IP Mobility management Selection

Description

IP Mobility management Selection (IPMS) is a critical decision-making function within the 3GPP Evolved Packet Core (EPC) architecture, specifically defined for scenarios involving mobility between 3GPP and trusted or untrusted non-3GPP access networks. Its primary role is to determine the most suitable IP mobility management protocol for a User Equipment (UE) to maintain session continuity. This selection is not arbitrary; it is governed by a combination of static operator policies configured in the network and dynamic information such as the UE's reported capabilities and the type of access network it is currently using or attempting to attach to. The IPMS function typically resides within the network's policy control architecture, often associated with the Policy and Charging Rules Function (PCRF) or a dedicated selection function, which evaluates the input parameters against a set of predefined rules.

The operational workflow of IPMS is triggered during key mobility events, such as initial attachment, handover procedures, or when a UE registers over a new access type. The process begins with the network node (e.g., an Access Network Discovery and Selection Function (ANDSF) or the network gateway) receiving the UE's attachment request, which includes indicators of its supported mobility protocols (e.g., Dual-Stack Mobile IPv6 (DSMIPv6) client support, or support for network-based mobility like Proxy Mobile IPv6 (PMIPv6)). Simultaneously, the IPMS function consults the subscriber's profile and operator policies, which are pre-configured to reflect the network's strategic preferences—for instance, prioritizing network-based mobility to reduce UE complexity and battery consumption, or mandating client-based mobility for certain service types or roaming agreements.

Based on this evaluation, IPMS outputs a binding decision that instructs the relevant network entities—primarily the Packet Data Network Gateway (PGW) in EPC or the corresponding gateway in non-3GPP access—on which mobility mechanism to establish for that UE's IP session. For example, if the policy dictates and the UE supports it, the network may set up a PMIPv6 tunnel between the Serving Gateway (SGW) and the PGW, or a DSMIPv6 tunnel directly from the UE to the Home Agent (HA). This decision directly impacts the data path architecture and the signaling procedures for subsequent handovers. By centralizing this logic, IPMS provides a flexible and policy-driven framework that allows operators to deploy heterogeneous networks efficiently, manage different UE generations, and optimize network resources and performance without requiring changes on every single UE.

Purpose & Motivation

IPMS was introduced to address the growing complexity of mobile networks evolving beyond pure 3GPP radio access. With the inclusion of Wi-Fi (as a trusted or untrusted non-3GPP access) and later other radio technologies into the 3GPP system architecture, a standardized mechanism was needed to manage how a UE's IP session is maintained across these heterogeneous access types. Prior to its specification, mobility management was largely implicit or tied to a single protocol, which was insufficient for a multi-access environment where different UEs have varying capabilities and where operators might have different strategic or technical preferences for different scenarios (e.g., home network vs. roaming).

The creation of IPMS solved the problem of how to seamlessly integrate diverse IP mobility protocols—specifically client-based DSMIPv6 and network-based PMIPv6—under a unified policy framework. Without IPMS, the network would lack a deterministic way to select the appropriate mobility anchor and tunneling mechanism, potentially leading to compatibility issues, failed handovers, or suboptimal resource utilization. Its purpose is to decouple the UE's capability from the network's policy, giving operators control over mobility management strategy. This enables efficient network deployment, supports the gradual introduction of new mobility protocols, and is fundamental to realizing the 'Access Agnostic' vision of the Evolved Packet System (EPS), where core network services are delivered consistently regardless of the underlying radio technology.