A switch is normally a hard thing, on or off, but today's switches are increasingly taking a soft approach.

Wireless penetration, already strong with more than 1.2 billion subscribers, is expected to increase 61% to 1.7 billion subscribers by 2006, according to Motorola research. Wireless usage is displacing wireline at a rate that will soon make wireless the dominant medium for worldwide communication. In conjunction with this rapid growth, a vast number of communication options have become available to end users, including e-mail, Short Message Service (SMS), Multimedia Messaging Service (MMS), and Push-To-Talk (PTT).

For operators, this translates into significant growth in the global subscriber base and demand for both wireless voice and data services that will, in turn, provide the opportunity for greater revenue and greater market share. In addition, operators will have the ability to offer the innovative and differentiating services that a growing customer base will expect.

With these opportunities also come some challenges - such as how a carrier can provide flexible, common wireless platforms that support multiple network generations (2G, 2.5G, 3G, and 4G) as well as multiple access technologies (i.e., CDMA, GSM/UMTS, and WLAN). This article explores the many benefits of moving from circuit switch-based platforms to softswitch-based platforms for current and future deployments.

Many landline/enterprise operators are deploying softswitches to deliver serving features and functionality, and are taking advantage of trunk pooling to significantly reduce tandem costs (see Figure 1).

Likewise, wireless operators are also validating this technology as a more cost-effective and flexible solution for their network needs. During this inflection point in the industry, an increasing number of operators will begin deploying softswitches solely on the merits of the business case. The adoption of digital circuit switches was primarily intended to provide better services and features for voice traffic, and to accommodate some low-speed data. However, in the past few years the paradigm has changed dramatically. Although current networks were designed to optimize voice traffic, the traffic pattern has changed to a mix of voice, data, and most recently, multimedia traffic, resulting in inefficient use of network resources. Clearly, the need exists to deliver network convergence and enhanced applications to enrich the end-user experience.

Traditional Switching Technology
Stated in the simplest of terms, the job of a telephone switch is to connect two bearer paths. In a circuit-based switch, pulse code modulation (PCM) - encoded voice traffic arrives on a time division multiplexing (TDM) circuit, and is switched onto another TDM circuit. Each circuit is a timeslot of a trunk.

Switch-matrix hardware is specialized, and has to be designed to accommodate the number of circuits that a mobility switch is intended to process. The result of this is that traditional switches are designed for market sweet spots and do not gracefully scale upward or downward. Because of the proprietary nature of traditional switches, new features are typically delivered by vertically integrating new functionality into additional custom-built components. To the operator, this means a longer time to bring new, revenue-generating features to market at a higher OpEx and CapEx.

In addition, traditional circuits were designed for voice and are not well optimized for multimedia content. IP networks have proven to be an effective delivery mechanism of multimedia traffic. Softswitch-based platforms support not only TDM, but also IP/ATM transport interfaces, and hence are more suitable to deliver voice, data, and multimedia applications.

Defining the Softswitch
In the softswitch platform, the call control, media gateway, protocol support, signaling, and application layer logic have been separated into an open, standard, computing platform. Superior call-processing performance is achieved by distributing call setup signaling requests across multiple instances of the call-control processes allocated to distributed CPU resources. New feature-interaction logic and new protocol support can be added with no impact to signaling or routing modules.

Services are provisioned on key server elements of the network, based on open industry standards, enabling services to be propagated across physical elements of the network. The established industry standards that drove Internet and e-commerce will allow carriers to create new services or bundle with existing ones. New customer-critical services and features can now be added in significantly less time than is required for traditional legacy switches.

Advantages of the Softswitch
While traditional switching technology has practical sizing limits, the separation of call control and bearer enables softswitches to provide scalability from smaller to larger networks. In addition, softswitch technology allows for geographic distribution by separating call control and bearer traffic as required. This eliminates backhaul costs in areas where there is a large proportion of local traffic.

While circuit switches are typically single purpose as they relate to access technologies, softswitches support multiple protocols. By doing so, they provide operators with the flexibility to take advantage of different access technologies for different types of services/environments, while using the same switching infrastructure, same common billing generation point, and same operational interface.

Additional advantages include: