online charging: considerations for accuracy, reliability ... · 2 online charging: considerations...

WHITEPAPER

Online Charging: Considerations for Accuracy, Reliability, and VisibilityAn Industry Whitepaper

Executive SummaryPerforming accurate, real-time usage metering is a requirement in most telecommunications markets.

The 3GPP standards specify that the measurement component—in practice the Policy and Charging Enforcement Function (PCEF) or Traffic Detection Function (TDF)—in the data path is a single logical entity that’s connected directly and in real-time to the online charging system (OCS) via Diameter Gy/Gyn; only in this architecture can a CSP avoid revenue leakage.

Many vendors claim that their solutions are 3GPP Gy/Gyn-compliant, even when they aren’t; typically, these non-compliant solutions include an intermediary node that breaks the direct, real-time connection and separates functions within the PCEF/TDF.

Non-compliance makes the charging deployment inaccurate and unreliable; furthermore, in such deployments, attempts to address one shortcoming (e.g., lack of accuracy) make the other one worse (e.g., lower reliability). The ultimate consequences for the CSP include increased cost and complexity, lower subscriber satisfaction, and—critically—revenue leakage.

Beyond architectural compliance, a second consideration for CSPs is the degree to which they have visibility into the charging system’s performance. Deep visibility into the right measurements and metrics satisfies a range of auditability, revenue assurance, and business intelligence use cases.

Understanding the issues at hand and the approaches used by vendors allows CSPs to make an informed decision and to invest in a solution that will actually work as needed.

ContentsExecutive Summary .............................................................. 1

Introduction to Online Charging ...................................... 2

Considerations for Online Charging ............................... 3

3GPP Standards Compliance .......................................... 3

Visibility into Charging Performance ............................ 8

Conclusion ................................................................................ 9

Online Charging Solution Requirements ..................10

Additional Resources .......................................................10

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Online Charging: Considerations for Accuracy, Reliability, and Visibility An Industry Whitepaper

Introduction to Online ChargingPerforming real-time metering of subscriber data consumption is a requirement in most telecommunications markets; this requirement is especially critical in prepaid markets where bite-sized Internet plans and time-based plans are effective revenue and differentiation strategies.

Accurate metering protects the revenue streams generated by these data services and prevents bill shock for subscribers due to under- or over-counting.

To standardize real-time metering solutions, the 3rd Generation Partnership Project (3GPP) defined a set of standards under the umbrella of the Policy and Charging Control (PCC) framework, as shown in Figure 1.

Figure 1: 3GPP PCC Architecture (adapted from 3GPP TS 23.203 Release 12)

Of particular relevance to real-time metering are the requirements that the measurement component—in practice, the Policy and Charging Enforcement Function (PCEF) or Traffic Detection Function (TDF)—in the data path is a single logical entity that’s connected directly and in real-time to the online charging system (OCS) via Diameter Gy/Gyn; only in this architecture can a communications service provider (CSP) avoid revenue leakage.

Beyond complying with the 3GPP standards from an architectural standpoint, a second consideration for CSPs is the degree to which they have visibility into the charging system’s performance. Deep visibility into the right measurements and metrics satisfies a range of auditability, revenue assurance, and business intelligence use cases.

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Considerations for Online Charging3GPP Standards ComplianceAccording to 3GPP TS 23.203, the PCEF/TDF is a single logical entity that performs service data flow detection, policy enforcement, and online and offline charging interactions. To ensure accuracy and timeliness, 3GPP standards describe online charging mechanisms as real-time processes requiring a direct, real-time interaction of the charging mechanism with data sessions and services via the Diameter Gy/Gyn interface. The charging mechanism encompasses both the OCS and the PCEF/TDF.

PCEFs and IntermediariesAdhering to the standards is vital to ensure accurate reporting and timeliness of the online charging mechanism. Many systems claim to be 3GPP Gy/Gyn-compliant but fail in real-world deployments: how can this apparent contradiction be reconciled?

There are two common ‘techniques’ by which a solution supplier attempts to justify a claim of 3GPP online charging compliance for a solution that actually fails to meet the standards:

1. Creative or partial interpretation and application of standards

2. Misrepresentation of components

The best way to understand these techniques is to critically examine them and to compare them to the actual meaning of the 3GPP standards for online charging. The figures below show three common online charging deployment scenarios, represented with a simplified view of the network.

