Huawei Technologies

2005.10 8

Solution

NOV 2006 ˙ ISSUE 2541

By Tang Yan

How does the IMS provide differentiated services with application-based

E2E QoS? How to define a charging mode and policy control mode that

comply with market requirements in regards to charging? The answers

to these questions are of prime importance to carriers who wish to rid

themselves of the role of providing only an “information pipeline”.

NOV 2006 ˙ ISSUE 25

Solution

Huawei Technologies

NOV 2006 ˙ ISSUE 25 42

The Future Integration of Policyand Charging Control

s an integrated control platform at thenetwork layer that provides multimediaservices over IP bearer networks, theIMS should be able to manage IP flows,as well as help carriers to manage an

All-IP network. The management of IP flows isrepresented by QoS policy control and chargingcontrol.

Requirements of differentiated servicesWith a booming market for multimedia broadband

data services, carriers need to increase the value ofservices as well as provide differentiated services toattract more subscribers. For current broadband dataservices, subscribers are charged by monthly fee mode.In the early years when network resources are relativelyabundant, such a charging mode helps to attract moresubscribers. However, as the number of subscribersincreases exponentially and point-to-point (P2P)software becomes more prevalent, transmissionbroadband resources are becoming more limited. Inaddition, because the consumption pattern of networkresources varies considerably among subscribersgenerally charged the same flat rate, carriers are notable to guarantee QoS for all subscribers.

Therefore, carriers should apportion theconstruction cost and other expenses to individualbroadband data users. Furthermore, carriers shouldprovide different QoS for subscribers who are chargeddifferent rates. Carriers also need to guarantee the QoSof the bearer resources of services, and should providedifferentiated services, based on the QoS levels theyprovide to subscribers and the agreements they signwith the SPs. In this way, carriers can direct subscribersand SPs to services with a QoS guarantee.

Requirements of a dominant value chainWith the proliferation of internet services, the

number of broadband subscribers enjoying broadbandservices is increasing sharply. In the near future, thedominance of traditional voice services will besuperseded by broadband data services. So, what wouldconstitute a reasonable charging mode for broadbanddata service, and how can carriers avoid becoming acheap transmission pipeline for all SPs during thetransition process?

First of all, flow-based charging appears in the courseof competition between carriers and SPs for the valuechain. To charge according to contents, carriers firstneed to analyze the data packet sent to (or receivedfrom) subscribers, in order to identify and distinguish

Athe content type of such data as, audio, video, or text.Then the related information can be sent to the onlineand offline charging system, where subscribers arecharged a flexible rate, according to the contents oftheir data.

Carriers used to play a prominent role in the value-chainfor traditional voice services, and because they provided boththe network and all the services, carriers at their owndiscretion could determine how much to charge subscribers.However, with the participation of SPs and CPs, carriersfound that SPs and CPs benefited considerably from thedata service, while carriers only served as an "informationpipeline provider" for them. Therefore, it is important forcarriers to recapture the initiative when determining thecharging policy, the focus of which is content-based charging.The integration of a charging policy and QoS controlsupports the provision of more differentiated transmissionchannels for different SPs and CPs, which can help carrierstake the initiative in the whole value chain.

Requirements of cost reductionIn order to reduce cost and improve efficiency,

the structure of the network must be simple. Theintegration of policy and charging control reducesoperation expenditure (OPEX) and capitalexpenditure (CAPEX), by simplifying the networkstructure and requiring less maintenance staff andcost.

PCC: Integration of Policy andCharging Control in the IMS

The policy and charging control (PCC) structureis defined in 3GPP R7. Based on the flow based control(FBC) structure defined in 3GPP R6, the PCCstructure adopts the session-based local policy (SBLP)function. In this case, integration of the QoS policyand charging control is achieved.

QoS policy controlThe session-based QoS local policy control is

defined in 3GPP R5. According to differentapplications of subscribers, as well as the local controlpolicy defined by carriers, the IMS can control the IPnetwork resources occupied by a specific application.For example, the IMS can control and manage thebandwidth allocated to the application and define itspriority.

The process of resource control by the IMS is asfollows: During the setup of a session, user equipment(UE) requests to the network for related mediaparameters (such as codec, media type, and bandwidth),via the Session Description Protocol (SDP) containedin the Session Initiation Protocol (SIP).

