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January 1999

Internet Telephony And The Three "I's"


Service providers, carriers, and equipment manufacturers have embraced Internet telephony; indeed, they are counting on its success. It remains, however, for Internet telephony's practitioners - or adherents, at any rate - to overcome a variety of technical, political, and regulatory challenges. Once these challenges are overcome, Internet telephony's success will be possible, even probable, if not assured.

The challenges posed by Internet telephony emerge from the need to obscure, and eventually erase, the boundaries between the Internet and the Public Switched Telephone Network (PSTN). In other words, it will be necessary to accomplish the integration of the Internet and the PSTN, which will be made possible through interoperability and interworking. (These are the three "I's" of Internet telephony - integration, interoperability, and interworking.)

The successful integration of network infrastructures as different as the Internet and the PSTN ultimately depends on the ability of equipment to communicate and exchange information locally (interoperability) and on the ability of the applications and services running in the equipment to communicate and exchange information on an end-to-end basis (interworking). It is important to note that while equipment may interoperate (that is, make a connection and transfer information), the applications and services may still not interwork.

The existing telephony network has established a standard for service that Internet telephony must meet if it is to succeed. Users making a voice call will not want to have to know whether the person they are calling is located on the Internet or on the PSTN. Rather, they will simply want to be able to dial a number, wait a couple of moments, and then hear the phone ringing. This demands that the Internet and the PSTN (two very different infrastructures - one packet-based and the other circuit-based) must be integrated into what appears to be one seamless network. This is much easier said than done.

While the challenges of integration may seem daunting, the rewards of meeting them are considerable. Internet telephony promises to use bandwidth efficiently with compression and packet switching; to integrate infrastructures and services such as voice, Web, e-mail, fax, and video; to lower operational, infrastructure, and access costs for service providers; to generate revenues from new infrastructure and services; and, finally, to lower costs to end users.

The difficulty of solving interoperability and interworking issues varies proportionately to the scale of the network. That is, the difficulty increases as a call moves from an office across an enterprise network and into the public network.

Within The Office
Internet telephony can be deployed within an office environment quickly and easily. In this case, the network equipment is under the control of the enterprise, and there is typically no need to deal with complicated operational, provisioning, and billing issues.

Voice calls within the office can be switched through a shared or switched media Local Area Network (LAN) via a router. Voice calls destined to a user in the public network can be transformed and routed out of a LAN PBX (Private Branch Exchange) to look like a traditional phone call to the PSTN.

The equipment needed to build this type of network can be purchased from a single vendor and, by design, should not have any interoperability or interworking problems. This solution offers very attractive cost savings, since a single wiring infrastructure can be used for the transmission of both voice and data. Furthermore, there is minimum administrative overhead to move and reconfigure phones within the office.

Within The Enterprise
Enterprise networks can interconnect multiple office locations through leased lines or Internet services using IP tunnels. Again, the Internet telephony service is still effectively under the control of the enterprise. Voice calls within the enterprise are made via Internet telephony. And - as in the previous example - voice calls destined to a user in the PSTN can be transformed and routed out of a LAN PBX to look like a traditional phone call to the public network.

In the enterprise, as in the office, solutions use Internet telephony unless calls involve people on the PSTN, in which case it may be necessary to revert to traditional solutions. Interoperability and interworking issues can be easily managed if the terminals and the LAN PBXs are supplied by a single vendor. Things become more complicated, however, if we must accommodate users who are not insulated from the PSTN by LAN PBXs, or users who are directly connected to the Internet.

Across Disparate Networks
The merging of the Internet and PSTN will occur at the gateways and the gatekeepers in the Internet and the service platforms in the PSTN. To the PSTN, the Internet will look like just another user. Initial connections between the Internet and the PSTN will occur via gateways and LAN PBXs supporting ISDN. As the standards for interworking between H.323 and ISUP are defined, Internet-to-PSTN solutions that utilize the SS7 protocol will emerge.

Until general interworking standards are defined, the industry will continue to utilize proprietary solutions that are very dependent on the individual interpretations of equipment manufacturers, service providers, and carriers. These proprietary solutions are only interim in nature, and, over time, will be replaced by more generalized solutions that will allow seamless interoperability and interworking between varying national and international network infrastructures. It should also be noted that service providers and carriers will not allow easy access to their signaling networks unless the equipment connecting to these networks has been thoroughly tested and certified.

The technical and operational differences between the Internet and the PSTN are significant. Indeed, these differences constitute challenges that must be addressed before Internet telephony can have the same widespread presence and level of service as today's PSTN.

The challenges described in this section range from bits and bytes at the protocol level, to policy decisions at the national and international levels. They demonstrate that the expertise of the people involved in the telephony and data worlds must be shared and combined to ensure orderly development and integration of the Internet and PSTN infrastructures.

There are fundamental conceptual differences between the PSTN and Internet on the data, control, and management planes. The PSTN is circuit-based and connection-oriented, and it has a centralized control structure. The Internet is packet-based and connectionless, and it has a minimal control structure.

The mapping of messages and data flows between these two infrastructures is being defined by the International Telecommunication Union (ITU), the European Telecommunications Standards Institute (ETSI), and the Internet Engineering Task Force (IETF). New hybrid management mechanisms are being developed that allow varying levels of control and monitoring by service providers and carriers as well as by the users themselves. These mechanisms are being defined by the service providers, carriers, and equipment manufacturers under Telecommunications Management Network (TMN), Simple Network Management Protocol (SNMP), and Web-based frameworks.

In addition, there are many differences between national and international variations of the "same" protocol. These differences cannot be overlooked and must be considered during the development and deployment of equipment.

