Overview

The SMF acts as a Charging Transfer Function (CTF). The CTF generates charging events toward the Charging Function (CHF), which is responsible for generating Charging Data Records (CDRs).

This SMF NF interacts with various interfaces such as N40, N4, N7, and N10, facilitating charging in entirety. Currently, the Cisco SMF uses the Nchf/N40 interface to generate charging events.

SMF as a Charging Transfer Function

The SMF Charging feature supports the following functionality:

  • Converged Online and Offline charging.

  • PDU session charging using the service-based interface.

  • Network slice instance charging.

  • Charging information collection per PDU session for UEs served under 3GPP access.

  • Each PDU session is assigned a unique identity number for billing purposes.

  • Data volumes on both the uplink and downlink directions are counted separately. The data volumes reflect the data as delivered to and forwarded from the user.

  • The charging mechanism provides the date and time information when the PDU session starts.

  • The SMF handles Charging Characteristics specific to a subscription or a subscribed DNN.

  • The SMF identifies data volumes, elapsed time, or events for individual service data flows (flow-based charging). One PCC rule identifies one service data flow.

  • SMF allows usage reporting of a service or a detected application per rating group or per combination of the rating group and service ID. This reporting level can be activated per PCC rule.

  • Quota management is done per Rating Group (RG) per PDU session.

  • SMF supports charging for IP-based PDU session types.