User:AlephGamma/Call Agent

=Softswitch= A programmable network switch that can process the signaling for all types of packet protocols. Also known as a "media gateway controller," "call agent" or "call server," such devices are used by carriers that support converged communications services by integrating SS7 telephone signaling with packet networks. Using network processors at its core, softswitches can support IP, DSL, ATM and frame relay in the same unit.

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 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. Well-known manufacturers of Softswitches include Nokia, Veraz Networks, Ericsson, Huawei, Lucent, MetaSwitch, Motorola, Nortel, Tropico, Marconi, Siemens, Sonus, Alcatel, Santera (Tekelec), Avaya, Cisco Systems, PortaOne, Cirpack, ZTE and Iskratel.

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.

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.

So where does this switch sit in the network? The softswitch generally resides in a building owned by the telephone company called a central office. The central office will have one or more 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).

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.

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.

It Should Be Able To
According to the International Softswitch Consortium, a softswitch should be able to (1) control connection services for a media gateway and/or native IP endpoints, (2) select processes that can be applied to a call, (3) provide routing for a call within the network based on signaling and customer database information, (4) transfer control of the call to another network element, and (5) interface to and support management functions such as provisioning, fault, billing, etc.

Software Makes It Flexible
The switching technology in a softswitch is in software (hence its name) rather than in the hardware as with traditional switching center technology. This software programmability allows it to support existing and future IP telephony protocols (H.323, SIP, MEGACO, etc.). See IP telephony. See also Soft-Switch.

External References
Techweb - Softswitch