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:

Supports multi-interfaces/protocols

Softswitch Applications
To further illustrate the advantages that softswitches provide, it's important to also look at the applications they can deliver. Three critical examples include:
1.  Providing a Gateway Mobile Switching Center (GMSC): In today's network, each MSC has a physical connection to all other network elements using trunks. This approach is not only highly unmanageable in large networks as the networks expand and grow, it is also cost prohibitive as the transport cost increases with the meshed trunks. Operators can not only reduce trunk costs, but can also improve resource utilization of the deployed switches by introducing a softswitch as a Gateway MSC.
2.  Providing a full-featured Mobility Switch (Serving MSC): The Serving MSC fits in an operator's network to provide the call setup/teardown; mobility management; billing; and operations, administration, maintenance, provisioning (OAMP).
3.  Providing a distributed Switch (Gateway/Serving MSC): Distributed switching can significantly reduce the backhaul cost because the bearer traffic stays local for local calls and does not require routing the call to the central location and then back to the local PSTN for termination. The distributed switching allows operators to offload long-distance tariffs by using their own IP packet transport network, and enables logical call termination when a roaming subscriber receives a call placed from the visited area.

Future-Proofing Today's Wireless Networks
Eventually, we believe there will exist a world where circuit-based interconnection to communications networks is no longer the main interconnection method. It is foreseeable that the interface between MSCs and Radio Access Networks (RAN) will become packetized due to inherent benefits in IP technology, such as life-cycle cost reduction and new innovative features that can be rapidly brought to market.

Softswitches are available today and, based on our extensive field work with global network operators, Motorola believes they provide significant advantages as alternatives to traditional circuitbased switches. Softswitches expand the capacity of existing networks, can decrease capital and operational costs, and provide investment protection as the industry evolves to an all-IP future - future proofing today's networks.

By adopting new-generation softswitch platforms, operators have the ability to succeed and realize capabilities like the ability to support 2G, 3G, and 4G networks simultaneously. Tremendous market opportunities already exist, particularly in emerging markets and among early adopters in mature markets where operators find them an attractive option for upgrading network capacity.

To succeed and do so profitably, operators will need to make the right infrastructure choices in a market where services must be launched quickly, multiple protocols supported simultaneously, and costs vigorously contained. Operators that adopt new-generation platforms will have a competitive edge in delivering wireless services.

Published Nov. 25, 2003 — Reads 9,405
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About Eduardo Conrado
Eduardo Conrado joined Motorola in 1991 and is senior director of systems marketing and portfolio management in the global marketing organization of Motorola's Global Telecom Solutions Sector.