PROCEDIMIENTOS DE AUDITORIA

mes-sage. Note that the CCR message indicates that the Rating-Group is “Group B’’ listed in Table 9.7. The Service-Identifiers are “IMS Video’’ and “IMS Audio’’. The OCS calculates the reserved credit for the IMS audio and video service flows according to the tariff plan of Group B. In this example, both the IMS audio and video service flows are charged by time duration. The tariff rates for these service flows are $1 and $0.50 per minute, respectively.

Step 15. When the reservation is finished, the OCS replies to the TPF with the CCA message to indicate the amount of granted credit. At this point, the IMS call (including the audio and the video streams) can be delivered to the UE.

The TPF allows the IMS media packets to pass through the GGSN. It also calculates the time period for these service flows.

When the IMS call is finished, the TPF sends the charging information to the OCS.

The OCS deducts the consumed credit units from the subscriber’s account based on the tariff of different service flows. In the above example, we assume that the IMS signaling and the IMS media packets are transferred within the same PDP context and QoS pro-file. The reader is encouraged to redraw the message flow such that the IMS signaling and the IMS media are transferred through two individual PDP contexts (i.e., with dif-ferent QoS profiles). In this case, the UE needs to activate the secondary PDP context.

9.4 Policy and Charging Control Integration

Today, the network resources consumption varies considerably among subscribers generally charged the same flat rate for Internet access, where telecom operators are

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not able to guarantee QoS for all subscribers. Therefore, it is important that a telecom operator can provide different QoSs for subscribers who are charged by different rates.

The QoS control in IMS/GPRS is realized by the Session-Based Local Policy (SBLP) functionality defined in 3GPP R5 [3GP05c]. The SBLP utilizes the Policy Decision Function (PDF; see Figure 9.6(d)) to make policy decisions based on session and media-related information obtained from the CSCF. In other words, the QoS policy is controlled by the PDF, where the policy rules can be formulated based on static information (such as the subscription profile), dynamic information, and the available resources. The combination of such policy rules, once met for a service request, can trigger a desired action (such as allowing the service with the requested bandwidth).

This policy rule framework allows the telecom operators to deploy service logic while optimally utilizing the network resources. Specifically, by configuring the policy stored in the PDF, telecom operators are able to implement the QoS policy control flexibly for different applications in various IP networks.

When the QoS policy control and the FBC functionalities described in Section 9.1 are used as separate mechanisms, it will increase the interworking cost between net-work nodes (e.g., GGSN and CSCF) and charging nodes (e.g., CRF and PDF) [Yan06].

Through the Policy and Charging Control (PCC) defined in 3GPP R7 [3GP07c], integ-ration of QoS policy and charging rules can be realized in the IMS network to reduce the signaling costs. In the PCC architecture (Figure 9.6), the SBLP and the FBC function-ality are utilized to integrate the QoS policy and charging control. In this architecture, the Policy Enforcement Function (PEF; Figure 9.6(b)) at the GGSN is responsible for QoS control of the IP service flows. According to the classification of a subscriber, the type of the application to be accessed by the subscriber, and the local control policy defined by the telecom operator, the IMS manages and controls the IP network resources (e.g., the allocated bandwidth) to the application and defines its priority. The process of IMS resource control is described as follows: During the setup of a session

Figure 9.6 PCC integration architecture for IMS service

described in Section 7.1, the UE (MS) requests the network for related media para-meters (such as codec, media type, and bandwidth) via the SDP contained in the SIP message. The AF/CSCF (Figure 9.6(f)) then forwards the SDP parameters to the PDF (Figure 9.6(d)) through the Gq interface [3GP07a]. The PDF controls the QoS policy by authorizing the related media parameters, according to the users’ media messages and the local policy. After authorization, the authorized media parameters are returned to the UE and the resources for setting up the transmission bearer are reserved. The PDF then forwards the related IP QoS control parameter to the PEF/GGSN through the Go interface. As a device that executes the QoS control policy, the GGSN analyzes the source and destination IP addresses, and then controls and filters the IP flow.

The Policy and Charging Enforcement Function (PCEF; Figure 9.6(a)) is implemen-ted in the GGSN. This function includes the TPF and the PEF. The Policy and Charging Rules Function (PCRF; Figure 9.6(c)) includes the CRF and the PDF (Figure 9.6(d)).

The PCRF makes policy decision and provides IMS charging rules to the PCEF. The QoS decision is based on charging-related information and the service information.

In this way, the charging rules are consistent with the QoS policy. According to the subscriber identity (e.g., IMSI), the PCRF can also request subscription information related to the bearer layer policies from the Subscription Profile Repository (SPR; see Figure 9.6(e)).

