Non-Seamless Wireless Offload

Description

Non-Seamless Wireless Offload (NSWO) is a network capability that allows a User Equipment (UE) to route selected IP traffic directly to a local data network via the radio access network, without tunneling it through the mobile operator's core network packet gateway (e.g., PGW in EPC, UPF in 5GC). The term 'non-seamless' indicates that this offloaded traffic does not benefit from mobility support or other core network services like charging, policy control, or seamless handover to other access types. The traffic is essentially treated as best-effort internet access provided directly by the access point. In 3GPP architectures, NSWO is supported over trusted non-3GPP access (like Wi-Fi) integrated with the core network, and also defined for 3GPP radio access.

Architecturally, for EPC, when a UE connects via a trusted non-3GPP access (like a carrier Wi-Fi network), it establishes an IP connection with the evolved Packet Data Gateway (ePDG) or directly with the access point. For traffic designated for NSWO, the UE requests a separate connection or uses a specific routing rule. The access point, based on policies received from the core network (AAA server, PCRF), identifies NSWO traffic (e.g., based on Destination-Based Packet Filters) and forwards it directly to the local network, bypassing the S2a/S2b interface towards the PGW. In 5GC, the concept is extended with the Non-3GPP InterWorking Function (N3IWF) for untrusted access and trusted non-3GPP access. The UE can establish a PDU session for NSWO, which is anchored locally at the access point/N3IWF and not in a UPF in the core data network.

The operation relies on policy control. The core network provides the UE and the access point with NSWO policies, often defined as ANDSF (Access Network Discovery and Selection Function) rules in EPC or UE Route Selection Policy (URSP) in 5GC. These policies specify which Application IDs or IP flows should be routed to the NSWO connection. The UE's IP stack implements IP flow mobility (IFOM) or multi-access PDU connectivity (MAPCON) principles to split traffic between the core-anchored PDN connection/PDU session and the NSWO connection. A key component is the ability to assign a separate IPv4 address and/or IPv6 prefix to the UE for the NSWO connection, distinct from its core network assigned IP address. This ensures traffic separation. NSWO is transparent to the end-user application, which simply uses the IP stack, while the network layers handle the routing decision.

Purpose & Motivation

NSWO was developed to address the growing congestion in mobile core networks caused by the exponential increase in data traffic, particularly from internet services like video streaming and web browsing. Offloading such traffic locally reduces the load on the core network gateways and backhaul links, leading to cost savings for operators and potentially better performance for users accessing local content. It solves the problem of inefficiently routing all traffic through a centralized gateway when a direct local path is available and sufficient, especially for traffic that does not require operator-specific services like IMS voice or guaranteed QoS.

The motivation stemmed from the proliferation of integrated Wi-Fi and cellular networks. Operators wanted to leverage their deployed Wi-Fi hotspots not just as an alternative access, but as a true traffic offload tool. Prior to NSWO, offload mechanisms often required tunneling all traffic back to the core (seamless offload), which did not alleviate core network load. NSWO provided a 'breakout' function. It also addresses latency-sensitive applications by providing a shorter path to local services or the internet, bypassing potential bottlenecks in the core network.

Historically, NSWO was standardized in 3GPP Release 11 as part of the work on Wi-Fi integration. It represented a shift from viewing non-3GPP access as merely an alternative to seeing it as a complementary resource for traffic management. It allowed operators to implement 'traffic steering' policies more granularly. Over subsequent releases, its policy control mechanisms evolved from ANDSF to more integrated policy frameworks in 5GC. NSWO remains relevant in 5G for offloading traffic from Fixed Wireless Access (FWA) or enterprise deployments where local internet breakout is desired, supporting the 5G design principle of distributed user plane functions and local area data networks (LADNs).