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Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
Applications and Benefits of VoIP . . . . . . . . . . . .
4
IP Network Support for Voice . . . . . . . . . . . . . .
14
Software Support for VoIP . . . . . . . . . . . . . . . . .
19
Implementing VoIP in Systems. . . . . . . . . . . . . .
26
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
CASE STUDY: How Entrata’s Partnership
With Telogy Networks Filled a Niche
in the Voice over Packet Market . . . . . . . . . .
31
Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . .
34
About the Editor…
Jerry Ryan is the Vice President of Editorial Development for the Technology
Guides on Communications and Networking. Mr. Ryan is also a principal at
ATG. Mr. Ryan has developed and taught many courses in network analysis
and design for carriers, government agencies and private industry. He has pro-
vided consulting support in the area of WAN and LAN network design, negoti-
ation with carriers for contract pricing and services, technology acquisition, cus-
tomized software development for network administration, billing and auditing
of telecommunication expenses, project management, and RFP generation. He
was the president and founder of Connections Telecommunications, Inc., a
Massachusetts based company specializing in consulting, education, and soft-
ware tools which address network design and billing issues. Mr. Ryan is a mem-
ber of the Networld+Interop Program Committee. He holds a B.S. degree in
electrical engineering.
This book is the property of The Applied Technologies Group, Inc. and is
made available upon these terms and conditions. The Applied Technologies
Group reserves all rights herein. Reproduction in whole or in part of this
book is only permitted with the written consent of The Applied Tech-
nologies Group. This report shall be treated at all times as a proprietary
document for internal use only. This book may not be duplicated in any way,
except in the form of brief excerpts or quotations for the purpose of review.
In addition, the information contained herein may not be duplicated in
other books, databases or any other medium. Making copies of this book, or
any portion for any purpose other than your own, is a violation of United
States Copyright Laws. The information contained in this report is believed
to be reliable but cannot be guaranteed to be complete or correct.
Copyright © 1998 by The Applied Technologies Group, Inc., One Apple
Hill, Suite 216, Natick, MA 01760, Tel: (508) 651-1155, Fax: (508) 651-1171
E-mail: info@ techguide.com Web Site: http://www.techguide.com
Communicating via packet data networks such as IP, ATM,
and Frame Relay has become a preferred strategy for both corpo-
rate and public network planners. Experts are predicting that data
traffic will soon exceed telephone traffic, if it hasn’t already. At
the same time, more and more companies are seeing the value of
transporting voice over IP networks to reduce telephone and
facsimile costs and to set the stage for advanced multimedia appli-
cations. Providing high quality telephony over IP networks is one
of the key steps in the convergence of voice, fax, video, and data
communications services. Voice over IP has now been proven
feasible; the race is on to adopt standards, design terminals and
gateways, and begin the roll-out of services on a global scale.
Needless to say, the technical difficulties of transporting voice and
the complexities of building commercial products are challenges
many companies are facing today. Adding voice to packet networks
requires an understanding of how to deal with system level chal-
lenges such as interoperability, packet loss, delay, density, scala-
bility, and reliability. The Internet and the corporate Intranet
must soon be voice-enabled if they are to make the vision of
“one-stop networking” a reality. This Technology Guide examines
recent advances in the infrastructures, equipment, and embedded
systems that are needed to successfully enable VoIP and discusses
the major issues currently facing product developers. The types of
applications that will benefit the most from voice/data conver-
Introduction
The public telephone network and the equipment
that makes it possible are taken for granted in most
parts of the world. Availability of a telephone and
access to a low-cost, high-quality worldwide network is
considered to be essential in modern society
(telephones are even expected to work when the power
is off). Anything that would jeopardize this is usually
treated with suspicion. There is, however, a paradigm
shift beginning to occur since more and more commu-
nications is in digital form and transported via packet
networks such as IP, ATM cells, and Frame Relay
frames. Since data traffic is growing much faster than
telephone traffic, there has been considerable interest
in transporting voice over data networks (as opposed to
the more traditional data over voice networks).
Support for voice communications using the
Internet Protocol (IP), which is usually just called “Voice
over IP” or VoIP, has become especially attractive given
the low-cost, flat-rate pricing of the public Internet. In
fact, toll quality telephony over IP has now become one
of the key steps leading to the convergence of the voice,
video, and data communications industries. The feasi-
bility of carrying voice and call signaling messages over
the Internet has already been demonstrated but deliv-
ering high-quality commercial products, establishing
public services, and convincing users to buy into the
vision are just beginning.
VoIP can be defined as the ability to make
telephone calls (i.e., to do everything we can do today
with the PSTN) and to send facsimiles over IP-based
data networks with a suitable quality of service (QoS)
and a much superior cost/benefit. Equipment
producers see VoIP as a new opportunity to innovate
and compete. The challenge for them is turning this
vision into reality by quickly developing new VoIP-
enabled equipment. For Internet service providers, the
Technology Guide •
3
possibility of introducing usage-based pricing and
increasing their traffic volumes is very attractive. Users
are seeking new types of integrated voice/data applica-
the very least, will stimulate improvements in cost and
function throughout the industry.
