Open Settlement Protocol. The OSP Toolkit is a complete development kit for software developers who want to implement the client side of the European Telecommunication Standards Institute's (ETSI) OSP standard for secure VoIP peering. The OSP Toolkit includes source code written in ANSI C, test tools and extensive documentation on how to implement the OSP standard. A hosted OSP test server is freely available on the Internet for all developers to test their OSP implementation. External links European Telecommunications Standards Institute (ETSI) TIPHON project: Telecommunications and Internet Protocol Harmonization Over Networks TIPHON Release 4: ETSI Technical Specification 101 321 OSP Toolkit VoIP protocols Application layer protocols