While many books describe the theory behind Voice over IP, only Practical VoIP Using VOCAL describes how such a phone system was actually built, and how you too can acquire the source code, install it onto a system, connect phones, and make calls.
VOCAL (the Vovida Open Communication Application Library) is an open source software project that provides call control, routing, media, policy, billing information and provisioning on a system that can range from a single box in a lab with a few test phones to a large, multi-host carrier grade network supporting hundreds of thousands of users. VOCAL is freely available from the Cisco Systems-sponsored Vovida.org community web site (www.vovida.org).
A Silicon Valley start-up called Vovida Networks, Inc (think of VOice, VIdeo, DAta) created VOCAL and invested over one hundred man years into its development. Since Cisco acquired Vovida in 2000, individuals representing every significant telecom company and service provider in the world have downloaded the source code. Today, more and more people are successfully building VOCAL into professional solutions, while contributing fixes and new functionality back to Vovida.org.
Because VOCAL is open source, you can look "under the hood" 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. We're hoping that you will be inspired to take this system to another level by implementing a feature or functionality that no one has thought of before.
Written by a team from Vovida Networks, Practical VoIP Using VOCAL includes the following topics
Installing and configuring VOCAL 1.4.0 onto a single host and onto a multi-host network with phones and gateways
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)
If you're interested in VoIP, this is the only book available that focuses on the real issues facing programmers and administrators who need to work with these technologies.