Just what is a softswitch?

These server-based devices manage phone calls as they come in from packet access links and clear a path for them across the packet network to the destination phones.

But because most phones are still connected via the traditional public phone network, these softswitches also must be able to complete calls across circuit-switched networks. To do that, they control other network elements including media gateways and signaling gateways. Because of this function, softswitches are also referred to as media gateway controllers.

A media gateway translates traffic from, for instance, an ATM access link, to time-division multiplexer or IP that is used as the backbone of the carrier network. A signaling gateway mediates between the signaling used by access devices and signaling used across the service provider network. With a traditional phone network, this is called Signaling System 7.

The definition of softswitches varies. The International Softswitch Consortium limits the term softswitch to the media gateway controller. Some vendors include the media gateway or signaling gateway, too, as part of the softswitch itself.

To set up phone services, softswitches must tap into databases and application servers that define the services customers get. Because they do this via standard API, vendors other than the ones that make the softswitches can write the service programs.

Softswitch proponents tout this as an advantage because it means more providers can write these programs, encouraging competition that will reduce cost and promote innovation. Traditional circuit-switched voice switches include all the functions of a softswitch plus the service applications and databases, much of which is based on proprietary software. So service providers are locked in to one vendor.

Softswitches are also less expensive than traditional voice switches and let service providers migrate away from maintaining a separate network just for voice.