100GBASE-SR4 is one of the latest physical layer (PHY) standards under development in the IEEE 802.3bm task group.

While IEEE 802.3 already includes specifications for 40 Gb/s and 100 Gb/s over multimode fiber, this new 100 Gb/s standard is intended to provide a more cost effective option with reduced power and increased density.


What Are the Characteristics?

Compared to the existing 20-fiber link used by the current 100GBASE-SR10 standard (10 transmit, 10 receive), 100GBASE-SR4 aims to use an 8-fiber link with four 25 Gb/s lanes in each direction.

The media dependent interfaces in the IEEE 802.3 Standard are defined in separate clauses as follows: Clause 84 for 40GBASE-KR4, Clause 85 for 40GBASE-CR4, Clause 86 for 40GBASE-SR4, Clause 87 for 40GBASE-LR4/ER4, Clause 88 for 100GBASE-LR4/ER4, and Clause 92 for 100GBASE-CR4.

The 100GBASE-SR4 100 Gb/s PHY will be defined in Clause 95 of the IEEE 802.3 Standard. All these interfaces use a 4-lane data path.


There are various flavors of 40 gigabit and 100 gigabit Ethernet (GbE) applications, each with their own salient characteristics as summarized in the table.

What’s The Outlook?

While much progress has been made, the timeline for the completion of 100GBASE-SR4 is still about a year away.

The new 100GBASE-SR4 will likely use a smaller interface than the CXP form factor used for 100GBASE-CR10/SR10. I recently saw an announcement from Avago Technologies where they have demonstrated their new generation 100G QSFP28 SR4 optical transceiver module solutions using live traffic streams of 100 GbE data transmitting over a 100 meter OM4 optical fiber cable. This module uses the QSFP28 form factor, which is the same physical size as 40GBASE-SR4.

This is indeed exciting. We are seeing the next generation migration path from 40 Gb/s to 100 Gb/s coming to fruition in the very near future—all of which will be supported over OM4 multimode fiber with 12-fiber MPO connectivity.

With our FiberExpress product family complete with low loss 12-fiber MPO connectivity and OM4 fiber solutions, Belden is well positioned to help you smoothly transition from 10 Gb/s to 40 Gb/s to 100 Gb/s.

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