IP-Connectivity Access Network

Description

The IP-Connectivity Access Network (IP-CAN) is not a single physical network element but a logical architectural concept defined within the 3GPP framework. It represents the entire set of network entities and functions that collectively establish and maintain IP bearer connectivity for a user. This connectivity originates at the User Equipment (UE) and traverses the radio access network (e.g., UTRAN, E-UTRAN, NG-RAN) and the core network (e.g., GPRS core, EPC, 5GC) to reach a Packet Data Network (PDN) Gateway (PGW) in 4G or a User Plane Function (UPF) in 5G, which serves as the anchor point to external IP networks.

From a functional perspective, the IP-CAN encompasses all layers and protocols involved in the IP session. This includes the establishment, modification, and termination of bearers or QoS Flows that carry the user's IP traffic. Each IP-CAN session is associated with a specific UE IP address and is uniquely identified for the purposes of policy and charging control. The architecture is designed to be access-agnostic in later releases, meaning the core policy logic can apply uniformly whether the UE is connected via 3G, 4G, 5G, or non-3GPP access like Wi-Fi.

The IP-CAN's primary role is to serve as the context for the Policy and Charging Control (PCC) architecture. The Policy and Charging Rules Function (PCRF) or the Policy Control Function (PCF) in 5GC uses the IP-CAN session as a key anchor point for applying policy decisions. The PCRF/PCF receives information about the IP-CAN session (e.g., IP address, access type, default bearer characteristics) from the network element acting as the Policy and Charging Enforcement Function (PCEF), typically the PGW or UPF. Based on subscriber profiles, service requests, and network conditions, the PCRF/PCF then installs dynamic PCC rules into the PCEF. These rules govern QoS parameters (like guaranteed bitrate), gating (allowing/blocking packets), and charging methods for specific service data flows within the IP-CAN session.

Key components involved in realizing an IP-CAN session include the UE, the radio access network, the serving gateway (SGW) in EPC, the PGW/UPF (which acts as the IP-CAN bearer termination point and the PCEF), and the PCRF/PCF. The interfaces between these elements, such as the Gx interface (between PCRF and PGW) or the N7 interface (between PCF and SMF), are used to manage the IP-CAN session's policies. The concept is fundamental to enabling seamless, quality-assured, and billable IP multimedia services across evolving network generations.

Purpose & Motivation

The IP-CAN concept was introduced to provide a standardized, abstract model for IP connectivity within 3GPP networks, which was essential as networks evolved from circuit-switched voice to all-IP architectures supporting rich multimedia services. Prior to its formalization, managing QoS and charging for diverse IP services was complex and often proprietary. The IP-CAN model created a clear demarcation point and a consistent session context, enabling the development of a unified Policy and Charging Control (PCC) framework.

Its creation solved the critical problem of how to dynamically apply network policies (for quality of service, traffic gating, and charging) to a user's IP session, regardless of the underlying access technology. By defining the IP-CAN session, operators could correlate a user's service usage (e.g., a video stream) with their network connection, allowing for service-aware charging (like zero-rating) and guaranteed bandwidth for premium services. This was a key enabler for the IP Multimedia Subsystem (IMS) and commercial data service plans.

Furthermore, the IP-CAN abstraction future-proofed the policy architecture. As new access technologies emerged (like LTE and later 5G NR), the core PCC logic could remain largely unchanged by simply updating the definition of the IP-CAN session parameters for that new access type. This allowed for smooth evolution from 3G to 4G and 5G while maintaining consistent service and business logic for operators.