Design Elements of 40G Ethernet Era

Design Elements of 40G Ethernet Era

In the past 10 years, the Ethernet rate has experienced the transition from 100M network to Gigabit and 10G network. With the expected peak of 10 Gigabit networks around 2015, it is particularly urgent to avoid network bottlenecks. 

At present, servers with 10G uplink ports have been widely used in data centers, and servers with 40G uplink ports are also eager to try. In order to cope with the excessive occupation of aggregation link and backhaul link resources caused by the rapid growth of server rate, IEEE 802.3ba HSSG has started to define MAC parameters, physical layer specifications, and management parameters, and has successfully realized that the next generation Ethernet can transmit 802.3 format frames at 40G and 100G rates. Just as IEEE evolved to improve Ethernet to a higher rate in the past, smoothing is the most important consideration. However, the evolution to 40G/100G is still very different from the past. This paper will focus on these differences and pay attention to many elements that can change and affect the design concept of the data center.

New Interface of Optical Transceiver: MPO Connector

For Ethernet, the continuous emergence of new technologies and the wide application of high-speed data networks are not new, but this evolution to 40G/100G is fundamentally different from the previous rate improvement. An important difference is that the difficulty of VCSEL signal modulation increases, which promotes the birth of multi-core fiber parallel optical transmission technology.

In the single 10G Optical fiber transmission, it is used for 4 “receiving and transmitting” optical fibers. Similarly, in 100G technology, the single-core fiber of “10 receiving and 10 transmitting” is used. Another problem caused by the difference is how to specify these two new transmission rates, which is quite different from the previous 10 times rate progression. Although some users strongly request to bypass 40G technology and directly evolve to 100G, HSSG has formulated 40G and 100G rate standards for the consideration of different rate requirements of the current growing network applications in the data center, especially for the applications of network computing and core networking.

HSSG believes that 40G transmission rate is an ideal choice for servers, high-performance computing clusters, blade servers, storage area networks and network storage, while 100G technology is conducive to the switching, routing and aggregation services of data centers.

Another big change is the adoption of fiber optic connector technology that supports higher rates. With the improvement of network speed, all other forms of optical fiber connectors have been greatly eliminated except dual-core SC and LC. 40G/100G Ethernet provides higher speed. Therefore, MPO optical fiber connector technology is introduced to equip large-scale optical fiber ports of active equipment and quickly integrate them into various fields of data centers.

MPO Connector

Over the past decade, as an emerging technology, MPO’s industry-recognized value-added modular scheme has been widely used in the physical layer deployment of data centers, but it has not been scaled up on the optical transceiver port. TIA-604-5-C optical fiber connector interactivity standard defines MPO. MPO type connector is an array connector that can realize up to 72 core optical fibers on the plug-in end face of a single connector.

In fact, the MPO connector can support a variety of requirements in terms of the number of fiber cores, and the 12 core MPO is only a general version of the current application. The type of optical fiber transceiver port realizes the transformation from the currently dominant dual-core LC to MPO technology. The supplier needs to solve the upgrading of corresponding component products in the physical layer, which also depends on how the network designer plans to build a 40G/100G data center.

40G Standard Terms

As mentioned earlier, HSSG has developed a 40G standard to support high-performance computing clusters, blade servers, storage area networks, and networked storage. 40G commercial servers will be realized in the next 2 to 3 years. The optical fiber transceiver of the 40G network will become the QSFP optical module with 12 core MPO. Using MPO technology, the deployment of multimode optical fiber in the 40G network is realized by using “4 transmitting and 4 receiving” in 12 core optical fibers. Each of the four “channels” is used to transmit a 10G rate and 40G. The transmission of single-mode fiber is still realized by CWDM Technology of the dual-core connector.

The 40G network transmission media defined by HSSG include:

(1) 40GBase-SR4: 100m OM3; 125m OM4-10Gx4 core, each direction.

(2) 40GBase-LR4: Sparse wavelength division multiplexing – 10km single-mode – 4x10G works at 1300nm wavelength.

(3) 40GBase-CR4: 7m/copper 4x10G.

QSFPTEK 40G QSFP+ SR4 and LR4 Transceivers

Note that the first method above defines two multimode fibers:

(1) The transmission distance of 2000MHz · km OM3 multimode fiber can reach 100m.

(2) The transmission distance of 4700mhz · km OM4 multimode fiber can reach 125m.

40G Evolution Path

For the installed 12 core MPO optical fiber module system to evolve to 40G, simply remove the existing module from the equipment cabinet and cross-connected optical fiber distribution frame and replace it with MPO optical fiber adapter panel. Secondly, the cross-connection in the trunk distribution area and the interconnection of QSFP are completed by using the appropriate 12 core MPO optical fiber jumper. Although the 24 core MPO connector has not achieved commercial scale in the pre-connection system at present, this 24 core MPO connector will be adopted in the future, whether in the trunk optical cable or optical fiber module. Based on this, the 40G network inevitably requires the deployment of branch jumpers for the connection between QSFP and trunk optical cables, and pre terminate two 12 core MPO connectors and one 24 core MPO connector at both ends. In this way, the necessary interfaces are provided for the QSFP based on 24 core MPO backbone optical cables and 40G. At the same time, a 24 core MPO optical fiber jumper for system cross-connection provides the necessary guarantee for polarity maintenance and meeting jitter requirements.


More and more physical layer suppliers are actively preparing, planning, and promoting their 40G/100G solutions. QSFPTEK can provide one-stop 40G and 100G optical products to ensure the compatibility, scalability, and effectiveness of network infrastructure, and help your data center prepare for the upcoming 40G/100G channel.