Figure 2: 3GPP-compliant online charging deployment: direct, real-time connection

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Figure 3: This deployment is non-compliant: the charging connection is not direct and is not real-time

Figure 4: This deployment is non-compliant: the charging connection is still not direct and is still not real-time; in fact, this depiction highlights that the PCEF/TDF is not a single logical entity

Figure 2 is completely compliant with the 3GPP standard for an online charging deployment: the measurement component (i.e., PCEF/TDF) is a single logical entity and has a direct, real-time connection via Gy/Gyn to the online charging system

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In the deployment shown in Figure 3, the PCEF/TDF lacks Gy/Gyn. To obscure this shortcoming, the PCEF/TDF vendor has added Gy/Gyn to an intermediate node (e.g., a subscriber management component, or a mediation service), which now sits between the measurement function and the online charging system. In this scenario, the PCEF/TDF reports metering information to the intermediary, which subsequently processes the reports before passing usage to the OCS.

Critically, the “connection” between the PCEF/TDF and the OCS is now neither direct, nor real-time: this intermediate layer introduces significant delay (e.g., from a few minutes to as many as 30 minutes) and, when deployed at scale, guarantees billing problems of the kind discussed in the next section. In controlled laboratory settings and small scale deployments, this delay can be considerably reduced, but at production scale it re-appears and has significant consequences. It’s better to adhere to the standards and avoid the uncertainty, unpredictability, and risk that come with scaling a non-compliant architecture.

Figure 4 shows a deployment that’s functionally equivalent to Figure 3; the only difference is that the vendor misrepresents two completely separate components as being a single component. Without critically examining this claim, an evaluator might conclude that the “PCEF/TDF” actually is a single unit that really does have a direct, real-time connection to the OCS. However, strip away the superficial box drawn around the two components and their functional separation is clear. Once again, the “connection” between the actual PCEF/TDF piece and the OCS is nether direct, nor real-time.

If there was no difference in charging accuracy and reliability between these deployments, then non-compliance wouldn’t be of significant importance—but that’s not the case.

Implications for Charging AccuracyIn the indirect, interrupted connection depicted in Figure 3 and Figure 4, the timing between the PCEF/TDF and the intermediary node introduces significant challenges with charging accuracy, especially when deployed in high-speed networks (whether fixed access or mobile access).

In this architecture, the OCS grants limited user quota to the intermediary node. The intermediary node continuously monitors the service usage from the PCEF/TDF to ensure it does not exceed the granted amount. To meet the real-time accuracy requirements of 3GPP TS 32.251 and TS 32.299, the reporting frequency and thus the signaling load between the PCEF/TDF and the intermediary node are unrealistically high. In contrast, the directly integrated system shown in Figure 2 meets the 3GPP real-time requirements because metering and reporting are managed by a single platform with on-wire flow evaluation; hence, usage is reported immediately when the granted amount is reached.

Another serious issue with indirect integration is that accuracy errors grow quickly and proportionally with the number of subscriber services in place—severely hampering a CSP’s ability to launch a diverse set of revenue-generating subscriber services (e.g., with multiple tiers, special bolt-ons, zero-rated services, a range of purchase periods and volumes, etc.). Direct charging integration delivers superior predictability for the usage and revenue collection processes and, therefore, superior revenue assurance.

For more advanced deployments that leverage rating groups (i.e., multiple services are combined into a group) and service identifiers, indirect charging integration suffers even more. Whether or not the intermediate node is used to aggregate services into rating groups, the existence of an additional information transfer point amplifies error. For instance, if there are three services with 10% error, at the rating group level that error can sum to 30% inaccuracy. With direct integration there isn’t any error accumulation because usage from all services and rating groups is monitored using the same charging process; as a result, the likelihood of usage overshoot is reduced to the theoretic minimum.

