Why Not Use QSFP DAC Twinax Cable for 40G Cabling?

With the growing network requirements for higher network speed, greater scalability, higher performance and reliability, 40G network gradually becomes a better choice for most data centers. Under this condition, the 40G QSFP+ copper direct attach cable(DAC) came into market, which is designed for delivering an aggregate data bandwidth of 40Gb/s in a short distance and high density cabling interconnect system. As a highly cost-effective solution for 40G to 40G or 10G to 40G connection, there is no doubt that the QSFP DAC twinax cableplays an important role in 40G cabling for better meeting the increasing requirements.

QSFP DAC twinax cable is also referred to as QSFP+ copper direct attach cable or QSFP copper cable, used for connecting switch to switch or switch to sever. It can be simply divided into three types, QSFP+ to QSFP+ direct attach copper cable, QSFP+ to 4 SFP+ direct attach breakout copper cable and QSFP+ to 4 XFP breakout copper cable. Since the first two types of QSFP DAC twinax cables are more commonly used, the following will mainly talk about these two kinds of QSFP DAC twinax cables.

As for the QSFP+ to QSFP+ direct attach copper cable, it generally consists of a length of copper twinax cableand two QSFP+ connectors, used for 40G to 40G connection, which is capable of distances of up to 10 meters. As for the QSFP+ to 4 SFP+ direct attach breakout copper cable, it is designed for 10G to 40G short reach applications up to 5 meters. Compared to the previous copper cable, it is more complicated, fitted with one QSFP+ connector on one end of the copper twinax cable and four SFP+ connectors on the opposite end of the copper twinax cable.

We used to choose fiber optic transceiver and patch cable to deploy the fiber link, which requires us to firstly insert the transceiver to the switch and then connect the patch cable to the transceiver. However, for the QSFP DAC twinax cable, it can be directly plugged into the switch to finish the 40G connection, without any transceiver, as shown in the following figure. In short, the QSFP DAC twinax cable is really a cost-effective solution for interconnecting high speed 40G switches to 40G switches or 40G switches to existing 10G equipment.

If you want to deploy a 40G to 40G connection, then you are suggested to choose the QSFP+ to QSFP+ direct attach copper cable that provides a highly economical way to set up a 40G short distance link between QSFP+ ports of QSFP+ switches within racks and across adjacent racks. In principle, this kind of QSFP DAC twinax cable enables four-lane high speed interconnects, and each of the lane operates at 10Gb/s transmission speeds like the lane of SFP+ cable. Obviously, one QSFP+ to QSFP+ direct attach copper cable link is equivalent to 4 SFP+ cable links, that provides greater density and reduced system cost.

As we know, most data centers can deployed switches with 40G Ethernet ports, but their servers are still fitted with 10G Ethernet ports. Taking this case into consideration, the QSFP+ to 4 SFP+ direct attach breakout copper cable should be chosen for the 10G to 40G connection. When putting it into use, the QSFP+ connector will be connected to the 40G QSFP port of a switch on one end, while the four SFP+ connectors will be connected to four 10G SFP+ ports of a switch on the other end. Thatrsquo;s to say, it allows a 40G Ethernet port to be used as four independent 10G ports thus providing increased density, while permitting backward compatibility and a phased upgrade of equipment.

QSFP DAC twinax cable is an ideal solution for 40G to 40G or 10G to 40G connection, which is highly cost effective to meet the increasing requirements of 40G network. At present, there are two main types of QSFP DAC twinax cables. One is the QSFP+ to QSFP+ direct attach copper cable, which is very suitable for 40G to 40G connection with the distance up to 10 meters. And the other is the QSFP+ to 4 SFP+ direct attach breakout copper cable that can be used for 10G to 40G short reach applications up to 5 meters.