Practical VoIP Using VOCAL

OSP

OSP is a proposed European Telecommunications Standards Institute (ETSI) specification for providing interdomain authentication, authorization, pricing information, and accounting standards for IP telephony. We obtained an OSP stack from TransNexus, Inc. (http://www.transnexus.com) and wrote C++ wrappers to enable their stack, which was written in C, to work with our Policy server.

While we provide the client side of OSP, on http://Vovida.org, there is an application called OpenOSP that provides the server side of an OSP solution. The server side is geared toward the role that a third party would fill as a trusted broker.

One of the components of the OSP and Policy server architecture is the Secure Socket Layer (SSL) transport layer security toolkit. We downloaded our toolkit from the OpenSSL site (http://www.openssl.org).

Making Internetwork Calls

Figure 18-4 shows User Agent (UA) A initiating a call to User Agent B. In this scenario, the UAs are used together with basic analog phone sets and are attached to different VOCAL systems, and each VOCAL system is known to the others. The call signal routing is carried over the Internet.

The call may be routed through one or more Feature servers before it reaches the Internetwork Marshal (INMS). For the sake of clarity, the Feature servers have been omitted from this scenario.

VOCAL supports multiple Internetwork Marshal servers (INMSs). Each of these servers will accept off-network INVITE messages from one other known SIP-based ...