What is IEEE802.1CB?

Introduction

TSN (Time Sensitive Network) adopts the IEEE802.1CB (Frame Replication and Elimination for Reliability) standard, which defines redundancy mechanisms to improve network fault tolerance. This column provides an overview of IEEE802.1CB.

What is 802.1CB?

802.1CB is an IEEE 802.1 standard related to Ethernet networking that improves fault tolerance by duplicating Ethernet FRAMES at the source and sending them over multiple paths toward the destination.

The Need for 802.1CB

Ethernet FRAMES can be lost along the route from the sender to the destination due to CABLES disconnections or relay device failures. 802.1CB replicates Ethernet FRAMES at the sender and sends them over multiple routes, so even if a problem occurs on one route, the frames can reach the destination via other routes, preventing the loss of Ethernet FRAMES.
If multiple duplicate FRAMES are received at the destination, any frames received after the first one will be discarded. See Figures 1 and 2 for details. This feature ensures highly reliable communications. Unlike higher-level protocols such as TCP (Transmission Control Protocol) and STP (Spanning Tree Protocol) that set up alternate routes and retransmit lost Ethernet FRAMES, 802.1CB minimizes fluctuations in the latency time required for an Ethernet FRAMES to travel from source to destination when a failure occurs along the route.

For example, set two routes to your destination.

Duplicate the Ethernet FRAMES and send it along two paths.
If no failure occurs on Route 1 or Route 2 and two identical FRAMES arrive from each route, one FRAMES will be discarded and only the other FRAMES will be delivered to the destination. Note that the rule is that FRAMES that arrives last of the two FRAMES will be discarded.

If a failure occurs on route 2, FRAMES on route 1 is sent to the destination as is.

Before duplicating an Ethernet FRAMES and sending it over multiple routes, an R-Tag (Redundancy Tag) is added to each Ethernet FRAMES so that the receiving side can determine whether the same FRAMES has already been received.
The same FRAMES is sent over multiple routes with the same R-Tag sequence number.
The R-Tag is removed from FRAMES at the receiving end.

Summary

In this column, we explained 802.1CB (Frame Replication and Elimination for Reliability).
In the next column, we will explain 802.1Qci (Per-Stream Filtering and Policing).

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Introduction

What is 802.1CB?

The Need for 802.1CB

Summary

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