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Special Focus
March 2001


Softswitches And The Future Of Voice Networking


The convergence of voice and data is creating a host of new revenue opportunities for service providers. Because data traffic is growing much faster than telephone traffic, there has been considerable interest in transporting voice over data networks. The ability to combine voice and data on a single network represents a huge cost savings for service providers who must currently support separate voice and data networks. As a result, service providers are reevaluating the way they do business. In order to succeed, they must respond to the changes in the telecommunications landscape by providing differentiated services such as Internet Offload, Tandem and access services, and VoIP.

IP Is The Major Driver For Innovation
VoIP, the ability to make telephone calls and to send facsimiles over IP-based data networks with a suitable level of quality of service (QoS), has become especially attractive to service providers who want to provide voice and data services over a single network, since most networking growth is IP-based. In fact, toll-quality voice over IP has now become one of the key steps leading to the convergence of voice and data communications. Adding voice to packet networks requires an understanding of how to deal with system level challenges such as signaling, interoperability, packet loss, delay, density, scalability, and reliability.

But the value in deploying VoIP is that it is the right infrastructure and the critical first step for service providers to enable revenue generating enhanced IP services. VoIP involves much more than simply adding compression functions to an existing IP network. By standardizing on IP as the service layer, voice becomes just another application on top of the infrastructure. This separation of application and transport will unleash waves of service innovation unrealized up to now. One of the key technologies enabling this separation is the softswitch.

The Value Of Softswitches
Softswitches are a class of equipment that uses software intelligence to allow carriers to integrate voice services running on Internet Protocol (IP) networks across existing Time-Division Multiplexed (TDM) and Asynchronous Transfer Mode (ATM) telecommunications networks. Open service creation and delivery platforms, softswitches allow providers to simply -- and cost-effectively -- integrate converged voice and multimedia services. Their primary value is that they allow service providers to quickly and inexpensively roll out new services without having to involve switch vendors in the process. That is why softswitches create such promising opportunities for service providers to quickly ramp up their Internet revenues.

But picking the right softswitch is the tricky part. There simply is no agreed to definition for a softswitch, but there is hope. Thanks to the efforts of the International Softswitch Consortium, there seems to be a developing consensus around the following definition of a softswitch:

  • Interoperability and support for an open architecture;
  • Scalability and bulletproof reliability; and
  • Regulatory compliance and deployability.

Interoperability And Open Architectures
The important thing to look for when assessing the openness of a softswitch is not necessarily to get bogged down in spec sheet details, such as whether a product supports 1-800 features or a specific service such as local number portability (LNP). It is as important to look at the design to see whether it is open and extensible so that it will support not only the current crop of revenue generating, value-added services, but also new services that have not even been thought of yet. How can you tell? Look for support for legacy and next-generation interfaces. A softswitch needs to provide interoperability with other network components through standard signaling protocols such as SS7 ISUP, TCAP, SIP, SIP T, MGCP, and H.323. Utilizing these standard protocols, a softswitch can provide multiple interworking solutions, including:

  • Switching voice traffic between the PSTN and data networks (SS7, MGCP, H.323);
  • Interworking with other softswitches and application servers (SIP, SIP T);
  • Enable interoperability between legacy and next-generation VoIP gateways and endpoints (MGCP, H.323, SIP); and
  • Provide IP-based services seamlessly across voice and data networks (SS7, SIP, MGCP).

These protocols will be the basis for easy and quick deployment of new value-added services, which will include the "killer applications" that will significantly enhance the revenue streams of service providers.

Scalability And Bulletproof Reliability
It does not matter how much money the service provider can make from these value-added bells and whistles if the softswitch itself does not scale to supporting millions of subscribers, or is not reliable at the levels of the PSTN. What is needed is a platform that delivers "five-nines" levels of uptime; 99.9 percent will not do. One approach to ensuring reliability is to run the softswitch software on highly redundant, high-end servers. The snag is that these servers start at around $400,000 and are not scalable. Worse, expensive hardware only addresses half the problem.

To ensure maximum uptime, the software that runs on the server also must be protected. A promising solution now gaining ground is to use clustering software that can spread softswitch intelligence over multiple servers. This approach increases the reliability of the network, since clusters are less vulnerable to software bugs. Further, load balancing features inherent in clustering applications also improve performance by allowing processing tasks to be spread over multiple servers. Clustering also cuts down on capital outlay because it allows less expensive server hardware to be installed for between $30,000 and $40,000.

Regulatory Compliance And Deployability
Having an open, scalable, reliable softswitch does not indicate that the product is deployable in a production networks. Signaling certification (e.g., via Telcordia), number translation that meets the needs of service providers, support for FCC regulatory issues (CALEA, LNP, and E911) and operator/directory assistance are issues that are not evaporating with the adoption of voice as an IP application. As such, it is critical to look for the support of these functions, and also the field deployments that have "shaken out" the early problems that any new product encounters when it is introduced to live traffic.

Just A Part Of The Equation
When looking at a service, service providers typically think in terms of end-to-end solutions. Therefore it is critical to take a look at two other important components in terms of delivering the new multi-service IP network: The mediation function between packet and circuit and the underlying IP infrastructure.

First let's look at the mediation equipment (commonly referred to as media gateways) that mediates between circuit and packet. These gateways need to support cutting edge DSP technology to provide high density and unsurpassed scalability, best-in-class voice processing (including compression algorithms like G.726 and G.729/A), and especially quality of service (QoS) integration with the underlying IP infrastructure for edge-to-edge toll-quality voice. Integration of customer premise equipment QoS is then critical to provide end-to-end toll-quality voice, which is mandatory for voice service on any network. However, QoS is currently only a discussion to have under "favorable conditions," which typically do not exist in production networks.

As such, the underlying IP infrastructure needs to be upgraded to support wirespeed interfaces, as well as wirespeed classification and acting on that classification. These functions are mandatory in products built to support the IP infrastructure that can carry voice traffic reliably and consistently. But this new multiservice IP network needs also to support "traditional data" services at the edge, such as frame relay, ATM, and circuit-based point-to-point transport. Optical equipment, while cost effective and feature rich, must maintain support for the legacy network close to the network's edges in order to protect the investment in the legacy network. Users will still be connecting to the PSTN using modems where appropriate or cost effective, even as broadband access is deployed and adopted.

Private line services, including leased data lines and voice tie-lines will continue to be revenue generators for carriers, but they too will be relegated to the application space. Private voice and data applications can use IP VPNs as a replacement for private facilities. Interoffice IP networks, today commonly frame relay-based, are also important services and frame relay mediation is a necessary function of leading edge router technology.

In Summary
There is no doubt the softswitch category requires a lot of thought and consideration. But it is also increasingly clear that service providers cannot afford to ignore this product class. Creating your own softswitch definition and matching it to the available products is the fastest way for a service provider to identify the product that will let them offer new and varied voice service quickly and easily. But it is just as critical to look at the edge-to-edge network solution including the IP transport layer and the mediation layer. This new IP network must become multiservice, allowing multimedia applications to generate revenue in addition to transport access charges. Remote Access Service (RAS), Voice Service, ASP, wireless multimedia, and other emerging services are the future revenue generators for IP networks. Only by delivering best-in-class offerings in all these segments will service providers survive in this market. c

Pedro Colaco is director of product marketing for Unisphere Networks' Voice Division. Unisphere assesses, develops, and markets advanced technology by providing the technical, business, and financing resources that transform prototype stage innovations into products that compete successfully in the global marketplace. Please visit their Web site at

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