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Furthermore, short-lived sessions pose unique challenges to the indirect integration model because the session might terminate before the intermediary node initiates the connection with the OCS1. In this scenario, the intermediary is unable to provide the right grant amount to the PCEF/TDF. The problem becomes much worse when PCRF signaling is needed in advance to approve a connection. As a result, with indirect and interrupted charging architectures, the CSP either suffers from significant revenue leakage or poor subscriber quality of experience (QoE) for services built around applications with short-lived sessions. And this is not an obscure corner case: short-lived sessions are extremely common today across a wide range of subscriber-centric and generalized network-wide use cases. In such cases, direct integration methods avoid revenue leakage or degraded QoE.

Finally, in deployments where data traffic flows on asymmetric routes2, the indirect architecture faces challenges in trying to ensure quota alignment between the PCEF/TDF and the intermediary node, resulting in even more revenue leakage. This deployment scenario is less of a challenge in systems that directly integrate with the OCS because quota alignment processing is minimal.

Implications for Charging ReliabilityIn addition to challenges with charging accuracy, systems that don’t integrate directly with the OCS suffer from significant challenges when it comes to reliability; these challenges are especially problematic when accuracy requirements are stringent because the signaling load between the PCEF/TDF and the intermediary node is high—more accuracy requires more signaling.

To ensure reliable transmission of charging reports between the PCEF/TDF and the intermediary node, deployment architects must consider trade-offs when choosing between using either a reliable (e.g., TCP) or unreliable (e.g., UDP) packet transport protocol: with a reliable transport protocol, packet retransmissions can result in network delays that increase the likelihood of revenue leakage resulting from overshoot; with an unreliable transport protocol, delay is minimized but packet (i.e., reporting) losses result in revenue leakage due to the loss of charging information for a measurement period.

In short, when using an indirect online charging architecture there is no guaranteed way to eliminate revenue leakage when it comes to transporting charging information between the PCEF/TDF and the intermediary node, which is why the 3GPP standard is strict about maintaining a direct, real-time connection between the PCEF/TDF and the OCS. The higher the accuracy requirements, the higher the signaling load, and hence the higher the likelihood of either retransmissions or packet losses resulting in even higher revenue leakage. These issues are insignificant within systems that directly integrate with the OCS.

An additional downside of the indirect architecture is increased overhead when connecting to a Network Management System (NMS), introducing higher cost and more complexity due to having more nodes.

1Examples range from instant messaging and weather applications to machine-to-machine (M2M) devices (e.g., smart meters and sensors that exchange small data bursts, parking meters that initiate and execute credit card transactions, etc.)—short sessions are prevalent, and they’re here to stay

2In such a deployment, an individual PCEF/TDF may only see (i.e., count) part of the data associated with a subscriber or device; in this scenario, information from multiple PCEF/TDF devices must be brought together. You can learn more about routing asymmetry in general, and its implications for network policy control, in Applying Network Policy Control to Asymmetric Traffic: Considerations and Solutions

https://www.sandvine.com/downloads/general/whitepapers/applying-network-policy-control-to-asymmetric-traffic.pdf

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Support for Popular Use CasesWith increasing frequency, CSPs are introducing subscriber services that rely on accurate, reliable online charging solutions. Table 1 examines some of these popular use cases and compares the potential for revenue leakage using the two billing architectures examined in this paper.

Table 1: The impact of online charging architecture on revenue leakage for popular use cases

Use Case

Potential for Revenue Leakage

Additional NotesPCEF/TDFgOCS:

• Direct• Real-Time

PCEF/TDFgOCS:• Not Direct• Not Real-Time

Basic Data Plans None or minimal Medium The revenue leakage in the indirect integration case increases as a function of the connection link speed.

Differentiated or Tiered Plans None or minimal Medium to High Such data plans often seek differentiation with time-based

billing, which brings problems to light very quickly.

Roaming None or minimal High Subscribers’ usage is not accounted for and operators still need to pay data transit costs to their transit partners.

Tethering None or minimal Medium to HighMore PDP contexts are created in this case and hence more accuracy and reliability issues between the PCEF and the intermediary node.

Smartphone Plans None or minimal Medium to HighMore PDP contexts are created in this case and hence more accuracy and reliability issues between the PCEF and the intermediary node.

Shared/Family Plans None or minimal Very High

Inaccuracies are proportional to the average number of devices per user, number of PDP contexts per device, and number of services and rating groups that need to be tracked; if subscribers are roaming, then revenue leakage is much worse.

