Open Settlement Protocol

The OSP (Open System Protocol) is the European Telecom Standards Institute. Technical Specification 101 321 is used for Inter-Domain pricing, usage exchange and authorization.

It is the proven client/server protocol which is used by the ISPs (Internet Service Providers) to exchange authorization, accounting as well as using information with a view to provide support to the IP telephony. Moreover, the OSP protocol is also applied with PKI (Public Key Infrastructure) services to implement secure, multi-lateral VoIP on the un-secure networking environments like the Internet.
 
Firstly, the OSP is used as the short of a complete term i.e. Open Settlement Protocol.

Secondly, it is used as the short for term Online Service Provider.