LMA Address

Description

The LMA Address (LMAA) is a fundamental network identifier within the 3GPP Proxy Mobile IPv6 (PMIPv6) architecture. It is defined as the IP address of the Local Mobility Anchor (LMA) entity. This address serves multiple critical roles in both the control plane and user plane operations of network-based mobility management. In the control plane, the LMAA is the destination IP address to which the Mobility Access Gateway (MAG) sends its Proxy Binding Update (PBU) messages. These messages are used to register the UE's current point of attachment (the MAG's Proxy Care-of Address) with the LMA and to request IP prefix(es) for the UE. Conversely, the LMA sends Proxy Binding Acknowledgement (PBA) messages from this LMAA back to the MAG.

In the user plane, the LMAA acts as one endpoint of the bidirectional tunnel established between the LMA and the MAG for transporting the UE's data traffic. All downlink packets destined for the UE's Home Network Prefix are first routed to the LMA (specifically, to the LMAA). The LMA then encapsulates these packets, using the LMAA as the outer header source address, and tunnels them to the MAG's Proxy Care-of Address (Proxy-CoA). The MAG decapsulates the packets and forwards them to the UE. For uplink traffic, the MAG encapsulates packets originating from the UE and sends them to the LMAA, where the LMA decapsulates them and routes them toward the external packet data network. The LMAA is therefore central to the routing of all traffic for UEs attached via PMIPv6.

The LMAA is typically a stable, reachable IP address within the operator's core network. It can be an IPv6 address, an IPv4 address, or both, depending on the IP capabilities of the network and the tunnel protocol in use (e.g., IPv6-in-IPv6, IPv4-in-IPv4, or IPv4-in-IPv6). The specific LMAA to be used for a UE's session is determined during the initial attachment procedure, often communicated from the AAA infrastructure (HSS/3GPP AAA Server) to the MAG as part of the authentication and authorization process. The MAG then uses this address for all subsequent PMIPv6 signaling and tunnel establishment with that LMA instance. The concept of the LMAA ensures that the MAG has a definitive, routable destination for managing the mobility session.

Purpose & Motivation

The LMAA exists to provide a concrete, routable network locator for the LMA function, which is an abstract logical entity. In any IP-based communication, a destination address is mandatory for establishing connections and routing packets. The PMIPv6 protocol, upon which the LMA/MAG interaction is built, is an IP-based signaling protocol. Therefore, a standardized way to identify and address the LMA was necessary for interoperability.

Before the formal definition of the LMAA parameter, the address of the LMA would have been an implementation-specific detail, making multi-vendor interoperability difficult. By standardizing it as the 'LMAA' within 3GPP specifications (particularly TS 29.275), it ensures that all MAG implementations know which parameter carries the LMA's IP address during session establishment (e.g., from AAA attributes). This clear identification solves the problem of how a MAG, which may be in a different administrative domain or from a different vendor, discovers and communicates with the correct LMA for a specific subscriber. It is a key enabler for the decomposed, interoperable architecture of EPC-based non-3GPP access, ensuring reliable control plane signaling and user plane tunneling.

Key Features

• Serves as the destination IP address for Proxy Binding Update (PBU) control messages from the MAG
• Acts as the source IP address for the LMA-side of the user plane tunnel to the MAG
• Can be an IPv4 address, IPv6 address, or both (dual-stack support)
• Typically communicated to the MAG via AAA protocols during UE authentication
• Essential for routing downlink user data packets to the correct LMA instance
• A key parameter in the Binding Cache Entry (BCE) maintained by the LMA

Evolution Across Releases

Defining Specifications