Figure 1 illustrates one scenario for how telephony
and facsimile can be implemented using an IP
network. This design would also apply if other types of
packet networks (such as frame relay) were being used.
Successfully delivering voice over packet networks
presents a tremendous opportunity; however, imple-
menting the products is not as straightforward a task as
it may first appear. This Technology Guide examines
the technologies, infrastructures, software, and systems
that will be necessary to realize VoIP on a large scale.
Product development challenges such as ensuring inter-
operability, scalability, and cost/effectiveness will be
discussed. The types of applications that will both
drive the market and benefit the most from the conver-
gence of voice and data networks will be identified.
PC with
Fax Software
PC with
Voice Software
Fa
x
Intranet
Fa
x
Internet
Voice
Switch
Voice
Switch
Private Voice
Network
Phone
Phone
PSTN
Applications and Benefits
Fax
Phone
Voice communications will certainly remain a
basic form of interaction for all of us. The PSTN
simply cannot be replaced, or even dramatically
changed, in the short term (this may not apply to
private voice networks, however). The immediate goal
for VoIP service providers is to reproduce existing tele-
phone capabilities at a significantly lower “total cost of
operation” and to offer a technically competitive alter-
native to the PSTN. It is the combination of VoIP with
point-of-service applications that shows great promise
Figure 1: VoIP Infrastructure
VoIP could be applied to almost any voice
communications requirement, ranging from a simple
inter-office intercom to complex multi-point teleconfer-
encing/shared screen environments. The quality of
voice reproduction to be provided could also be
tailored according to the application. Customer calls
may need to be of higher quality than internal corpo-
rate calls, for example. Hence, VoIP equipment must
have the flexibility to cater to a wide range of configu-
rations and environments and the ability to blend
traditional telephony with VoIP.
The first measure of success for VoIP will be cost
savings for long distance calls as long as there are no
additional constraints imposed on the end user. For
example, callers should not be required to use a micro-
phone on a PC. VoIP provides a competitive threat to
the providers of traditional telephone services that, at
Technology Guide •
5
Some examples of VoIP applications that are likely
f) Internet call center access:
Access to call
center facilities via the Internet is emerging as a
valuable adjunct to electronic commerce applica-
tions. Internet call center access would enable a
customer who has questions about a product being
offered over the Internet to access customer service
agents online. Another VoIP application for call
centers is the interconnection of multiple call
centers.
a) PSTN gateways:
Interconnection of the Internet
to the PSTN can be accomplished using a gateway,
either integrated into a PBX (the iPBX) or
provided as a separate device. A PC-based
telephone, for example, would have access to the
public network by calling a gateway at a point
close to the destination (thereby minimizing long
b) Internet-aware telephones:
Ordinary
telephones (wired or wireless) can be enhanced to
serve as an Internet access device as well as
providing normal telephony. Directory services, for
example, could be accessed over the Internet by
submitting a name and receiving a voice (or text)
One of the immediate applications for IP
telephony is real-time facsimile transmission. Facsimile
services normally use dial-up PSTN connections, at
speeds up to 14.4 Kbps, between pairs of compatible
fax machines. Transmission quality is affected by
network delays, machine compatibility, and analog
signal quality. To operate over packet networks, a fax
interface unit must convert the data to packet form,
handle the conversion of signaling and control proto-
cols (the T.30 and T.4 standards), and ensure complete
delivery of the scan data in the correct order. For this
application, packet loss and end-to-end delay are more
critical than in voice applications.
Most VoIP applications that have been defined are
considered to be real-time activities. Store-and-forward
voice services will also be implemented using VoIP. For
example, voice messages could be prepared locally
using a telephone and delivered to an integrated
voice/data mailbox using Internet or intranet services.
Voice annotated documents, multimedia files, etc. will
also become standard within office suites in the near
future. The real-time and store-and-forward modes of
operation will need to be compatible and
interoperable.
Widespread deployment of a new technology
seldom occurs without a clear and sustainable justifica-
tion, and this is also the case with VoIP. Demonstrable
benefits to end users are also needed if VoIP products
c) Inter-office trunking over the corporate
intranet:
Replacement of tie trunks between
company-owned PBXs using an Intranet link
would provide economies of scale and help to
d) Remote access from a branch (or home)
office:
A small office (or a home office) could gain
access to corporate voice, data, and facsimile
services using the company’s Intranet (emulating a
remote extension for a PBX, for example). This
may be useful for home-based agents working in a
e) Voice calls from a mobile PC via the
Internet:
Calls to the office can be achieved using
a multimedia PC that is connected via the
Internet. One example would be using the
Internet to call from a hotel instead of using
expensive hotel telephones. This could be ideal for
submitting or retrieving voice messages.
Technology Guide •
7
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