The Sentinel framework, which Sentinel VoLTE is based on, uses the Diameter Ro interface to the OCS to enable online charging. The charging over Diameter Rf is done via Rf Control Resource Adaptor.

For more details on this please see the Sentinel product documentation and Rf Control Resource Adaptor Architecture.

Highlighted below are the key pieces of charging functionality:

Multiple OCS support

Support of multiple OCSs is a key requirement for the session control element, for several reasons:

  • During migration of an operator’s charging infrastructure, it is likely that more than one OCS will need to be supported.

  • The CSP may have different OCSs for prepaid and post-paid, and/or different OCSs for voice/SMS and data.

  • Multiple MVNOs may be hosted on an operator’s network, each with their own OCS.

scc services charging

Sentinel is designed to provide session control on behalf of multiple OCSs. Sentinel determines which OCS to send the charging messages to in real time at session initiation. Different schemes may be utilised to determine the correct OCS. For example, it might be done by subscriber location, or attached network, or a real-time lookup to an external real-time database, or based on the APN used by the subscriber.


In the middle of a SIP session, media streams may be added and removed, as well as having their codecs changed. When codecs change, Sentinel VoLTE consults its SDP codec configuration to determine if the change was a “meaningful” change from a charging perspective (for example, if an audio call was changed to an audio and video call).

If a change is deemed meaningful, Sentinel performs client-initiated re-authorization towards the Online Charging System. If a change is not meaningful, the current credit reservation remains valid. This is explained in more detail in the Charging support section.

CDR generation

Rhino Sentinel writes a CDR for all charging session attempts, whether the session was successfully completed or could not be completed due to some error.

CDRs generated by Sentinel may also be used for offline charging situations.

The CDRs are written to a file in a configurable location and contain all the parameters that are available to the Rhino Sentinel. More detail on Sentinel VoLTE CDRs can be found in the Charging Information section of the Sentinel VoLTE Administration Guide.

Offline charging via Diameter Rf

VoLTE sends charging information to a configured Charging Data Function via Diameter Rf interface.

The Rf Control Resource Adaptor receives request from VoLTE charging features and ensure the messages are persisted in the CDF or in a local disk buffer is case the CDF is not available. As soon as the CDF is available it will send the messages stored locally until the buffer is empty.

For more information see Rf Control Resource Adaptor Architecture.

Use of a Prepaid SCP via CAP

Sentinel VoLTE can be installed to use a Prepaid Service Control Point as the OCS, rather than communicating via Diameter Ro to the OCS. The use of Ro, CAP or neither for online charging is enabled through the Selection of charging mode. In all cases, Sentinel VoLTE will write a CDR for the session.

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