IP Connectivity Access Network Session

Description

An IP-CAN session is a central concept in the 3GPP policy and charging control (PCC) architecture, defined in specifications such as TS 23.203, TS 29.061, TS 29.212, TS 29.213, TS 29.214, TS 29.215, and TS 32.251. It represents the association between a User Equipment (UE) and an IP network (PDN), identified by the UE's IP address(es) and UE identity information, if available. The IP-CAN session is the context within which one or more IP-CAN bearers are established, and it exists as long as the UE's IP addresses are assigned and announced to the IP network.

In the PCC architecture, the IP-CAN session is the point of policy control and charging for a UE's connectivity to a PDN. When a UE attaches to the network and establishes a PDN connection, an IP-CAN session is created. The PCRF (Policy and Charging Rules Function) or PCF (Policy Control Function) maintains session state and makes policy decisions based on subscription information, network policies, and service requirements. These decisions are communicated to the PCEF (Policy and Charging Enforcement Function) or SMF (Session Management Function) via the Gx or N7 interface.

The IP-CAN session can incorporate multiple IP-CAN bearers. The support for multiple bearers per session is IP-CAN specific; for example, in EPS, a PDN connection can have multiple EPS bearers (default and dedicated). The session aggregates the charging and policy information for all bearers, allowing the network to manage the overall connectivity for the UE. The session is identified by the UE's IP address(es) and, if available, additional UE identity information such as IMSI or access line identifier.

For fixed broadband access, the IP-CAN session can also be identified primarily by an IP address(es). In this context, the term UE corresponds to the device accessing the services (e.g., residential gateway, 3GPP UE, or fixed end-device), the PDN identifies the IP network where the device gets IP connectivity, and the UE identity information may be the IMSI, user-name, or access line identifier. In a Fixed Broadband Access, an IP-CAN session corresponds to a Subscriber IP Session as defined in TR-146.

The IP-CAN session is also used for charging purposes. The charging system generates charging data records (CDRs) per IP-CAN session, which can be correlated with the bearers within the session. This allows operators to charge based on the session's characteristics, such as the PDN connected to, the QoS of the bearers, and the volume of data transferred.

Overall, the IP-CAN session is a key abstraction that enables the core network to manage policy, QoS, and charging for a UE's IP connectivity in a technology-agnostic manner, supporting both 3GPP and non-3GPP access networks.

Purpose & Motivation

The IP-CAN session concept was introduced to provide a unified framework for managing policy, QoS, and charging for IP connectivity across different access technologies. Prior to its introduction, policy and charging were often handled at the access level, leading to fragmentation and inconsistent treatment of services. The IP-CAN session abstraction allows the core network to maintain a single context for a UE's IP connectivity, regardless of whether the access is via LTE, 5G, WLAN, or fixed broadband.

The primary motivation was to enable the deployment of advanced services that require end-to-end policy control and charging, such as IMS-based voice and video, and to support roaming and interworking between different networks. By defining a session that encompasses all bearers for a UE's PDN connection, the network can apply consistent policies and generate accurate charging records. This is essential for operators to monetize their services and to ensure a good user experience.

Furthermore, the IP-CAN session supports the evolution towards all-IP networks and the Internet of Things (IoT), where a vast number of devices require connectivity with varying QoS and charging requirements. The session concept scales to handle multiple devices and sessions, and it provides the necessary hooks for network slicing and edge computing in 5G and beyond.