BY JEFF LAWRENCE

Internet telephony will only succeed in the marketplace if the Internet and the PSTN appear as a seamless network to users. Users expect to be able to access and use a broad range of services regardless of the underlying infrastructure. However, integrating the disparate infrastructures and services of the Internet and PSTN will present a number of challenges. In addition, the development of new telecommunications services derived from the integration of the Internet and the PSTN is complex, time consuming, and costly. These new telecommunications services must not adversely affect network reliability, network integrity, or personal privacy, nor should they generate undesirable interactions with other telecommunications services within the same network.

THE CONFUSION
A number of phrases, including the "intelligent network" and "computer telephony" describe the various models used to provide these services. Distinctions arise from the physical location of the equipment, and the identity of the entity using and managing the intelligence. The concept of the "intelligent network" came out of the desire of service and network providers to separate the service intelligence from the switching intelligence. Having accomplished this separation, service and network providers could simplify the development of various services, such as call charging, local number portability, and CLASS services, and develop their services independently of any particular vendor equipment. The separation of service intelligence and switching intelligence also provided the flexibility to support the interconnection of differing networks and the adaptability to address changing user and network demands.

The concept of the intelligent network existed long before the concept of Internet telephony, i.e., voice over IP (VoIP). Unfortunately, the label Internet telephony creates some confusion because it is a mixed metaphor that combines the concepts of the Internet as an "infrastructure" and telephony as a "service." It is more accurate to describe Internet telephony as "telephony service over the Internet." An equivalent description for existing telephony services running over the circuit-switched and SS7 networks would be "telephony service over the PSTN."

DISTRIBUTING AND INTEGRATING INTELLIGENCE
The intelligence that supports existing and future services will be distributed throughout the Internet and PSTN infrastructures. In some cases, intelligence will be located on the user's premises, and, in other cases, it will reside in the access and core parts of the network. Today, the Internet and the PSTN are effectively two separate infrastructures joined by gateways. The intelligence controlling the Internet (in the form of name servers, gatekeepers, and call agents) and the intelligence controlling the PSTN (in the form of service control platforms and location registers) are independent of each other. In the future, these separate infrastructures will become more tightly integrated until they evolve into a single infrastructure, and the term "distributed network intelligence" will more accurately reflect the architecture of the network.

Distributed network intelligence is dependent on the development and deployment of a number of enabling elements that consist of information repositories, applications to manipulate and transform information, and processing platforms -- where applications and information are brought together to interact. Information repositories and processing platforms are connected by the other elements of the access and transmission networks. The successful interconnection and coordination of these various elements depends on the SS7, ATM, H.323, SIP, MGCP, and signaling and data transfer protocols. These protocols are different from each other and reflect the differences of the network architectures and infrastructures they are designed to support. For example, the SS7 protocol was originally developed to provide out-of-band signaling for voice services over the circuit-switched network. Changes to the SS7 protocols over the last few years have added support for virtual connections and data services. The H.323, SIP, and MGCP protocols have varying levels of complexity, but generally have been developed to support multimedia services such as voice, data, audio, and video over IP networks.

ORGANIZING INTELLIGENCE
Within the PSTN, the information repositories and applications co-reside on service platforms (consisting of service control points, intelligent peripherals, and adjunct processors) for intelligent network services and on-location registers for wireless access services. These platforms and location registers typically communicate with each other and the switching elements within the access and core networks by the SS7 protocols. A combination of market demands, competitive pressures, and regulatory requirements have driven the development of PSTN services including: Mobility, voice mail, dynamic call routing, local number portability, line information database, various call charging services, various call management services, and network call center services.

Within the Internet, information repositories and applications are organized differently. Name servers provide the information needed to route connections between clients and servers. RADIUS servers provide security services for virtual private networking over the Internet. Gatekeepers and gateways are relatively new architectural additions that enable the interconnection of Internet devices with the PSTN. Gateways provide the translation services between the signaling and media streams of the Internet and PSTN, and gatekeepers assist in the routing of connections to the appropriate gateway. Call agents are part of the MGCP architecture, and potentially provide the starting point of a new platform that can be used to unify Internet and PSTN services. There don't appear to be equivalent architectural developments for service platforms that reside in the PSTN infrastructure.

