LTE-M Architecture: User and Control Plane Explained

This article explains the basics of LTE-M architecture, describing both the user plane and control plane.

Introduction

LTE-M adheres to 3GPP specifications, similar to standard LTE technology.

LTE-M stands for Long Term Evolution for Machine-Type Communications. It’s primarily designed to meet the needs of cellular IoT devices, such as low cost, deep coverage, extended battery life, and high cell capacity. Different categories of LTE-M devices exist, including Cat-0, Cat-M1, and Cat-M2, as defined in various 3GPP releases. Specifically, LTE-M Cat-0, Cat-M1, and Cat-M2 follow 3GPP TS 36 series of rel.12, rel.13, and rel.14 respectively.

Let’s delve into the components of the LTE-M architecture.

As shown in the figure, LTE SAE (System Architecture Evolution) consists of the User Equipment (UE), evolved NodeB (eNodeB), and Evolved Packet Core (EPC). Interfaces between these entities include Uu (between UE and eNodeB), X2 (between two eNodeBs), and S1 (between EPC and eNodeB). The eNodeB encompasses the functionalities of both the Radio Network Controller (RNC) and NodeB from the previous UMTS architecture. LTE is a completely IP-based network. The basic architecture contains the following network elements:

1. LTE EUTRAN (Evolved Universal Terrestrial Radio)
2. LTE Evolved Packet Core.

The figure above illustrates the LTE-M architecture in a roaming scenario. Both the user plane and control plane are depicted, which are used for the transport of data and control information.

There are two main Network Attach options to support connectivity:

1. Attach with Packet Data Network (PDN) connection: This is the standard method for connecting to the network and accessing data services.
2. Attach without PDN connection: This option was added in 3GPP Release-13 to allow UEs offering CIoT (Cellular Internet of Things) optimizations to remain attached without a PDN connection. This is useful for devices that only need to exchange small amounts of data or are primarily used for control signaling.

There are different data connectivity options for PDN connections available to IoT devices using the EPS:

• IP over Control Plane
• IP over User Plane
• Non-IP over Control Plane
• Non-IP over User Plane