Ethernet Header Compression

Description

Ethernet Header Compression (EHC) is a protocol defined by 3GPP to efficiently transmit Ethernet frames over cellular radio access networks (RAN), specifically for NR (New Radio) and LTE. It operates by compressing the often-redundant fields within Ethernet frame headers before transmission over the Uu air interface between the User Equipment (UE) and the gNB (in 5G) or eNB (in LTE). The protocol is typically implemented in the Packet Data Convergence Protocol (PDCP) layer, which is responsible for header compression and ciphering. EHC works by establishing a context between the compressor (sender) and decompressor (receiver) for each data flow. This context contains static information about the Ethernet header fields, such as source and destination MAC addresses, VLAN tags, and EtherType. After an initial full header is sent to establish the context, subsequent packets transmit only a compressed header containing dynamic fields (like sequence numbers) and changes to static fields, significantly reducing the per-packet overhead.

The architecture involves EHC entities in both the UE and the base station (gNB/eNB). Compression and decompression are performed at the PDCP layer. The network configures EHC parameters via RRC (Radio Resource Control) signaling, specifying profiles and contexts. EHC supports multiple profiles to handle different Ethernet frame types, including those with and without VLAN tags. It uses robust header compression (ROHC) principles adapted for Ethernet, employing feedback mechanisms to ensure reliable context synchronization between compressor and decompressor, even in lossy radio conditions.

EHC's role is critical in the 5G system architecture for supporting Ethernet-based services that require low latency and high reliability, such as those defined for the 5G LAN-type service, industrial automation, and fronthaul/backhaul integration. By reducing header size, it decreases transmission time and increases effective data throughput, which is vital for meeting the stringent requirements of Ultra-Reliable Low-Latency Communication (URLLC) and enhanced Mobile Broadband (eMBB) use cases. It enables the 5G system to natively transport layer 2 Ethernet frames, facilitating integration with existing Ethernet-based industrial networks and supporting network slicing for isolated service segments.

Purpose & Motivation

EHC was introduced to address the inefficiency of transmitting standard Ethernet frames, which have a minimum header size of 14 bytes (plus optional VLAN tags), over the bandwidth-constrained and latency-sensitive air interface in 4G and 5G networks. Prior to EHC, transporting Ethernet traffic over cellular required tunneling protocols like GTP-U, which added further overhead, or transmitting uncompressed headers, wasting valuable radio resources. This was particularly problematic for new 5G use cases like industrial IoT, vehicle-to-everything (V2X), and mobile fronthaul, where many small, frequent Ethernet packets (e.g., for sensor data or control signals) are generated, making header overhead a significant portion of the total transmission.

The creation of EHC was motivated by the need to optimize radio resource utilization for Ethernet-based services, which are foundational in many vertical industries. 3GPP Release 16, which introduced enhanced support for vertical LAN services and time-sensitive networking, identified Ethernet transport as a key requirement. EHC directly supports these capabilities by minimizing air interface overhead, thereby improving spectral efficiency, reducing latency, and increasing capacity for Ethernet flows. It solves the problem of efficiently integrating layer 2 Ethernet networks with 3GPP cellular systems, enabling 5G to act as a seamless Ethernet bridge for industrial and enterprise applications.