Enterprise (high value subscribers) group accounts

None or minimal Very High

Indirect integration architecture performs poorly when it comes to supporting modern enterprise packages (e.g., enforcing usage caps or speed limiting for small businesses, enforcing usage caps on a per department basis, sending timely notifications to business users during roaming about their roaming charges).

Machine-to-Machine and the Internet of Things

None or minimal Very HighShort sessions are a big challenge to indirect architectures and hence suffer from significant challenges in M2M deployments.

Prepaid Plans None or minimal High Revenue leakage can be a significant percentage in cases of small quota with prepaid packages.

Zero-Rating None or minimal Medium to High Under-counting zero-rated bytes over-charges subscribers; over-counting zero-rated usage causes revenue leakage.

Time-of-Day Bundles None or minimal Medium

Time-of-day bundles are sensitive to the accuracy of usage charging before and after the time when the charging rate changes. It is important to ensure a clean and accurate split between charging periods (much easier with direct OCS integration due to the timeliness); with indirect architectures, delays and time synchronization between the PCEF and the intermediary node can result in revenue leakage in such cases.

Public Promotions and Loyalty Campaigns

None or minimal Low

Depending on the number of users enrolled in a promotion, usage can be inaccurately attributed to base plans rather than to the promotional bundles, resulting in a confusing experience.

Sponsored Connectivity None or minimal Medium

Due to delays applying zero-rating on sponsored content, the subscriber might be penalized for promotional content or the operator might lose revenue when sponsored connectivity is no longer valid, resulting is zero-rating billable usage.

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Visibility into Charging PerformanceDeep measurements and metrics allow a CSP to analyze the functionality and performance of the online charging deployment. Table 2 explains how particular measurements and metrics address a number of example scenarios.

Table 2: Example scenarios addressed by deep charging measurements and metrics

Since the metrics and measurements available vary enormously by solution vendor, it is vital that a CSP ask detailed questions and clearly understand how particular scenarios are addressed.

Scenario/Situation Measurements and Metrics Description/Explanation

OCS is Unreachable, or Back-Up Recovery Scenario

Maintain measurement of subscriber usage when there is no active Gy/Gyn connection to the OCS

Measuring usage while the OCS is unreachable helps to ensure that most revenue is recovered during an outage; however, some leakage remains due to users going out-of-balance while the OCS is unavailable.

Out of Credit AuditingInspect whether a Final Unit Indication (FUI) was signaled by the OCS

By inspecting the Final Unit Indications and the Out of Credit result codes, CSPs gain visibility into how many subscribers and sessions are out of credit, and are subsequently able to determine the appropriate action.

Armed with this information, a CSP can correlate these results with subscriber characteristics like APN, demographic, plan size, location, etc.

OCS Health Check-Up

Monitor the performance of Gy/Gyn signaling with the OCS, including:

• Functionality of a rating group and service identifier

• Reporting reasons per service

• Assigned quota holding times and volume/time quota thresholds

With these measurements, CSPs are able to monitor the health of the charging operation, and thus the rating and revenue collection by the OCS.

This insight allows a CSP to focus on areas of concern, for instance:

• The OCS (e.g., delays due to connecting to a separate balance management server covering certain rating groups, etc.)

• The network connectivity to the OCS (e.g., Diameter signaling retransmissions, long delays/jitter to some OCS servers, etc.)

• Comparing operational metrics for multiple OCS vendors in mixed deployments (e.g., OCS vendor #1 serving prepaid use cases and OCS vendor #2 serving postpaid use cases)

Diameter Performance Monitoring

Track the number of sessions, response latency, and Diameter retransmissions

These measurements provide visibility into the efficiency of the charging network.

Customer-Driven Reports or On-Demand Customer Auditing

Log all flows, all HTTP URLs, and offline usage for a specific user (or for all users)

If a subscriber is suspected of having billing issues (e.g., a subscriber makes frequent dispute calls), then customer support can enable detailed reporting for the specific user. These audit reports show the rules and rating groups applied to each subscriber flow, and provide the CSP with detailed information for dispute resolution.

