The Open Settlement Protocol (OSP) is a client-server protocol (that consists of a set of protocols and associated profiles) defined by the ETSI TIPHON to establish authenticated connections between gateways/servers, and allows gateways and servers to transfer accounting and routing (optionally) information securely. OSP allows service providers to deliver multimedia services without establishing direct peering agreements with other service providers. It has XML based technical specifications and relies on HTTP and Transport Layered Security (TLS) for transport and is further independent of the call signaling protocols. With OSP a service provider is able to contact a clearinghouse, bandwidth brokers, and resource management servers and receive multiple routes that match the service provider’s criteria. The actual route costing and route selection is determined by a higher layer application. OSP is only used for transporting such information, not determining it. Billing or settlement information is sent in a UsageIndication message. This contains certain standard data elements, but also contains a sequence of UsageFields that can be extended as needed to carry additional data elements. There is a mechanism for a server to indicate specific UsageFields that it prefers or that it requires. UsageIndication can be sent multiple times during a call to send partial information or update previously sent data. Servers can specify call events
for which a client should send a UsageIndication. When calls are authorized, the server returns a token that proves this authorization. The token is carried in subsequent call signaling for that call and can be verified by the destination administrative domain. OSP is highly flexible in deployment: The different open settlement protocol features may be used independently of one another — for example, OSP could be used for call detail reporting, while call authorization is being done by a separate mechanism. The protocol provides access to the clearinghouse’s database of available service providers, but does not require any constraints on the policies implemented by the clearinghouse.
