Introduction

Quality of Services (QoS) is “the collective effect of service performance which determine the degree of satisfaction of a user of the service” according to ITU-T E.800 Recommendation. QoS control in an IP based network involves the following steps. Step 1 is to provide service definition in terms of the service level agreement (SLA) with the users. The SLA defines service session characteristics, QoS agreement etc. Step 2 is to map SLA to network key performance indicators (KPIs) such as delay, jitter, packet loss, and bandwidth etc. Step 3 is to map network KPIs to QoS parameters in the transport control devices and to execute the transport controls in the devices. Therefore, QoS involves the entire network operational processes, from service provision to network engineering to charges based on the QoS provided. In a converged IMS network, that translates to the OSS and BSS for service provision and charging; service delivery platform for service creation; session control elements, such as CSCF, HSS for session mediation and control; transport equipment such as GGSN in mobile network, BRAS in fixed network for policy enforcement. QoS has been a studying topic ever since the invention of IP network because of the dynamic nature of the IP network. The studies carried out by a number of standard organizations, such as 3GPP, 3GPP2, TISPAN and WiMAX Forum have been focused on specific network architectures, such as UMTS mobile network, fixed network, CDMA network and WiMAX network etc although the solutions have a lot in common. With many operators moving toward the converged networks, fixed-mobile convergence (FMC) is gradually becoming a reality. An increasing application scenarios demand the converged QoS solutions, such as video application transferring between IPTV and mobile TV, and VoIP call transferring between fixed broadband network and mobile broadband network etc. Converged QoS solutions provide great benefits to meet the ever increasing IP applications and to truly realize the access agnostic experiences the end users expect. In the following sections, we provide reviews of the QoS architectures for mobile and fixed networks and present a converged QoS solution that meets both the fixed and mobile network requirements.

QoS architectures for mobile and fixed networks

The Policy and Charging Control (PCC) architecture defined by 3GPP has been recognized as the de-factor standard for mobile network QoS solutions. The PCC architecture provides gating control and QoS control such as service authorization, QoS conflict handling and policy control for both subscriber and network initiated services. The QoS control can be applied onto service data flow level or IP-CAN bearer level. Besides of the QoS functions, PCC provides charging functions, such as charging rules, charging types (volume based charging; time based charging; volume and time based charging; event based charging etc.) as well as charging correlation. The PCC architecture however does not provide coverage for fixed network.

The Resource and Admission Control subsystem (RACS) architecture defined by TISPAN has been recognized as the de-factor standard for fixed network QoS solutions. The RACS provides both topology-aware and topology-hiding functions besides the gating control and QoS functions for fixed network access nodes, such as Broadband Remote Access Server (BRAS) and border gateways. RACS specifies only limited offline charging functions.

QoS solutions for converged network

There are a number of business drivers for the converged QoS solutions:

1. The evolution of converged all IP core network, such as IP Multimedia Subsystem (IMS), leads toward to the elimination of boundaries between mobile and fixed networks and provides a driving force for converged QoS solutions.

2. Increasing numbers of operators are moving toward to own both fixed and mobile networks. With the relaxing regulations and fierce competition in many regions of the world, there are increased consolidations among fixed and mobile operators. Converged QoS solutions have become necessities for these operators to harmonize the QoS experiences for the subscribers that use both fixed and mobile services.

3. There are more and more converged applications spanning cross fixed and mobile domains during an application session. For instance, an IPTV viewer may decide to handover the program he is watching to his mobile TV handset so he can still enjoy the program outside of his home. The QoS he subscribes will need to be coordinated between the fixed and mobile networks serving him.

ZTE’s Resource Control Platform (ZXUN RCP) is designed to meet the converged QoS demands. The RCP architecture is illustrated in figure 1 below.

Figure 1: Architecture of ZTE’s converged QoS solution

In the above architecture, ZXUN RCP includes the functions of ETSI TISPAN RACS (i.e. A-RACF and SPDF), PCRF defined in 3GPP PCC architecture and PDF (Policy Distribution Function) defined in WiMAX Forum. So it can control different kinds of access networks, including UMTS, CDMA2000, WiMAX and fixed broadband.

ZXUN RCP receives the request for resource and charging policies of a specific service flow which is identified by the bearer layer equipment through DPI (Deep Packet Inspection). ZXUN RCP installs the resource and charging policies for the service to bearer layer equipment. Usually the bearer layer equipment controlled by ZXUN RCP includes GGSN, AGW/HA, PDSN, BRAS, Border gateways, etc.

ZXUN RCP also performs QoS authorization for service request from AFs (Application Function) (such as, P-CSCF, AGCF in IMS network, or other non IMS elements), and it installs the policies (such as authorized bandwidth) for the service flow to bearer layer equipment. Bearer layer equipment detects the flow and implements the policies accordingly.

ZXUN RCP gets the subscriber related service profile (e.g. Service QoS profile) from SPR (Subscription Profile Repository) which can be co-located with common user data base, such as HSS, AAA server etc.

By employing ZTE’s unified All-IP hardware platform, the RCP provides the benefits of low cost, flexible networking, easy interworking, smooth migration, easy expansion, large capacity and high reliability to both large and small operators.

Conclusions

With the increasing bandwidth provided by both fixed and mobile networks, and the increasing applications of fixed-mobile convergence, there are growing demands requiring converged QoS control for both fixed and mobile networks. ZTE’s QoS solution can meet the QoS requirements of different access technologies as well as future core technologies such as IMS core and Evolved Packet Core (EPC). Besides the converged QoS control, the platform provides a variety of charging mechanisms. RCP is part of ZTE’s end to end solutions to serve the world-wide operators for better network performances and better end-user experiences.