Towards 5G Network - Basics of Telecom Offline Charging

Basics of Telecom Offline Charging

This is the second article in the series Telecom Charging: Journey towards 5G Network and shares the basics of Offline Charging in a Telecom Network.

(Click to enlarge) Role of Mediation in Telecom Offline Charging

Please refer Towards 5G Network - Basics of Telecom Online Charging to read the first article of this series which talks about the basics of Online Charging.

Offline Charging allows Subscribers to consume the service without an upfront balance check or balance reservation. Post Service consumption, Service usage records are processed in the form of files & batches for charging the Customers. These service usage files are also known as Charging Data Records (CDRs) or Event Data Records (EDRs).

As it's not practical to send this large no. of files (which can be of different formats) through different Network nodes directly to the billing system, they are first mediated via a system known as Mediation. It sits between the Network layer and the BSS layer.

Mediation system performs operations like:-

• Raw CDR collections via PUSH or PULL method. CDR file formats can be ASCII, CSV, Binary, TAP, XML, etc.
• Validating, Filtering & Parsing the CDRs.
• 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.

Let's see how the Offline Charging mechanism works for a Service usage:-

• The customer initiates service usage.
• Raw CDRs are generated for 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 the 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 to the Bill.
• Bill gets generated for initiating Customer payments.

(Click to enlarge) Offline Charging, Mediation, Rating, and Billing in a nutshell

Offline Charging supports Session-based (like Voice calls or YouTube browsing) as well as Event-based (like SMS and file transfer over Instant Messaging) services. Operators use the Credit limit of the Customers for the service allowance. Revenue leakage will be minimal when the CDRs are rated as soon as they are generated during service usage.

Let's understand the Offline Charging mechanism as per the 3GPP standard:-

(Click to enlarge) Offline Charging Architecture as per 3GPP

The above figure explains the Offline Charging architecture as per the 3GPP standard.

CTF (Charging Trigger Function): This is the network node that generates charging triggers whenever a Customer uses services. Examples are GGSN, PGW, SMSC, etc. It sends Diameter Accounting-Request (ACR) messages to CDF for the generation of Raw CDRs.

CDF (Charging Data Function): This network node generates Raw CDRs by processing ACR/ACA messages based on service consumption. On receiving ACRs, CDF processes the offline charging info and generates the CDRs.

Using Accounting Answer (ACAs) messages, it notifies the CTFs that the Charging record has been generated.

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

Billing System: Usage records received from CGF (or Mediation) are rated by the Rating Engine. Rated Event data gets generated and stored. Billing process consumes the rated events stored in the database and adds up the Usage charges against the Customer's bill. During Bill Run, charges like monthly recurring charges, one-time charges, cancellation charges, etc. are also processed along with usage charges. Other activities like billing time discounts, adjustments, settlements, taxes, etc. are also considered during the Bill Run. Once the Bill is finalized, it becomes ready to accept the Payments against the Invoice.

In the upcoming articles on this series, details about 5G Network Converged Charging will be covered. 

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Glossary: AAA (Authentication, Authorization & Accounting Server), 3GPP (3rd Generation Partnership Project), BSS (Business Support System), OSS (Operations Support System), RA (Revenue Assurance system), FMS (Fraud Management system), TAP (Transferred Account Procedure files), GGSN (Gateway GPRS Support Node), PGW (PDN Gateway), SMSC (Short Message Service Center)

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