Next-generation switches must support voice services—not only for IP-and ATM-based networks but also for the time-division multiplexer (TDM)-based PSTN. In addition to call control and resource management, there are other requirements of softswitches and next-generation switches:

Media independence—Softswitches must be agnostic in regards to the network (such as ATM, IP and TDM).

Interoperability—Softswitches must work with other softswitches and media gateways from multiple vendors.

Reliability—Softswitches must be reliable to carrier standards.

Support for multiple signaling and control protocols—Softswitches must support emerging and established standards.

Scalability—Softswitches must meet carrier network requirements, supporting thousands of call attempts, also known as Busy Hour Call Attempts and simultaneous calls.

Open application interfaces—Softswitches must support third-party software applications and services.

Softswitch architecture provides two major advantages over current PSTN switch technologies. The first is openness between subelements of a next-generation switch. This openness promotes the ability to mix best-of-breed components, which gives service providers greater flexibility and a clear growth path. A service provider can buy a media gateway from Vendor A, a softswitch/media gateway controller from Vendor B, a signaling gateway from Vendor C and an application server from Vendor D.

The second major advantage of softswitches is that they give service providers added flexibility in providing new services. A service provider could develop telephony services that could be implemented on the application server. They do not have to depend solely on a switch provider for a critical service, as is the case with traditional PSTN switches.

软交换实现语音/IP服务

软交换的要求

下一代的交换机必须支持语音服务，不仅是在基于IP和ATM的网络，而且还要在基于时分多路（TDM）的PSTN（即传统的电路交换公共网—译注）。除了呼叫控制和资源管理外，软交换和下一代交换机还有其他要求：

媒体独立性——就网络而言，软交换不必知道是何种网络（例如是ATM、IP还是TDM）。

互用性——软交换必须能与多家供应商的其他软交换和媒体网关一起工作。

可靠性——软交换必须对运营商的标准是可靠的。

支持多信令和控制协议——软交换必须支持形成中的和已有的标准。

可伸缩性——软交换必须满足运营商的网络要求，能支持数以千计的呼叫企图，也称为高峰期呼叫企图和同时呼叫。

开放的应用接口——软交换必须支持第三方的应用软件和服务。

软交换的体系结构比起目前的PSTN交换技术有两个主要优点。首先是在下一代交换机子部件之间的开放性。这种开放性促进了将最好的部件结合起来的能力，这给服务供应商提供了更大的灵活性和清晰的成长道路。服务供应商可以从A厂商购买媒体网关，从B厂商购买软交换/媒体网关控制器，从C厂商购买信令网关和从D厂商购买应用服务器。

软交换的第二个主要优点是，在服务供应商提供新的服务时给予其更多的灵活性。服务供应商能够开发在应用服务器上实现的电话服务。他们不再为一个重要的服务而不得不依靠一个单独的交换机供应商，如同在传统的PSTN交换机上那样。