Call Agent Conduits
Call agents reside on the Internet and can terminate H.323, SIP, and MGCP connections from the Internet, as well as SS7 connections from the PSTN. SS7 connections (either TCAP or ISUP) from the PSTN are directed to the call agent via IP from the gateway. TCAP is used in the PSTN and supports transactions among applications or databases residing on different service platforms. TCAP is currently used by applications to support the lookup of routing and other information. ISUP manages basic call setup and teardown, and also supports other supplementary services. A number of integration issues arise at the interface between the ISUP, TCAP, H.323, SIP, and MGCP protocols. In the world of IP, H.323, SIP, and MGCP, there tend to be few protocol variations. However, in the world of TCAP, and especially in the world of ISUP, there are literally dozens of protocol variations that are different enough from each other to be incompatible. In addition, ISUP is still limited in its ability to transparently carry information among connected H.323 networks. This limitation generates numerous interoperability issues since proprietary solutions are required to tunnel through the PSTN to connect H.323 networks.

The location of call agents in the combined Internet-PSTN infrastructure allows them to easily access databases used in the PSTN, as well as name servers used for the Internet. Call agents are also conveniently positioned to bind various voice, data, and other connections into a single coherent session from the end-user perspective. This binding, combined with the ability to manage media-stream conversions among the different network infrastructures, points to the likelihood that call agents will become the primary coordinating "intelligence" between the Internet and PSTN infrastructures. Call agent applications will run on the call agent platform and access information repositories either co-resident with the applications or distributed elsewhere in the network.

PSTN services have very well-defined behavioral, information, and business models. Internet services are relatively immature, and in many cases are still in their early formative stages. The integration of Internet-based services -- such as Web browsing, e-mail, e-commerce, and e-collaboration -- with voice and other services provided by the PSTN, is creating a number of opportunities and challenges. New services such as "click-to-dial," user-based service provisioning and management, Web call centers, and others will evolve from the integration of the Internet and PSTN. Resolving the behavioral and procedural differences between the Internet and PSTN is relatively simple compared to the development of provisioning, revenue, and settlement models for this new environment. These models must be normalized among different service providers and network operators to ensure device portability, number portability, service interoperability, and rational billing and customer care models from the end-user perspective.

THE SOLUTION
A number of organizations are involved in developing procedural and service models to integrate the PSTN and Internet network infrastructures. In addition to the International Telecommunications Union (ITU, www.itu.org), Internet Engineering Task Force (IETF, www.ietf.org), and European Telecommunications Standards Institute (ETSI, www.etsi.org), there are currently three industry forums focused on addressing various aspects of integrating the Internet with the PSTN infrastructure. These include the recently formed SoftSwitch Consortium (www.softswitch.org), which focuses on IP-to-PSTN integration issues, the Multiservice Switching Forum (www.msforum.org), which focuses on ATM-to-PSTN integration issues, and the Intelligent Network Forum (www.inf.org), which has been working for some time on developing procedural and service models for IN-to-IP integration.

The concept of distributed network intelligence will provide a powerful foundation upon which the next-generation network can be built. It will supplant the intelligent network and computer telephony, and provide the framework upon which information, applications, and the means to bring them together can create services needed and valued by end users, service providers, and network providers. The continuing challenge of service and network providers will be to maintain and enhance existing services while ensuring sufficient intelligence, flexibility, application portability, and interoperability to support new services evolving from the continued integration of the telephony, Internet, wireless, and cable infrastructures.

Jeff Lawrence is President & CEO of Trillium Digital Systems, Inc. Trillium provides solutions for telephony, intelligent networks, the Internet, wireless, and broadband networks. Solutions consist of communications software, support and value-added software integration, customization, and consulting services for SS7, ATM, IP, wireless, ISDN, frame relay, V5, and X.25/X.75 technologies. Trillium also offers complementary solutions for fault-tolerance/high-availability, protocol interworking, Java, and Software on Silicon. For more information, visit Trillium's Web site at www.trillium.com.