Multi Access PDN Connectivity

Description

Multi Access PDN Connectivity (MAPCON) is a 3GPP feature standardized in Release 10 and later, which enables a User Equipment (UE) to establish and maintain multiple simultaneous Packet Data Network (PDN) connections to the same Access Point Name (APN) across different 3GPP and non-3GPP radio access networks. This is distinct from having separate PDN connections to different APNs; MAPCON specifically allows connectivity to a single APN (like "internet" or "ims") over multiple accesses, such as LTE and Wi-Fi, at the same time. The feature operates within the Evolved Packet Core (EPC) architecture, involving key network elements like the Packet Data Network Gateway (PGW), Serving Gateway (SGW) for 3GPP access, and evolved Packet Data Gateway (ePDG) for untrusted non-3GPP access.

Architecturally, MAPCON relies on the PGW acting as the common anchor point for the PDN connection across all accesses. The UE initiates a PDN connection over a primary access (e.g., LTE) to a specific APN via the PGW. Subsequently, the UE can establish an additional PDN connection to the same APN over a secondary access (e.g., Wi-Fi), which is anchored at the same PGW. The PGW manages these as separate bearer contexts (or PDN connections) but associates them as belonging to the same UE and APN. The UE is assigned the same IPv4 address and/or IPv6 prefix for the PDN connection on both accesses, or it can be assigned different IP addresses depending on operator policy and network configuration. The PGW maintains separate GTP (GPRS Tunneling Protocol) tunnels or PMIP (Proxy Mobile IP) bindings for each access, converging at the PGW.

How MAPCON works involves coordination between the UE and the network. The UE indicates its support for MAPCON during attachment or PDN connectivity procedures. The network (MME for 3GPP access, ePDG for non-3GPP access) informs the PGW that the new PDN connection request is for an APN to which the UE already has an active connection on another access. The PGW then correlates the requests and establishes the additional context. From a traffic flow perspective, the UE can have IP traffic routed over either access based on UE policies, network policies, or application preferences. This enables use cases like offloading bulk data traffic to Wi-Fi while keeping latency-sensitive IMS signaling on LTE. The feature is closely related to ANDSF (Access Network Discovery and Selection Function), which can provide the UE with policies for access selection between these concurrent connections.

Purpose & Motivation

MAPCON was introduced to address the growing need for devices to leverage multiple available radio access technologies simultaneously, improving user experience and network efficiency. Prior to MAPCON, a UE could be connected to multiple PDNs, but each PDN connection was tied to a single access type at a time. If a UE switched from LTE to Wi-Fi for a given APN, the PDN connection on LTE would be torn down before establishing it on Wi-Fi, causing service interruption. This limitation was problematic as operators deployed Wi-Fi hotspots and sought to use them for data offloading without disrupting ongoing services.

The primary motivation was to enable seamless access network utilization and traffic steering without breaking the PDN connectivity session. For example, a user could start a video stream over LTE and then move into Wi-Fi coverage; with MAPCON, the video session could be seamlessly handed over to Wi-Fi (or even use both links concurrently for aggregation) without re-establishing the IP session. This is crucial for services requiring persistent IP addresses, like VPNs or certain IMS applications. It also allows operators to implement intelligent traffic management policies, directing specific traffic flows (e.g., best-effort Internet) to Wi-Fi while keeping mission-critical signaling on the 3GPP network.

MAPCON laid the groundwork for more advanced multi-access capabilities in later releases, such as IP Flow Mobility (IFOM) and non-seamless WLAN offload. It represented a shift from access-specific PDN connections to access-agnostic PDN connectivity, aligning with the vision of a unified core network (EPC) that treats 3GPP and non-3GPP accesses as equal. This was a key step towards true network convergence and the ability to deliver consistent services across heterogeneous access networks.