An Introduction to FlexEthernet (FlexE)

An Introduction to FlexEthernet (FlexE)

As maximizing bandwidth remains the paramount concern for network operators, backward compatibility and forward flexibility become increasingly important. Extending the life of currently-deployed equipment can defray some of the cost of network upgrades, while the networks of the future will require operators to exert a greater level of control to adapt immediately to changes in traffic. To this end, the Optical Interoperability Forum (OIF) has put forth a standard for Flexible Ethernet (aka FlexEthernet or FlexE), an evolutionary next step beyond traditional Ethernet designed to support network needs of the future.

What Is FlexE?

FlexE is a communications protocol that improves the flexibility of networks beyond traditional Ethernet. It allows network operators to optimize the flow of traffic across their networks by combining and separating across different IEEE Ethernet standards. Specifically, its key performance features include: bonding, sub-rating, and channelization.


The bonding of multiple links combines multiple links into a single higher-speed link (for example, four 100G links into a 400G data pipe), as shown below:

Via Optical Interoperability Forum.

This can be tremendously useful for efficiently providing higher capacity for data center interconnect (DCI) applications. While conceptually similar to traditional Layer 2 link aggregation (LAG), FlexE bonding occurs at the physical layer.  Additionally, it can utilize the entire bandwidth of the aggregated link, instead of the 70-80% maximum with LAG.

Sub-Rating and Channelization

On the other hand, certain applications will require using only part of a higher-bandwidth link. Maybe the ideal bandwidth of a purchased link is lower than that of the physical interface. Maybe you need to reduce Ethernet rates to match lower-rated links. This is where sub-rating comes into play, as an alternative to flow control. A sub-rating use case is shown in the diagram below:

Via OIF.

Channelization enables network operators to more efficiently map multiple services of different Ethernet ratings onto a common interface. In this way, it bridges some of the functionality between Optical Transport Network (OTN) and Ethernet protocols. An example of multiple channelized links is shown below:

Via OIF.

Another important attribute of FlexE is its backward compatibility. It can interface with existing transport infrastructure that is not aware of FlexE. It makes use of standards-based optical modules, cables, and backplanes.

As network operators explore software-defined networking (SDN) solutions to evolve their networks, Flex Ethernet can be a valuable tool for exercising more dynamic control without a full transport infrastructure overhaul. To discuss open networking and SDN solutions further, contact us today.

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