OSP is VoIP peering protocol and is the international standard for Inter-Domain pricing, authorization and usage exchange of IP communications. The OSP standard is defined by TISPAN of the European Telecommunications Standards Institute (ETSI) www.etsi.org. The OSP standard is officially known as ETSI Technical Specification 101 321. Version 1.4.2 of this standard was ratified in December 1998. Version 4.1.1 of the OSP standard was ratified in November 2003 and may be downloaded here, ETSI TS 101 321 V4.1.1 (2000-11).
Benefits
The major benefit of OSP for VoIP carriers is it provides a single, highly secure mechanism for managing diverse VoIP networks. OSP provides a common interface between VoIP networks and the operations and billing support systems (OSS/BSS) used to manage VoIP networks. By using a global VoIP to OSS/BSS interface, carriers are now enabled to build and manage multi-vendor, multi-protocol networks without impacting their central routing and billing operations. The benefits are greater flexibility, vendor independence and lower operating costs.
Features
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Common peering mechanism for diverse VoIP networks.
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Digitally signed peering tokens enable secure, ubiquitous peer to peer communications
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Interdomain access control much more secure and scalable than IP access lists.
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Common, standard Call Detail Record (CDR) for diverse VoIP networks.
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Real time collection of CDRs from both source and destination networks.
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CDR collection can be encrypted using SSL ensuring secure data collection.
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High CDR integrity minimizes settlement disputes.
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OSP messages are XML based which are easy to read, manipulate and extend.
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Supports both H.323 networks, SIP networks and can support other IP transaction models.
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Broad vendor support.
Overview of OSP
The OSP standard defines fourteen messages which can be used to convey peering authorization and capabilities. This document focuses on the six messages most commonly used to manage VoIP peering. These six messages typically occur between an OSP client such as a VoIP gateway, SIP Proxy or softswitch and an OSP Server. These messages, written in italics, are:
1. AuthorizationRequestThe message sent from an OSP client (i.e. source gateway) to the OSP Server requesting one or more routes and authorization to a destination gateway that can complete the call to the dialed number.
2. AuthorizationResponse:The response from the OSP Server to the AuthorizationRequest from a source gateway. This message includes one or more IP addresses of destination devices that can complete the VoIP call to the dialed number. Each destination IP address is accompanied with an authorization token digitally signed by the OSP Server. The authorization token is included in the call set-up request from the source device to the destination device. The destination device validates the token before accepting the call set-up request from the source device.
3. UsageIndication: This message is the OSP defined message for reporting usage. The source and destination devices automatically send a UsageIndication message to the OSP Server when the call is completed.
4. UsageConfirmation: The OSP Server responds to each UsageIndication message with a UsageConfirmation message. A source or destination device will continue to send a UsageIndication message for a call until it receives a UsageConfirmation from the OSP Server.
5. CapabilitiesIndication: This versatile message is sent from an OSP client to an OSP Server. The OSP client may use the capabilities exchange message to transmit the following information to an OSP Server:
a. Serial number and customerID (can be used for self provisioning)
b. Services requested from the OSP Server (i.e. routing, accounting or both)
c. OSP version supported
d. Available bandwidth and channel resources (a client can indicate to an OSP Server that it should be added or removed from routing based on its available resources.)
6. CapabilitiesConfirmation: The OSP Server responds to each CapabilitiesIndication message with a CapabilitiesConfirmation message.
Simple OSP Call Scenario
A single OSP Server authorizes a peer to peer call between two voice over IP gateways. The originating (source) peer makes an OSP AuthorizationRequest to the OSP Server for the IP address of a terminating (destination) peer that can complete the call to the dialed number. The OSP AuthorizationResponse includes the IP address of the terminating (destination) peer and a peering authorization token digitally signed by the OSP Server.
The originating (source) peer includes the peering authorization token in the call set-up to the terminating (destination) peer. An peering authorization token can be included in a Q.931 call set-up message or in a SIP INVITE message. The terminating gateway recognizes the authorization token in the call set-up, validates that the authorization token was digitally signed by a trusted peering authority.
As shown in the illustration below, when the call ends, the originating and terminating gateways send their UsageIndication messages to the OSP Server. The OSP Server responds by sending a UsageConfirmation message (not shown) to the originating and terminating gateways.
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