August 14, 2002
Build Your Own VoIP System with O'Reilly's Latest Release, "Practical VoIP Using VOCAL"
Sebastopol, CA--VoIP, or Voice over Internet Protocol, is the
technology that allows people to make telephone calls over the
Internet, limiting long-distance charges to the nominal cost of email.
The software for making these "free" long-distance calls has been
available for years. Although early versions suffered from poor
quality, users were willing to endure packet loss, jitter, and latency
in return for bypassing normal long-distance toll charges. Today,
improvements in VoIP software and better bandwidth and processing speed
have made conversation through VoIP devices practical and increasingly
cost-effective. For those who are interested in building their own VoIP
system, O'Reilly's just-released, Practical VoIP Using VOCAL by Luan
Dang, Cullen Jennings, and David Kelly (US $44.95), describes how such
a phone system is actually built, and how you too can acquire the
source code, install it onto a system, connect phones, and make calls.
"VoIP is a set of rules, also known as protocols, and devices that
enable users to make phone calls over the Internet," explains coauthor
Dang, who is also cofounder of Vovida Networks. "VoIP systems transmit
signals to set up and tear down calls and media to make it possible for
users to hear each other talk. These signals and media are sent over
networks as packets just like other forms of data. Another term for
VoIP is 'packet telephony.'
"More and more organizations are installing VoIP systems to make better
user of their networks," Dang adds. "If you are already using a large
network for sharing text and images, it is not a large technical leap
to deploy a VoIP system on the same network. Open source systems, such
as VOCAL, help make setting up VoIP networks cost effective."
VOCAL (the Vovida Open Communication Library) is an open source
software project that provides call control, routing, media, policy,
billing information, and provisioning on a system that can scale from a
single box in a lab with a few test phones to a large, multihost
carrier grade network supporting hundreds of thousands of users. VOCAL
is freely available from the Cisco systems-sponsored Vovida.org
community web site. Because VOCAL is open source, users can look "under
the hood" down to the base code and protocol stack levels and discover
not only how the system works, but also how common problems are being
worked out in the development environment.
"VOCAL empowers the end user with control over feature development and
customized integration with legacy systems," says coauthor Jennings.
"Along with all other VoIP applications, VOCAL is actively inverting
the way that telephony is deployed by allowing an Internet-style
anarchy that was never possible in the traditional PSTN (Public
Switched Telephone Network). It has been a fun area to work in."
"Practical VoIP Using VOCAL" shows system administrators and
programmers how to implement, program, and administer VoIP systems
using open source tools. It is a practical, hands-on guide that
provides background and real-world examples for provisioning and
administering VoIP systems. Readers will learn how to install and
configure VOCAL 1.4.0 onto a single host and onto a multihost network
with phone and gateways. The book also covers:
- C++, C, and Java architecture found within VOCAL
- Provisioning a VoIP system
- SIP (Session Initiation Protocol), SDP (Session Description Protocol),
and RTP (Real-time Transport Protocol) for call control and media
- TRIP (Telephony Routing over IP), DNS SRV, and ENUM for routing
- MGCP (Media Gateway Control Protocol) and H.323 for call control and
translation into SIP
- COPS (Common Open Policy Service), OSP (Open Settlement Protocol), and
RSVP (Reservation Protocol) for policy and Quality of Service
- RADIUS (Remote Authentication Dial In User Service) for interfacing
with billing servers
- SNMP (Simple Network Management Protocol)
"For many readers, especially those who have no prior knowledge of
VOCAL or Vovida.org, 'Practical VoIP Using VOCAL' will provide them
with their first opportunity to download, test, and analyze the
software" says coauthor Kelly. For those who have already worked with
VOCAL, this book provides much greater detail about the data structures
found within the code than any other material available on the web site
If you are interested in VoIP, "Practical VoIP Using VOCAL" is the only
book available that focuses on the real issues facing programmers and
administrators who need to work with these technologies.
Practical VoIP Using VOCAL
By Luan Dang, Cullen Jennings, and David Kelly
ISBN 0-596-00078-2, 502 pages, $44.95 (US), $69.95 (CAN)
O'Reilly Media spreads the knowledge of innovators through its books, online services, magazines, and conferences. Since 1978, O'Reilly Media has been a chronicler and catalyst of cutting-edge development, homing in on the technology trends that really matter and spurring their adoption by amplifying "faint signals" from the alpha geeks who are creating the future. An active participant in the technology community, the company has a long history of advocacy, meme-making, and evangelism.
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