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Online Charging System

OCS is a specialized transmission function that permits an assistance provider to charge a user for services in real-time. The OCS handles the subscriber’s account balance, assigning transaction control, correlation, and rating. In addition, OCS assists a telecom operator in ensuring that credit limits are enforced and resources are authorized based on transactions.

Traditional online charging systems charge the Customer after a service is generated, whereas the OCS charges as services are developed. Therefore, OCS is more flexible than Intelligent Network (IN) prepaid solutions.

 1. Architecture

   1.1 Event-Based Charging

  1.2 Session-Based Charging

    1.2.1 Account and Balance Management

Online charging system overview (Source- researchgate.net)

Event Based Charging

An Event-Based Charging Function (EBCF) is employed to seize events based on their happening, preferably than their course or volume used in the event. Typical events include SMS, MMS, and content purchase (application, game, music, on-demand video, etc.).

The event-based charging operation is employed when the CC-Request-Type AVP = 4, i.e., for event proposal ex: diameter-SMS or diameter.

Let us assume a sample of Event-based Charging. 

  1. Cost of one apple is Rupees 25/- You pay the amount, take the apple and go. Likewise, sending a text message may cost you Rupee 1/- and that’s it. But, on the other hand, you subscribe to Caller Ring Back Tone (CRBT), which costs you Rs.30/- a month, irrespective of the number of calls you receive in a month. Therefore, we can term event-based Charging as a one-time or one-time occurrence cost.


Session Based Charging

The session-based charging function (SBCF) is responsible for the online Charging of network/user sessions, e.g., voice calls, IP CAN bearers, IP CAN offer sessions or IMS sessions.

Let us consider an example of session-based Charging. Utility services like electricity or water are charged based on overall usage for a specific time duration. For instance, you consume ‘x’ power units in a month and pay for units engulfed in that month. However, the use may vary monthly and hence the charges, similarly for drinking water, etc. Therefore, charging based on how much one consumes is metered or session-based.


Account and Balance Management

The account balance management function (ABMF) is the subscriber’s account balance location within the OCS.

LTE OCS-Online Charging System | OCF-Online Charging Function

Online charging architecture (source- rfwireless-world)

In OCS, charging events are received by the “Online Charging Function (OCF). ”
The OCF decides about the usage of resources based on the Rating Function (RF) and Account Balance Management Function (ABMF).
CTF stands for Charging Trigger Function.

Offline Charging System

Offline Charging authorizes Subscribers to consume the benefit without an upfront balance check or reservation. Post Service consumption and usage logs in the state of files & batches are processed for charging the Customers. These service usage files are called Charging Data Records (CDRs) or Event Data Records (EDRs).

As it’s not practical to send this large no. of files (different formats) through other Network nodes directly to the billing system, they are first adjudicated through a technique known as Mediation. It models between the Network layer and the BSS layer.

Mediation in offline charging (Source- RajarshiPathak)

Mediation system performs operations like: –

  • Raw CDRs Collections via PUSH or PULL method. CDRs file format can be ASCII, CSV, Binary, TAP, XML, etc.
  • Validating, Filtering & Parsing the CDR’s.
  • Processing/Enriching the records as per the Northbound systems (like Rating Engine, Interconnect System, Roaming Clearinghouse, RA, FMS, Reporting, etc.) requirements.
  • Distributing the processed CDRs to Northbound systems.

Offline Charging mechanism works for Service usage: –

  • Customer initiates service usage.
  • Raw CDRs get generated about this usage. Usage can be Session-based (e.g. Video call) or Event-based (e.g. File transfer/SMS).
  • Accounting-Request (ACR) and Accounting Answer (ACA) Diameter Messages are used to construct CDRs for service usage.
  • Raw CDRs are collected and processed by the Mediation system.
  • Processed CDRs from Mediation are guided to the Rating Engine.
  • CDRs are rated by Rating Engine as per the rate plans by measuring the events.
  • Rated Event data gets generated and stored in the Billing system.
  • Billing process picks up these rated events during the bill run for calculating the Usage charges to be applied on the Bill.
  • Bill gets generated for initiating Customer payments.

Source- netmanias.com

Offline Charging supports Session-based (like Voice calls or YouTube browsing) and Event-based (like SMS, File transfer over Instant Messaging) services. In addition, operators use the Customers’ credit limit for the service allowance. Therefore, revenue leakage will be minimal when the CDRs are rated as soon as they are generated during service usage.

Offline Charging mechanism as per 3GPP standard: –

Source- netmanias.com

CTF (Charging Trigger Function): The network node generates charging triggers whenever a customer uses services. Examples are GGSN, PGW, SMSC, etc. In addition, it sends Diameter Accounting-Request (ACR) messages to CDF to generate Raw CDRs.

CDF (Charging Data Function): This network node renders Raw CDRs by processing ACR/ACA messages established on service consumption. On obtaining ACRs, CDF processes the offline charging information and induces the CDRs. Using Accounting Answer (ACAs) messages, inform the CTFs that the Charging record has been developed.

CGF (Charging Gateway Function): The Mediation system processes the Raw CDRs and transmits the processed CDRs to the BSS systems. More details of Mediation are mentioned above.

Billing System

Use documents obtained from CGF (or Mediation) are placed by the Rating Engine. Rated Event data gets generated and stored. The billing process consumes the rated events held in the database and counts the Usage charges against the Customer’s Bill. During Bill Run, expenses like monthly recurring, one-time, cancellation, etc., are also processed along with usage charges. In addition, actions like billing term deals, adjustments, compensations, taxes, etc., are also assessed during the Bill Run. Once the Bill is concluded, it accepts the Payments against the Invoice.

Related Tags: payment, online charging, offline charging, billing, security, taxes, charging data, charging gateway, data management.

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