Notes on 40 Gigabit Ethernet Standard

The increasing deployment of standard Ethernet has driven data centers to migrate from traditional tree topologies to spine and leaf layouts. Fiber networking infrastructure has evolved quickly from 10G rack-to-rack connectivity to the 40G or even 100G which has been accepted by carrier network. With bandwidth in the data center now increasing from 10 Gbps to 40 Gbps, there are several aspects to consider when establishing 40Gigabit Ethernet (GBE) links, such as the cable requirements for 40 Gbps.

40G Cable Requirements

There are generally 4 cabling options for 40 Gigabit Ethernet. The first one is direct attach copper (DAC) cables for distances below 10m, the second one is laser optimized OM3 or OM4 fiber cables for up to 100m and 150m respectively, the third one is active optical cables (AOC) for adjacent rack to rack distances – typically below 15m (although 150m is possible), the last one is QSFP+ to 4 SFP+ breakout cables (eg. QSFP-4SFP10G-CU1M). Here detailed information goes to the first cabling option.

40G QSFP+ DACs include 40G QSFP+ direct attach active copper cables and 40G QSFP+ direct attach passive copper cables, with the latter type widely used for 40G network connectivity. For example, QFX-QSFP-DAC-1M is the QSFP+ to QSFP+ direct attach passive copper cable assembly. This Juniper QFX-QSFP-DAC-1M product listed on Fiberstore is a very cost-effective way to establish a 40-gigabit link when the required length is 1m. The image below is QFX-QSFP-DAC-1M product.


40G Optical Transceivers Types

40G optical transceiver types include QSFP+ transceivers and CFP transceivers. The main focus of this article is the 40G QSFP. The transceiver is an electronic device that receives an electrical signal, converts it into a light signal, and launches the signal into a fiber. It also receives the light signal, from another transceiver, and converts it into an electrical signal.

40G QSFP is the dominant transceiver form factor used for 40 Gigabit Ethernet applications. In 2010, the IEEE standard 802.3ba released several 40-Gbps based solutions, including a 40GBASE-SR4 parallel optics solution for multi-mode fiber (MMF), and 40GBASE-LR4 optical transceivers for serial transmission at 4 wavelengths over single-mode fiber (SMF).

  • 40GBASE-SR4 Transceiver

This 40GBASE-SR4 (“short range”) QSFP+ transceiver transmits signal over 8 fibers (4 pairs) within the single connection port, with each pair offering a 10G channel. To connect to this 40G QSFP, a 12 fiber MPO style connector is used with only 8 of the 12 fibers deployed.

  • 40GBASE-LR4 Transceiver

40GBASE-LR4 (“long range”) is a port type for SMF and uses 1300nm lasers. It uses four wavelengths delivering serialized data at a rate of 10.3125 Gbit/s per wavelength. Like MC2210511-LR4, Fiberstore compatible MC2210511-LR4 realizes 40G links over SMF with the maximum link length is 10km.


Quick Notes on 40GbE Standard

After introducing some basic information on 40GbE standard, a simple note on it is necessary. IEEE 802.3ba standard for 40G Ethernet. 40G Ethernet over OM3 or OM4 requires parallel optics 40GBASE-SR4, while 40G Ethernet over SMF uses serial transmission at 4 wavelengths 40GBASE-LR4. The maximum distance for OM3 is 100m with the maximum allowable insertion loss less than 1.9dB. The maximum link length for OM4 is 150m with the maximum insertion loss below 1.5dB.


40GbE infrastructure offers solutions to address the current bandwidth requirements as well as future bandwidth growth. When establishing 40G links, it’s important to create a carefully planned cabling system to performed tasks. Fiberstore supplies various numbers of 40G QSFP+ transceivers and cables which offer customers a wide variety of high-density and low-power 40G connectivity options. For more information about 40G solutions, you can visit Fiberstore.

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