Internet Telephony And The Three "I's"
BY JEFF LAWRENCE
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
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
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.
RECOGNIZING ISSUES OF SCALE
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.
UNDERSTANDING DIFFERENCES BETWEEN THE NETWORKS
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
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
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
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.
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
ADAPTING TO A CHANGING ENVIRONMENT
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
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
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.
TAKING IN A BROADER VIEW
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
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
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 www.trillium.com.