain Voice over IP telephony architectures. ...

Feature server as a part of softswitch

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. Call forwarding (or call diverting), in telephony, is a feature on some telephone networks that allows an incoming call to a called party, which would be otherwise unavailable, to be redirected to a mobile telephone or other telephone number where the desired called party is situated. ... Call waiting, in telephony, is a feature on some telephone networks. ... Last Call Return (in North America) or Call Return (in the United Kingdom and Australia) is a telephone feature code offered by telephone service providers to give a called party the time and telephone number of the last received call, and may also offer the facility to place a call...

See also

• Telephone switch
• IP Multimedia Subsystem