A softswitch (''software switch'') is a call-switching node in a

telecommunications network A telecommunications network is a group of nodes interconnected by telecommunications links that are used to exchange messages between the nodes. The links may use a variety of technologies based on the methodologies of circuit switching, mes ...

, based not on the specialized switching hardware of the traditional

telephone exchange telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...

, but implemented in software running on a general-purpose computing platform. Like its traditional counterparts it connects

telephone call A telephone call is a connection over a telephone network between the called party and the calling party. First telephone call The first telephone call was made on March 10, 1876, by Alexander Graham Bell. Bell demonstrated his ability to "ta ...

s between subscribers or other switching systems across a telecommunication network. Often a softswitch is implemented to switch calls using

voice over IP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...

(VoIP) technologies, but hybrid systems exist. Although the term ''softswitch'' technically refers to any such device, it is conventionally applied to a device that handles IP-to-

IP phone A VoIP phone or IP phone uses voice over IP technologies for placing and transmitting telephone calls over an IP network, such as the Internet. This is in contrast to a standard phone which uses the traditional public switched telephone network ...

calls, while the phrase '' access server'' or "media gateway" is used to refer to devices that either originate or terminate traditional

land line A landline (land line, land-line, main line, home phone, fixed-line, and wireline) is a telephone connection that uses metal wires or optical fiber telephone line for transmission, as distinguished from a mobile cellular network, which uses ...

phone calls. In practice, such devices can often do both. An access server might take a mobile call or a call originating from a traditional telephone line, convert it to IP traffic, then send it over an IP network to another such device, which terminates the call by reversing the process and converting the

call to circuit-switched digital systems using traditional digital

time-division multiplexing Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fracti ...

(TDM) or analog POTS protocols. The call agents are the software switching elements of the softswitch. Other components handle functions for billing, directory services, network signaling. The network elements that convert voice streams between VoIP links and traditional media technologies, such as analog telephone lines, pair-gain devices, carrier systems, are called media gateways. A call agent may control many different media gateways in geographically dispersed areas via an IP network. The softswitch generally resides in a building owned by a

telephone company A telephone company, also known as a telco, telephone service provider, or telecommunications operator, is a kind of communications service provider (CSP), more precisely a telecommunications service provider (TSP), that provides telecommunicat ...

, called a

or central office, or in a

data center A data center (American English) or data centre (British English)See spelling differences. is a building, a dedicated space within a building, or a group of buildings used to house computer systems and associated components, such as telecommun ...

. Such locations have high capacity connections to carry telephone calls or digital communication to other switching centers. Access devices to the services of a softswitch range from large media gateways with high port density to integrated access devices (IAD) at office locations, to small analog telephone adaptors (ATA) which provide just one RJ11 telephone jack to a residence. Embedded multimedia terminal adapters (eMTAs) are also built into cable television modems. A softswitch routes telephone calls using the Signalling System No. 7 (SS7) network. SS7 modules may be implemented directly in the softswitch, or accessed from standalone signaling servers. At the turn of the 21st century with

IP Multimedia Subsystem The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem (IMS) is a standardised architectural framework for delivering IP multimedia services. Historically, mobile phones have provided voice call services over a circuit-switched-styl ...

(IMS), the softswitch element is represented by the

media gateway controller The media gateway control protocol architecture is a methodology of providing telecommunication services using decomposed multimedia gateways for transmitting telephone calls between an Internet Protocol network and traditional analog facilities of ...

(MGC) element, while the term ''softswitch'' is rarely used in the IMS context, where it is called an ''access gateway control function'' (AGCF).

Class 4 and Class 5 softswitches

VoIP softswitches are subdivided into Class 4 and Class 5 systems, in analogy to the traditional functions in the

public switched telephone network The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telep ...

. Softswitches used for transit VoIP traffic between carriers are usually called Class 4 softswitches. Analogous with other

Class 4 telephone switch A class-4, or tandem, telephone switch is a U.S. telephone company central office telephone exchange used to interconnect local exchange carrier offices for long distance communications in the public switched telephone network. A class-4 switc ...

es, the main function of the Class 4 softswitch is the routing of large volumes of long-distance VoIP calls. The most important characteristics of Class 4 softswitch are protocol support and conversion,

transcoding Transcoding is the direct digital-to-digital conversion of one encoding to another, such as for video data files, audio files (e.g., MP3, WAV), or character encoding (e.g., UTF-8, ISO/IEC 8859). This is usually done in cases where a target d ...

, calls per second rate, average time of one call routing, number of concurrent calls. Class 5 softswitches are intended to serve subscribers. Class 5 softswitches are characterized by additional services for end-users and corporate clients such as IP PBX features, call center services, calling card platform, types of authorization, QoS, Business Groups and other features similar to other Class 5 telephone switches.

References

{{Switches Switches Telephone exchanges

Class 4 and Class 5 softswitches

See also

References