There is a wide range of telephony services, including basic calling, call waiting, call forwarding, and conference calling. Providing these and other services across infrastructure boundaries will require coordination, bridging, and translation protocols between gateways, gatekeepers, and service platforms supporting Line Information and other databases. These protocols will work with the TCAP, INAP, and MAP SS7 protocols, Gateway Control Protocols, and H.323.

There are addressing and numbering differences between the PSTN and the Internet. Every phone needs at least a physical address and quite often a logical address. The PSTN uses E.164 addresses as defined by the ITU. The Internet uses IP addresses as defined by the IETF.

E.164 addresses have a geographic-based format, whereas IP addresses follow a very different format. There are several approaches under consideration by the ETSI and the ITU for placing a call from the PSTN to the Internet and vice versa, utilizing the different addressing and numbering schemes.

PSTN calls are typically billed on duration and distance. Internet telephony calls can be billed on the basis of packets. Mapping between these different measurements and establishing settlement rates must occur at the industry forums, on both an abstract basis (in the form of Call Detail Records), as well as on a policy basis (between service providers, carriers, and regulatory organizations).

Additional complications arise because of the non-deterministic nature of the Internet. It is likely that many users will require Service Level Agreements with their Internet providers as well as mechanisms to monitor that the guaranteed service levels are being met. If these service levels are not met, it may affect the ability of service providers to bill the user. New hybrid billing mechanisms are under development that allow the monitoring of billing information by users from the Web on a real-time basis.

Quality Of Service
Guaranteeing a level of Quality of Service (QoS), including throughput, delay, and jitter for a voice call, is straightforward on the PSTN but much more complicated on the Internet. Service providers and carriers must sign Memorandums of Understanding to ensure that there is an appropriate QoS mapping for services that cross infrastructure boundaries of similar or different technologies. Policies must also be established regarding call management if the required QoS cannot be provided.

Location Management
Wireless and mobile services are enabled by a number of different elements such as switching centers, location registers, and base stations located within the network. Today, the wireless and mobile networks primarily have a voice focus. Future networks will have a data focus because mobile and wireless networks fully support the integration of voice and data. In these networks, Line Information and other databases will need to support IP addressing and routing mechanisms for location management and handoff.

There are many operational differences between the centralized control structure of the PSTN and the minimal control structure of the Internet. This will have a significant impact on Operational Support Systems (OSSs) and Network Management Systems (NMSs).

The PSTN typically has relied on closed proprietary OSSs and NMSs. The Internet does not have such a legacy nor does the Internet even need such systems. New hybrid management solutions are being developed that allow varying levels of control and monitoring by service providers and carriers as well as by the users themselves. These solutions are based on TMN, SNMP, and Web-based concepts using a combination of agents and network managers.

To date, technologies have interworked because the scale of an Internet telephony call has been limited. As the scale expands, making an Internet telephony call will be more difficult.

Solutions are evolving quickly. The market and equipment manufacturers are ahead of the standards organizations and, to a lesser extent, industry forums. The ITU, the IETF, the ETSI, the VON (Voice Over Net) group, and the IMTC (International Multimedia Teleconferencing Consortium) have all been working on various technical aspects of integrating the Internet and the PSTN. Others are working on the policy and regulatory aspects.

Even as we rush toward new solutions, there is a feeling in the industry that the days of H.323 - a popular Internet telephony protocol standard - are numbered. Its initial success has been in terminal, gateway, and gatekeeper equipment. H.323 is a full-featured protocol with a high degree of complexity and a large code size.

Many people within the industry feel that in the next few years the term Session Initiation Protocol (SIP) and newly defined gateway control protocols such as the Multimedia Gateway Control Protocol will become the dominant forces for Internet telephony. SIP provides a less complex solution with a correspondingly smaller code size that will be more attractive for future terminal designs. Because of its widespread usage and relative maturity, H.323 will continue to play an important role for some time until these new protocols are refined, integrated into products, and deployed.

In the future, as now, it will be very important to pay attention to the changing environment and to stay flexible. The technical solutions clearly will continue to evolve over the next few years as service providers, carriers, equipment manufacturers, and standards organizations work toward the integration of the PSTN and the Internet infrastructures. Equipment may become obsolete even before it is installed. It is absolutely critical to ensure that the products and services deployed can adapt to changing technical requirements and can be easily upgraded in the field. Much will change before the many technical and regulatory issues are settled.

We've focused on Internet telephony within this article, but, interestingly, these issues are a microcosm of the far broader issues that service providers and carriers will have to address as they attempt to find ways to integrate other disparate technologies and protocols.

Existing network infrastructures cannot be discarded overnight. Solutions must be developed that allow individuals, businesses, and organizations to move at their own pace from existing to new infrastructures. The types of issues encountered by Internet-to-PSTN integration also hold true for the integration of other network infrastructures, including IS-41-to-GSM wireless, GPRS-to-3G wireless, frame relay-to-Internet, and broadband-to-narrowband.

One of the truly great success stories of the telephone network has been its ability to introduce new services and technologies with minimal impact on the users and their expectations. Continuing of this tradition makes it imperative that the industry use a multi-faceted approach to quickly specify and implement unambiguous interworking solutions and provide coordinated industry-wide interoperability and interworking test events that not only involve equipment manufacturers but also service providers and carriers. Failure to do so will result in many missed opportunities and may squander what are some of the most significant legacies of today's telephone network: ubiquitous and easy-to-use services that cross various technologies seamlessly.

Jeff Lawrence is president and CEO of Trillium Digital Systems, Inc., a leading provider of communications software solutions for computer and communications equipment manufacturers. Trillium develops, licenses, and supports standards-based communications software solutions for SS7, ATM, ISDN, frame relay, V5, IP, and X.25/X.75 technologies. For more information, visit the company's Web site at

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