Alternatively, CSPs may choose to enable detailed reporting for all subscribers, as a matter of course.

Zero-Rated Data Reports

Measure all bytes sent and received for a user and compare to a standard profile

By examining traffic, CSPs are able to identify abnormal zero-rating behavior that is a potential indicator of fraud.

Usage Auditability ReportsReconcile and compare data usage between the PCEF/TDF and the OCS

This reconciliation and comparison alerts CSPs of any discrepancies with usage reporting across systems and creates confidence in the charging capabilities, as well as providing back-up measurements in case of a failure scenario.

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ConclusionTo provide a standard model for deploying real-time metering solutions, the 3GPP defined a set of standards. Of particular relevance to real-time metering is the requirement that the PCEF/TDF is a single logical entity that’s connected directly and in real-time to the OCS via Diameter Gy/Gyn.

Many systems claim to be 3GPP Gy/Gyn-compliant but fail in real-world deployments because the claims are false. Figure 5 shows three diagrams that represent two charging architectures:

• The left-most architecture is compliant with 3GPP online charging standards: the PCEF/TDF is a single logical entity and the connection between the PCEF/TDF and the OCS is both direct and real-time

• The middle figure is not compliant: the introduction of an intermediate processing node breaks the direct connection and breaks the real-time nature of the usage reports

• The right-most figure has an identical architecture to the middle figure, but the diagram has a superficial box misrepresenting two separate components as one: this box does not rectify the indirect, non real-time nature of the architecture

Figure 5: Three diagrams representing two charging architectures: only the left-most diagram is compliant with 3GPP standards for online charging

From the CSP’s perspective, failure to adhere to the strict 3GPP standards for online charging results in revenue leakage and unreliable billing for all online charging use cases. The degree of revenue leakage varies by use case based upon a handful of factors, so each must be considered separately.

The only way for a CSP to achieve minimum revenue leakage and maximum reliability is by adhering to the 3GPP requirements.

Beyond architectural compliance, a second consideration for CSPs is the degree to which they have visibility into the charging system’s performance. Deep visibility into the right measurements and metrics satisfies a range of auditability, revenue assurance, and business intelligence use cases.

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Online Charging Solution RequirementsThe requirements for an accurate, reliable, 3GPP-compliant online charging solution are quite straightforward:

Additional ResourcesThank you for taking the time to read this whitepaper. We hope that you found it useful, and that it contributed to a greater understanding of online charging deployment architectures and considerations.

In addition to the 3GPP resources cited in this document, please consider reading the Sandvine technology showcase: Standards-Compliant Online Charging, available on www.sandvine.com.

If you have any feedback at all, then please get in touch with us at [email protected].

Consideration Requirement Explanation

Usage Measurement

The measurement component (i.e., PCEF/TDF) must measure data usage in real-time

To decrement from prepaid quota in real-time, the data usage must be measured in real-time (as opposed to later via a records system).

Gy/Gyn Connection between Measurement Component and Online Charging System

Gy/Gyn connection between the measurement component and the online charging system must be direct (i.e., no intermediate processing node)

This architecture is the only way to ensure accuracy and reliability in real-world networks.

Gy/Gyn connection between the measurement component and the online charging system must be real-time (i.e., no interruption, aggregation, etc.)

This architecture is the only way to ensure accuracy and reliability in real-world networks.

Visibility into charging deployment measurements and metrics

Deep reporting key performance indicators, in general, with specific requirements determined by use case

These measurements and metrics provide CSPs with audit data, business intelligence insight, redundant records, etc.

https://www.sandvine.com/downloads/general/sandvine-technology-showcases/standards-compliant-online-charging.pdf

https://www.sandvine.com/

mailto:[email protected]

This whitepaper is published by Sandvine Incorporated ULC©. All rights reserved. No part of this publication may be reproduced, copied or transmitted in any form or by any means, or stored in a retrieval system of any nature, without the prior permission of Sandvine Incorporated ULC. Although the greatest care has been taken in the preparation and compilation of this whitepaper, no liability or responsibility of any kind, including responsibility for negligence is accepted by Sandvine Incorporated ULC.

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online charging: considerations for accuracy, reliability ... · 2 online charging: considerations...

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