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15 Apr 2016
What Is 40 Gigabit Ethernet?

With the development of telecommunications, 40Gigabit Ethernet (40GbE) standard was launched by the IEEE in June 2010, which enables the transfer of Ethernet frames at speeds of up to 40 gigabits per second (Gbps). It also addresses physical layer specifications for communication across backplanes, copper cabling, multimode fiber and single-mode fiber. Nowadays, 40G applications are gaining more popularity with the development of the 40GbE. It become a new generation of high-speed, high-demand, computing applications and technologies.

Like 1GbE or 10GbE network, the heart of the 40GbE network layer is a pair of transceiver modules which are connected by a patch cable. The transceiver modules and patch cables seem to be the most basic components for transmission. The former is used to plug into either network servers or various components such as interface cards and switches.

40GbE Transceivers

40GbE transceivers are also developed along the way to meet the increasing demand for higher density and more bandwidths, from CXP, CFP to QSFP+ transceiver which will be introduced first below.

CFP transceiver is defined as hot-pluggable optical transceiver form factors to enable 40 Gbit/s and 100 Gbit/s applications, which is specified by a multi-source agreement to produce a common form-factor for the transmission of high-speed digital signals. The c stands for the Latin letter C used to express the number 100 (centum). CFP transceiver was designed after SFP transceiver interface, but it supports much larger internet speed — 100G, which is realized by using 10×10Gbit/s in each direction. Its larger size is suitable for the needs of single-mode optics and can easily serve multimode optics and copper as well.


CXP transceiver provides twelve lanes in each direction but is much smaller than the CFP and serves the needs of multimode optics and copper. The Roman number “X” means that each channel has a transmission rate of 10 Gbps. CXP is a kind of hot-pluggable transceiver with data rate up to 12×10 Gbps.

QSFP/QSFP+ transceiver with the similar size to CXP provides four transmit and four receive lanes to support 40GbE applications for multimode and single-mode fiber and copper today. It is the most popular interface of 40G transceivers now. Two main types of QSFP+ transceivers are used in the data center: short reach (QSFP-40G-SR4) for ~100 meters transmission on multimode fiber and long reach (QSFP-40G-LR4) for 100 meters to 10km using single-mode fiber. For insatnce, Juniper Networks JNP-QSFP-40G-LR4 compatible QSFP+ transceiver from FS.COM supports link length of 10km over single-mode fiber.


40GbE Cable Assemblies

The cabling for 40 GbE can be either fiber or copper. The supportable channel length depends on the cable and the transceiver type. With regard to connectors, the only significant change outlined in the 802.3ba standard is the use of MPO/MTP connectors at the multimode transceivers to support the multifiber parallel optics channels.

Cables used in 40 Gigabit Ethernet mainly include passive and active direct attach copper cables and active optical cable (AOC). The QSFP+ passive or active direct attach copper cables are designed with twinax copper cable and terminated with QSFP+ connectors. For instance, HP JG331A compatible QSFP+ to 4SFP+ passive copper cable is suitable for very short distances and offer a very cost-effective way to establish a 40-gigabit link between QSFP port and SFP+ port of HP switches within racks and across adjacent racks. The main difference between passive QSFP+ DAC and active QSFP+ DAC is that the passive one is without the active component. AOC is used for short-range multi-lane data communication and interconnect applications. It uses electrical-to-optical conversion on the cable ends to improve speed and performance of the cable without sacrificing compatibility with standard electrical interfaces.

Parallel Fiber Optic Transmission

Unlike the traditional Ethernet standard which has relied upon duplex fiber cabling with each channel using one fiber to transmit and the other to receive, 40GbE standard uses parallel optics for transmission. For 40GbE, a 12-fiber cabling solution with each channel featuring four dedicated transmit fibers and four dedicated receiver fibers is used. In general, the middle four fiber remain unused. Parallel transmission is also used for 100GbE with a 24-fiber solution or two 12-fiber solution.

Parallel Fiber Optic Transmission

The market for 40 GbE and 100 GbE will evolve over the next three to seven years as products become less expensive and more available over time. This post is a quick and simple overview of 40GbE and its fiber optic components of the interconnected foundation which may give you a general idea of 40GbE. If you have any demand for the 40GbE components or product solutions, please contact us via


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