40G QSFP Cable Basics and 40G copper cable types
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40G QSFP+ Direct Attach Copper Cabling

Posted on by FS.COM

Today’s enterprise data centers and networking environments are undergoing an infrastructure transformation, requiring higher speeds, greater scalability, and higher levels of performance and reliability to better meet the demands of business. As speed and performance needs increase, migration to 40G is imperative. QSFP+ direct attach copper cable is the cost-effective way to upgrade from 10G to 40G or 40G to 40G interconnect connection.

40G QSFP+ Direct Attach Copper Cable (DAC) Basics

40G QSFP+ direct attach copper cable, or 40G QSFP+ DAC is a high speed twinax cable with QSFP+ connector on either end of the cable. It is designed to meet emerging data center and high performance computing application needs for a short distance and high density cabling interconnect system capable of delivering an aggregate data bandwidth of 40Gb/s. The maximum transmission distance of QSFP+ direct attach copper cable is 10 meters, which makes the cable suitable for in-rack connections between servers and Top-of-Rack (ToR) switches because they often require shorter distances and not routed to the Main Distribution Frames.

qsfp cable

Types of 40G QSFP+ Direct Attach Copper Cable (DAC)

According to the connector types on both ends, QSFP+ direct attach copper cables can be mainly divided into two types. One is QSFP+ to QSFP+ direct attach copper cable, and the other is QSFP+ to 4 SFP+ direct attach breakout copper cable. In addition, there is a third type QSFP+ direct attach copper cable called QSFP+ to 4 XFP direct attach breakout copper cable which is not as common as the former two types. And by the internal housing structure, 40G QSFP+ direct attach copper cables can be classified into QSFP+ passive DAC and QSFP+ active DAC. QSFP+ active copper cable contains electronics for signal conditioning, while QSFP+ passive copper cable does not contain electronics for signal conditioning. Thus QSFP+ passive DACs do not need power for internal electronics and do not consume any power or produce any heat, whereas QSFP+ active DACs require some power to make the internal circuits work and are able to bridge longer distances.

How to Use 40G QSFP+ Direct Attach Copper Cable (DAC)?

Before building the network, it is necessary to buy 40G DAC cables from reliable QSFP cables supplier and manufacturer. Only in this way can the whole link work at high level. This part will focus on the applications of 40G DAC cable.

40G QSFP+ to QSFP+ DAC Used in 40G to 40G Connection

In 40G to 40G connection, QSFP+ to QSFP+ direct attach copper cables are suitable for very short distances and offer a highly cost-effective way to establish a 40G link between QSFP+ ports of QSFP+ switches within racks and across adjacent racks. These QSFP+ copper cables connect to a 40G QSFP port of a switch on one end and to another 40G QSFP port of a switch on the other end. It is noted that the distance between the two switches is within the cable length. The cabling diagram is shown in the following figure.

40G QSFP+ Direct Attach Copper Cable in 40G to 40G Connection

40G QSFP+ to 4xSFP+ DAC Used for 10G to 40G Migration

For 10G to 40G migration, we can use a 40gbe breakout cable—QSFP+ to 4xSFP+ direct attach breakout copper cable. The 40G QSFP+ connector on one end is inserted into a 40G QSFP+ port of a switch and the four 10G SFP+ connectors on the other end are inserted into 10G SFP+ port of four switches. This allows reliable migration from 10G to 40G in short reach. The cabling diagram is shown in the following figure.

40G QSFP+ to 4xSFP+ DAC Used for 10G to 40G Migration

Why Use 40G QSFP+ Direct Attach Copper Cable (DAC)?

For 40G short reach applications, 40G QSFP+ direct attach copper cable provides simple and inexpensive cabling solution. The main advantages are listed below.

 Robust: Different from a transceiver module, DAC cables do not have any connectorization on the back or may need patch panels and patch cords. And this makes DAC cables sturdier and more reliable and less space hungry.
 Cheap: It is undeniable that copper cabling is the least expensive way to interconnect high speed systems together. Therefore, 40G QSFP+ direct attach copper cabling is the cheapest solution for 40G short links.
 Low-power Consumption: Denser equipment will consume more electrical power, which will also produce more heat. While DAC cables have the potential to reduce the overall power consumption and heat dissipation.
 Easy Operation: When deploying the network, the whole link is easily accomplished by inserting the connectors on both ends of DAC cables into the corresponding ports on the switches.

40G DAC vs. 40G AOC vs. 40G Transceiver

On the market, there are three options for 40G cabling, 40G DAC, 40G AOC and 40G transceiver. How to make choice among them?

Transmission Distance Under 5m

When the transmission distance is under 5m, using reliable QSFP+ passive copper cable is recommended. Though AOC cable is also designed for short link, from the perspective of cost, reliable QSFP+ direct attach passive copper cable could save about 60% or more.

Transmission Distance Between 5m and 100m

When 40G link distance is between 5m and 100m, 40G QSFP+ AOC is more suitable as its maximum transmission is longer than DAC cable’s. In addition, AOC cable is thin and has better bend radius than DAC, which can save space for data center.

Transmission Distance Above 100m

If the link distance is longer than 100m, you can choose 40G QSFP+ SR4 transceiver, working with OM3 over 100m or OM4 over 150m. But if the 40G network is deployed over long distance, 40G QSFP+ LR4 transceiver and singlemode fiber will be the choice.

Conclusion

In today’s network building, high-speed and cost-effective cabling solution is preferable. Characterized by low price and simple operation, 40G DAC cable gains great popularity among data center users. It not only can achieve 40G to 40G reliable connection, but also can provide smooth migration from 10G to 40G. Since many vendors can offer this high-speed cables, when start your networking, you’d better buy 40G QSFP+ direct attach copper cable from reliable supplier and manufacturer. That’s the necessary condition for high network performance.

Related Article: 40G Data Center Cabling Solutions Comparison

 

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