PDF of this tutorialA softswitch, also referred to as a "call agent" or "media gateway controller," is software that provides the call control and signaling for the next-generation network. The softswitch moves the service intelligence out of the switch into a database or application server, connects those databases, and ultimately provides the "brains" or operating system for the next-generation voice network. A softswitch ensures that a call is routed through the network to the proper destination and that features from the existing advanced intelligent network (AIN) such as 1-800 and LNP, as well as new multimedia services, are applied to calls as appropriate. While the softswitch architecture is similar to the AIN databases in an SCP, a softswitch provides more robust functionality and is distinguished by providing control to more than one type of switch—including TDM, ATM, IP, etc.—while today's AIN controls only TDM–based switches. This architecture is inherently more flexible and scalable than the architecture of today's circuit switches.
There is significant debate in the industry about the definition of a softswitch, its role within the network, how it should interface with other gateways and softswitches, and how it should interface with the IP and SS7 networks. At the most basic level, a softswitch must contain call-control features and a signaling interface to the SS7 network. Call control relates to the setup and teardown of calls, including service selection ("which services apply to this call?") and call routing ("where will this call be sent?"). In addition, a softswitch must provide call authentication ("what calls is this line allowed to make?"), authorization, and accounting services by accessing information available in the existing SS7 network. The SS7 signaling interface, which allows the softswitch to communicate with today's SS7 network, is in some cases distributed to a stand-alone hardware system called a signaling gateway. Today's softswitches typically operate on the Sun Solaris operating system and include features such as the following:
- Media independence—to make the software agnostic regarding the switching fabric (ATM, IP, TDM, etc.)
- Interoperability—with multiple vendors' media gateway products, the existing PSTN, and off-the-shelf hardware platforms
- Reliability—to carrier standards (five 9s of reliability)
- Support for multiple signaling and control protocols—including emerging and established standards such as ISUP, BICC, SIP, and MEGACO/H.248
- Scalability—to meet carrier network requirements, supporting thousands of call attempts, also known as busy hour call attempts (BHCA) and simultaneous calls
- Open application programming interfaces (APIs)—or "hooks" into third-party software applications and services
