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40G QSFP+ DAC and AOC, How to Choose

As one of the infrastructures that need to be considered when upgrading or building a data center, 40G DAC and 40G AOC are important to the data center. Deploying 40G DAC or AOC can effectively simplify wiring and reduce overall power consumption. However, how to choose the right product has become a difficult problem. This article will give you a deep understanding of DAC and AOC to help you make a choice.

What is 40G DAC

40G DAC is a highly economical solution for short-distance transmission, commonly used in data centers and high-performance computing applications. It consists of a twinaxial copper cable with QSFP+ connectors on both ends, which can be directly connected to devices such as switches or servers without connecting transceivers. There are several types of 40G: 40G QSFP+ to 40G QSFP+ DAC, 40G QSFP+ to 4x 10G SFP+DAC, their transmission distances range from 0.5 meters to 10 meters, and they can effectively connect devices through plug-and-play features, ensuring recommended deployment and simplifying network cabling. Unlike optical modules, 40G DAC does not have expensive optical devices and electronic components, and it consumes almost no power during transmission, which means it hardly generates heat. This makes 40G DAC an indispensable part of modern network infrastructure.

What is 40G AOC

40G AOC is composed of optical modules and optical fibers integrated. It has lasers and electronic components. Compared with 40G DAC, it provides a longer transmission distance and faster speed. It can seamlessly connect QSFP+ ports in switches and routers to ensure reliable data transmission through signal amplification over long distances. 40G AOC has two types: 40G QSFP+ to 40G QSFP+ AOC and 40G QSFP+ to 4x 10G SFP+ AOC. Standard AOC can meet the transmission distance of 1-30M.

40G DAC And AOC, How to Choose

So how do you choose to use DAC or AOC on the Internet? Next, I will take you to explore in depth several aspects to help you make a decision:


When you build a network, if the cost is an important consideration for you, then 40G DAC is undoubtedly your best choice. DAC uses copper cables and QSFP+ connectors, without expensive lasers and electronic components, so its cost is lower, and it is suitable for short-distance and budget-limited network architectures. AOC combines optical modules and optical fibers. It has lasers and electronic components, which can provide longer distance transmission and more reliable signal transmission, but its cost is relatively much higher than DAC. Therefore, if your budget is insufficient, then choosing DAC is undoubtedly a good choice. AOC is suitable for longer distances and more stable signal transmission.

Operational costs

In daily operations, since DAC is composed of copper cables and has no lasers or electronic components, its power consumption is very low, about 440mW in 40G transmission, while AOC consumes 2W. In data centers, the most expensive part is the cooling system. The higher the power consumption, the higher the heat. From the perspective of operating costs, DAC with lower power consumption is undoubtedly the right choice. It not only has low power consumption, but also lower deployment costs.

Transmission stability

In terms of transmission stability, AOC is undoubtedly better than DAC. Due to the existence of electromagnetic interference, DAC uses copper cables for signal transmission, and the electrical signals inside are easily affected by electromagnetic interference, thus affecting the data transmission quality. AOC uses optical fiber for data transmission, and the optical signal is transmitted inside, which is not affected by electromagnetic interference. So when you choose to deploy in an environment with strong electromagnetic interference, AOC is undoubtedly a better choice.

Transmission distance

The transmission distance of DAC is generally within 5M, while that of active DAC can reach 10M. This transmission distance is generally suitable for connections within a rack or between adjacent racks. Since AOC uses optical signals for transmission, its maximum transmission distance can reach 100M. If your transmission distance is within 10M, you can choose DAC. If the transmission distance is above 10M and within 100M, then AOC is a better choice.


In general, 40G DAC and AOC are important parts of modern network infrastructure. 40G DAC is suitable for environments with low budget, short-distance transmission, and focus on operating costs. 40G AOC provides longer distance and more stable signal transmission, but its deployment and operating costs are relatively high. You can consider your network environment comprehensively and choose the product that suits you.

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