Packet Switched Based Services

Description

Packet Switched (PS) based services is a term used in the context of WLAN interworking to describe services provided by a Public Land Mobile Network (PLMN) using IP bearer capabilities between WLAN UEs and the PLMN. This concept was introduced in Release 2 and evolved through Release 12. It encompasses all services offered by the 3G PS domain that utilize IP bearer services, including IMS, Internet access, Corporate IP network access, and other services like SMS and LCS. The term is specifically tied to scenarios where WLAN 3GPP IP Access is used, meaning the UE connects to the PLMN via a WLAN access network, and the PLMN provides IP connectivity.

The architecture for PS based services involves the interworking between WLAN and 3GPP networks. The WLAN UE connects to a WLAN access point, which then connects to the PLMN's Packet Data Gateway (PDG) or similar entity. The PDG acts as the gateway for IP traffic between the WLAN and the PLMN's packet core. The PLMN then provides IP bearer services, allowing the UE to access various PS services. The key components include the WLAN UE, WLAN access network, PDG, and the PLMN's PS domain (e.g., SGSN, GGSN in 3G). The services are delivered over IP, leveraging the PS domain's capabilities.

The definition of PS based services has evolved over releases. In early releases (Rel-2), it referred to services in scenario 3 and upwards, which involved WLAN 3GPP IP Access. The wording changed in Rel-6 to specify "when WLAN 3GPP IP Access is used" instead of "in scenario 3 and upwards." In Rel-7, the definition was reworded to a more general statement, removing the specific mention of WLAN interworking and focusing on the services themselves. In Rel-8, the definition reverted to the Rel-6 style, mentioning scenario 3 and upwards again. Subsequent releases (Rel-9 to Rel-12) kept this wording with minor punctuation changes. These changes reflect the ongoing refinement of the terminology as WLAN interworking evolved.

PS based services are important because they allow mobile operators to extend their service offerings over WLAN access, providing seamless connectivity and service continuity. This enables users to access the same services (e.g., IMS, Internet) whether they are on cellular or WLAN. It also allows operators to offload traffic from cellular networks to WLAN, reducing congestion. The term is part of the broader effort to integrate non-3GPP access technologies into the 3GPP ecosystem, which continues with 5G and beyond.

In practice, PS based services rely on the IP bearer capability provided by the PLMN. The UE must establish a connection to the PLMN via WLAN, which involves authentication, authorization, and tunnel establishment (e.g., IPsec). Once connected, the UE can access any IP-based service. The quality of service (QoS) may be managed by the PLMN to ensure appropriate treatment. Security is provided through encryption and authentication mechanisms defined in 3GPP specifications.

Overall, PS based services represent an early but foundational step towards fixed-mobile convergence and the integration of heterogeneous access networks. While the term is less prominent in 5G, its principles live on in the concept of access traffic steering, switching, and splitting (ATSSS) and other interworking features.

Purpose & Motivation

PS based services were created to enable mobile operators to provide their packet-switched services over WLAN access networks, extending coverage and capacity. Before this, cellular services were limited to 3GPP access, and WLAN was a separate, non-integrated network. The motivation was to allow users to seamlessly access services like IMS, Internet, and corporate networks via WLAN, while maintaining the operator's control and service continuity.

The term addressed the need for a standardized way to describe the set of services available when a UE connects to the PLMN via WLAN. It provided a common vocabulary for operators, vendors, and standards bodies. The evolution of the definition reflects the maturation of WLAN interworking, from early scenarios to more integrated approaches.

By offering PS based services, operators could offload traffic from congested cellular networks, improve user experience in indoor environments, and compete with fixed broadband providers. It also paved the way for more advanced interworking features in later releases, such as seamless offloading and multi-access connectivity.