Softswitches are the components used in the telecommunications industry for connecting two different phone lines from separate networks or public internet that entirely uses software to run on a general-purpose system.

As the name implies, softswitch uses a software-based solution that runs on standard hardware.

Softswitch is the backbone of VoIP communications.

Instead of using dedicated hardware to control calls like traditional switches, softswitches function in a virtual space.

Softswitch applies to all devices that handle IP-to-IP phone calls.

These are mainly responsible for two main tasks: Terminal Control and Call Control

Terminal control is for detection, authentication of a telephone, and checking the status of whether the telephone is in use or not.

Call control includes signaling, call routing, and call accounting.

Softswitch combines two distinct functional elements:

• Call agent or call feature server for call control, signaling, and routing, and
• A media gateway or access gateway for processing media platforms.

Call Agent:

Call agents are the software switching elements of Softswitches that handle billing, call routing, transferring signals, call service, and other functionalities.

Call agents also manage the functioning of other parts of Softswitch with the connections over the Transfer Control Protocol (TCP) and Internet protocol (IP).

A call agent may also control different media gateways in geographically dispersed areas via an IPN network.

Media Gateway or Access Gateway:

Media gateway refers to those devices that either originate or terminate traditional landline phone calls.

A media gateway might take a call originating from traditional phone lines, and convert it to IP traffic and send it to another device, which terminates the call by reversing the process.

The voice-over IP call then gets converted to circuit-switched digital systems.

To run this process the media gateway uses traditional digital time-division multiplexing (TDM) or analog POTS (Plain old telephone service) protocols.

There are many interfaces involved in it that are used for connecting the media to PSTN networks such as DS1, DS3, and E1 networks.

The call agent may control the functioning of the media gateway by connecting the media streams and interfaces keeping them transparent for the end-users of the phone lines.

These two elements can be co-located on a single piece of hardware or can be located on a separate piece of hardware where one call agent can control one or more gateways.

Softswitches provide the extra software-based functionalities that no other networking device provides such as voice mails, call recording, call routing, billing, etc. and all this happens using the software.