Overview of ERPS

Definition

Ethernet Ring Protection Switching (ERPS) is a protocol defined by the International Telecommunication Union - Telecommunication Standardization Sector (ITU-T) to prevent loops at Layer 2. As the standard number is ITU-T G.8032/Y1344, ERPS is also called G.8032. ERPS defines Ring Auto Protection Switching (RAPS) Protocol Data Units (PDUs) and protection switching mechanisms. It can be used for communication between Huawei and non-Huawei devices on a ring network.

Related Concepts

ERPSv1 and ERPSv2 are currently available. ERPSv1 was released by the ITU-T in June 2008, and ERPSv2 was released by the ITU-T in August 2010. ERPSv2, fully compatible with ERPSv1, extends ERPSv1 functions. Table 1 compares ERPSv1 and ERPSv2.

**Table 1** Comparison between ERPSv1 and ERPSv2
Function	ERPSv1	ERPSv2
Ring type	Supports single rings only.	Supports single rings and multi-rings. A multi-ring topology comprises major rings and sub-rings.
Port role configuration	Supports the RPL owner port and ordinary ports.	Supports the RPL owner port, RPL neighbor port, and ordinary ports.
Topology change notification	Not supported.	Supported.
R-APS PDU transmission modes on sub-rings	Not supported.	Supported.
Revertive and non-revertive switching	Supports revertive switching by default and does not support non-revertive switching or switching mode configuration.	Supported.
Manual port blocking	Not supported.	Supports forced switch (FS) and manual switch (MS).

As ERPSv2 is fully compatible with ERPSv1, configuring ERPSv2 is recommended if all devices on an ERPS ring support both ERPSv1 and ERPSv2.

Purpose

Generally, redundant links are used on an Ethernet switching network to provide link backup and enhance network reliability. The use of redundant links, however, may produce loops, causing broadcast storms and rendering the MAC address table unstable. As a result, the communication quality deteriorates, and communication services may even be interrupted. To resolve these problems, ERPS can be used for loop avoidance purposes.

ERPS blocks the ring protection link (RPL) owner port to remove loops and unblocks it to promptly restore communication if a link fault occurs.

Table 2 compares various ring network protocols.

**Table 2** Ring network protocol comparison
Ring Network Protocol	Advantage	Disadvantage
ERPS	Fast convergence, meeting carrier-class reliability requirements. Is a standard ITU-T protocol that allows Huawei devices to communicate with non-Huawei devices. Supports single and multi-ring topologies in ERPSv2.	Requires complex manual configurations to perform functions.
STP/RSTP/MSTP	Applies to all Layer 2 networks. Is a standard IEEE protocol that allows Huawei devices to communicate with non-Huawei devices.	Slow to converge large-scale networks and fails to meet carrier-class reliability requirements.

Benefits

This feature offers the following benefits:

Protects services and prevents broadcast storms on ring networks.
Meets carrier-class reliability requirements for network convergence.
Allows communication between Huawei and non-Huawei devices on ring networks.