With the development of Internet Multimedia Services (IMS), the challenge of defining how the IMS infrastructure would deliver application services and control the user experience was answered with Policy. Policy is simply the application of business rules to define how a subscriber interacts with the network, application and services. Since 3GPP included Policy into the IMS standards,(3GPP TS 23.203) the market has viewed Policy as simply bandwidth management and subscriber tiered services. However, this view of Policy is limited and incomplete implementation of Policy in a Communication Service Provider (CSP) network.
In order to truly implement a comprehensive policy architecture, policy must be integrated into the design and implementation of all network services. Creating rules to define how a subscriber connects to the network, authenticates, has an IP address allocated, along with all the interactions of network support services such as IPv6 translations, DNS, NAT, security services, etc. This Policy definition is the only way to truly define the subscriber interaction with services and applications.
As CSP’s transition to all IP networks, maintaining the Quality of Experience (QoE) will determine the CSP’s success against competition. The ultimate challenge in transitioning to these technologies is still providing at least the same QoE as the previous networks (3G and traditional circuit switched voice) across all services. Since voice is still the largest impact on ARPU, delivering a quality VOIP solution (or VoLTE for wireless 4G) that is as stable and reliable as circuit switched voice is essential for success. Comprehensive policy across all IP services in the network provides a level of management related to these new technologies and the subscriber experience.
IMS standards for Policy, specifically Policy defined at the Policy Control and Revenue Function’s (PCRF) relationship with the Policy Control Enforcement Function (PCEF), takes the first step in defining this policy architecture. The PCRF, by definition, defines the policy associated with the subscriber and sends policy updates to the PCEF, which will packet, shape (via Quality of Service (QoS)) the packet for that session. The PCRF makes these decisions based upon the subscriber’s tier of service, network origin, application, service definition and network status information. This Policy step is crucial, but it is incomplete for Comprehensive Policy across the network.
For Comprehensive Policy, all network services need to be Policy aware and be able to enforce policy according to the specific network service. For example, as a device connecting to the IMS network, a DNS query is sent to determine the Call Session Control Function (CSCF) for the first SIP request. A standard DNS server will simply return the A or AAAA record (depending of if this is on an IPv4 network or IPv6 network) that it has for the appropriate CSCF. However, Policy can be used to define how that DNS server can determine which CSCF is returned based upon the network and subscriber. By defining this first interaction, the most available CSCF address can be returned to the device or, more specifically, a CSCF scheme can be defined based upon the location, network status, and subscriber. This is the first step in defining the experience that subscriber has with the IMS service.
By defining Policy at the network services, the CSP takes control of the subscribers interaction at every point on the network. This makes all the network services a Policy enforcement point of the CSP’s business plan. These policies can be either dynamic or static, depending on the service or technology being deployed. Dynamic Policy allows for changes in the policy within the session without having dropping the session to make this Policy change. Static Policy is simply rules defined that do not change in mid-session. To provide for dynamic policy, a policy decision point is needed to pass policy changes to the policy enforcement point, this is the scheme that the PCRF and PCEF use to provide dynamic policy. However, using a combination of static and dynamic policy across all network services is the only way to offer comprehensive policy.
As CSP technologies, applications and services evolve, the real challenge is maintaining ARPU and reducing, or managing, subscriber churn in order to maximize profit and stay competitive. The only way to achieve this is to maintain, and improve, the QoE as new applications and services are delivered to the subscriber. Understanding and managing the relationships between all services and the subscriber with the network is the only way to control the QoE. Comprehensive Policy across all network elements and services is the only way to manage these relationships between the subscriber and services.