Public Network Traffic

Description

Public network traffic refers to traffic that is sent to or received from an NGN (Next Generation Network) for processing according to the normal rules of the NGN. In the context of 3GPP, this term is primarily used in specifications related to the IP Multimedia Subsystem (IMS), such as 22.519 and 24.229. Public network traffic is the standard type of traffic exchanged between IMS entities and external networks, adhering to the protocols and procedures defined for public networks. It contrasts with private network traffic, which may be subject to different rules or isolation.

The concept of public network traffic is important for understanding how IMS handles communication with external networks, including the PSTN, PLMN, and the Internet. When a user initiates a session, the traffic generated is classified as public network traffic if it is destined for processing according to normal NGN rules. This means that it follows standard routing, security, and QoS policies. The IMS core network elements, such as the Call Session Control Function (CSCF), Media Gateway Control Function (MGCF), and Media Gateway (MGW), process public network traffic to ensure interoperability with external networks.

In the IMS architecture, public network traffic is distinguished from traffic that may be subject to special handling, such as emergency calls or lawful interception. The classification of traffic as public network traffic allows the network to apply appropriate policies and ensure that resources are allocated correctly. For example, public network traffic may be subject to normal charging and policy control, while other types of traffic might have different treatment.

The definition of public network traffic has evolved over time. In earlier releases (Rel-8 to Rel-16), it was defined as traffic sent to the IM CN subsystem for processing according to normal rules of the NGN. In Release 17, the definition was revised to include traffic sent to or received from an NGN, reflecting a more bidirectional perspective. This change acknowledges that traffic can originate from the NGN as well as be sent to it, and it aligns with the evolving understanding of network interactions.

Public network traffic is a fundamental concept for ensuring that IMS can interoperate with a wide range of networks while maintaining security, QoS, and policy enforcement. It enables operators to manage traffic effectively and provide consistent services to users, regardless of the origin or destination of the traffic.

Purpose & Motivation

The concept of public network traffic was established to differentiate standard traffic within the IMS from other types of traffic that may require special handling. In the early days of IMS, it was necessary to define how traffic to and from external networks should be processed to ensure interoperability and consistent service delivery. Public network traffic represents the baseline for normal traffic, allowing operators to apply standard policies and procedures.

By defining public network traffic, 3GPP provided a clear framework for classifying traffic, which is essential for functions such as charging, policy control, and security. It helps network elements determine how to route and process packets, ensuring that public network traffic is handled according to the expected rules. This classification also aids in troubleshooting and network management, as it provides a common understanding of traffic types.

The evolution of the definition in Release 17 to include traffic received from an NGN reflects the growing complexity of network interactions and the need to consider bidirectional flows. This change ensures that the concept remains relevant as networks become more interconnected and services span multiple domains.