The AF hosts the service logic and communicates with the PCRF for the application level session information. This information indicates how to classify the service flows and to apply policy control at the GGSN. The offline and online charging systems (CDF and OCS; see Figure 9.6(g)) interact with PCEF for online credit control and the collection of offline charging information, respectively.

9.5 Concluding Remarks

In this chapter, we introduced the service data flow-based charging (FBC) architecture consisting of the Charging Rule Function (CRF), the Traffic Plane Function (TPF) and the Application Function (AF). The FBC allows breaking down of a PDP context into individual service data flows determined by the IP addresses and the port numbers.

Therefore, the mobile operators can efficiently meter data usage for individual service flows. The FBC solution is used to accurately classify and charge the data packets by their content types through static and dynamic policies. For example, all pack-ets addressed to a Domain Name Server (DNS) server are not accounted; all packpack-ets addressed to a service (identified by the IP address) are charged, and the IP-flows will appear in CDRs.

In the FBC architecture, the functionality of TPF/GGSN is enhanced to utilize IP packet filters such that different service flows within the same bearer session can be classified. This chapter gave GPRS and IMS service examples to explain how the FBC works. We also elaborated on the contents of the messages exchanged between the CRF and the AF, and between the CRF and the TPF.

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At the end of this chapter, we briefly described the integration of Policy and Char-ging Control (PCC) for UMTS R7 and R8. In this architecture, the PCRF is designated for the determination of the policy rules in real time. With this node, a set of policy rules can be activated to verify access permission, check and debit credit balance etc., all in real time. The PCRF enforces these policy rules through its interaction with the PCEF, which handles the GPRS transport plane. More details of the PCC can be found in [3GP07c].

Review Questions

1. How does a telecom operator charge the transferred data for IMS signaling and IMS media with different tariff plans in UMTS Release 5? What are the disadvantages of this solution?

2. Describe the FBC architecture. Why is the AF only required for the IMS services?

3. Show how FBC works without PDP context.

4. What are the functionalities for the charging rule function and the traffic plane function?

5. Describe the messages for the Gx interface. What are the differences between them and the messages in the Rf interface?

6. Describe the messages for the Rx interface. What are the differences between them and the messages in the Gx interface?

7. Give an example of the charging rule for the IMS video call scenario.

8. Give an online IMS call example such that IMS signaling and the IMS media are transferred in two PDP contexts.

9. Describe the policy and charging integration architecture in UMTS Release 7. What are the advantages of this architecture?

References

[3GP05a] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Services and Systems Aspects; Telecommunication management; Charging management;

Charging data description for the Packet Switched (PS) domain (Release 5), 3G TS 32.215 version 5.9.0 (2005-06), 2005.

[3GP05b] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Policy control over Go interface (Release 6), 3G TS 29.207 version 6.5.0 (2005-09), 2005.

[3GP05c] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Ser-vices and System Aspects; End-to-end Quality of Service (QoS) concept and architecture (Release 5), 3G TS 23.207 version 5.10.0 (2005-09), 2005.

[3GP06a] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Overall high level functionality and architecture impacts of flow based charging; Stage 2 (Release 6), 3G TS 23.125 version 6.8.0 (2006-03), 2006.

[3GP06b] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Charging rule provisioning over Gx interface (Release 6), 3G TS 29.210 version 6.7.0 (2006-12), 2006.

[3GP07a] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Policy control over Gq interface (Release 6), 3G TS 29.209 version 6.7.0 (2007-06), 2007.

[3GP07b] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Rx Interface and Rx/Gx signalling flows (Release 6), 3G TS 29.211 version 6.4.0 (2007-06), 2007.

[3GP07c] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Policy and charging control architecture (Release 7), 3G TS 23.203 version 7.5.0 (2007-12), 2007.

[Cou03] Courcoubetis C. and Weber, R., Pricing Communication Networks: Economics, Technology, and Modelling. John Wiley & Sons, Ltd., Chichester, UK, 2003.

[Fal00] Falkner, M., et al., An overview of pricing concepts for broadband IP networks, IEEE Communications Surveys & Tutorials, 2nd Quarter: 2–13, 2000.

[IET05a] IETF, Diameter Network Access Server Application. IETF RFC 4005, 2005.

[IET05b] IETF, Diameter Credit-Control Application. IETF RFC 4006, 2005.

[Kou04] Koutsopoulou, M., et al., Charging, accounting and billing management schemes in mobile telecommunication networks and the Internet, IEEE Communications Surveys & Tutorials, 6(1): 50–58, 2004.

[Wimax] WiMAX Forum (www.wimaxforum.org)

[Yan06] Yan, T., Integration of policy and charging control in the IMS, Communicate (Huawei), 25: 41–43, 2006.

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