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 or elsewhere."
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.
An interview with the authors: Speaking about VoIP
Chapter 7, Session Initiation Protocol and Related Protocols, is available free online
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