Solution

NOV 2006 ˙ ISSUE 25

and Gx interface are integrated as the Gx+interface. Further, the SPR function isadded, which sends the subscriptioninformation to the PCRF through the Spinterface. The addition of the SPR functioncan enhance the ability of the PDF tocontrol the QoS. The PDF cannot onlyprovide service-based QoS control, but alsothe subscription information-based QoScontrol for some non-realtime services.

PCC-based integratedcontrol point in the IMS

Through the PCC, the integration ofQoS policy and charging rule can be realizedin the IMS network. The effect of suchintegration goes beyond the simple additionof the two (i.e. 1 + 1 > 2), and can fulfillcarriers’ need to meet the rapid developmentof multimedia data service.

As an enhanced QoS policy controlfunction, the PCC can implement the QoSpolicy control, not only according to theservice information, but also the chargingrate of the service flows, and the subscriptiondata obtained from the SPR such as, currentcell location of the subscriber, subscriberidentifier, IP address of the UE, QoSinformation, and subscriber group type.

In the PCC structure, the QoS decision isbased on charging related information, so thatthe charging rule is consistent with the QoSpolicy. By spending a little more, subscriberscan obtain better QoS. For example, a prepaidservice subscriber and a postpaid servicesubscriber will enjoy different QoS (such asin bandwidth and priority) when using real-time or non-real-time services. In addition,different charging rates will be adopted fordifferent time segments (such as during busyhours and non-busy hours), resulting invarious QoS policies.

The end-to-end IMS solution providedby Huawei adopts the PCC structure.Through the integration of QoS control andcharging rule, Huawei’s IMS solution canprovide flexible differentiated services forcarriers, which can help to improve thecompetitiveness of carriers, while at the sametime promoting the development of thewhole value chain along a correct path.

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The proxy-CSCF (P-CSCF) then forwardsthe SDP parameters to the policy decisionfunction (PDF), through the Gq interface.

The PDF then authorizes the relatedmedia parameters, according to the users’media messages and the local policy.

After authorization, the authorized mediaparameters are returned to the UE and theresources for setting up the transmissionbearer are reserved.

The PDF then forwards the related IPQoS control parameter to the GatewayGPRS Support Node (GGSN), through theGo interface.

As a device that executes the QoS controlpolicy, the GGSN analyzes the source anddestination IP addresses, and then controlsand filters the IP flow.

The QoS policy is controlled by thePDF. By configuring the policy stored inthe PDF, carriers are able to implementthe QoS policy control f lexibly fordifferent applications in various IPnetworks.

FBCThe FBC structure is defined in 3GPP

R6. The FBC structure solves the problemof charging at the bearer layer. The CDR atthe application layer is generated in theCSCF and related application servers. Gy/Gz is used to send charging data to bothonline and offline charging systems. Thecharging data include: session type, starttime, end time, and service flow information.

The process is as follows:The UE sends an SIP message to the

CSCF.The P-CSCF notifies the Charging Rule

Function (CRF) of the information relatedto the data flow by way of the Rx interface,including the IP flow identifier, bandwidth,and QoS type.

The CRF then sends the flow informationto the GGSN, including the IP flow detailand charging key (i.e. the charging rule).

The GGSN then sends data needed forcharging to the charging system, accordingto the charging key.

PCC integration solutionComparing the two structures mentioned

above, when policy control and FBC areused as two separate systems, they have theirown functional entities and interfaces.However, both their functional entitiesand the contents of the messages atthe interfaces are similar. Separation ofpolicy control and FBC will increase thecomplexity of the network structure andmessage flow (due to the interworking ofNEs such as GGSN, P-CSCF with entitieslike CRF and PDF), as well as worsen real-time performance and efficiency. Therefore,the CRF and PDF can be integrated intoone device, and the message interface canbe extended.

As shown in Fig.1, the PDF and CRFare integrated into one device which iscalled the PCRF. The Policy EnforcementPoint (PEP) and Traffic Plane Function(TPF) are realized in the GGSN. The Gqinterface and the Rx interface are integratedas the Rx+ interface, and the Go interface

Integration of Policy and Charging Control in the IMS

Editor: Pan Tao pantao@huawei.comFig. 1 PCC integration solution

Gx

Gz

Gy

PEP TPF

GGSN

Offline Charging System

Online Charging System

Rx

Sp

CRF PDF

Policy & Charging Rule Function (PCRF)

P-CSCF

SPR