How to Choose between 40G DAC and 40G AOC?

When upgrading or building a data center network infrastructure, one of the critical decisions to make is choosing between 40G Direct Attach Copper (DAC) cables and Active Optical Cables (AOC). Both options offer high-speed connectivity for data transmission, but they differ in their construction, performance, and suitability for various network scenarios. Understanding the differences and assessing your specific requirements is crucial for making an informed decision. This article will delve into the key factors to consider when choosing between 40G DAC cables and AOCs , helping you navigate through the selection process with confidence and clarity.

What Is the 40G AOC?

A 40G AOC integrates fiber-optic transceivers and optical fibers, surpassing copper cables in 40G networks. Leveraging optical technology, it offers faster speeds and longer reach. With QSFP+ connectors, it seamlessly interfaces with 40G QSFP+ ports in data center switches and routers, ensuring reliable data transmission with signal amplification over extended distances. Available variants include 40G QSFP+ AOC, 40G QSFP+ to 4x SFP+ breakout AOC, and 40G QSFP+ to 4x duplex LC breakout options. Renowned for adaptability, easy installation, and exceptional performance, 40G AOCs are favored in data centers, catering to various network needs like high-performance computing, cloud services, and data storage, vital for modern network infrastructures.

What Is the 40G DAC?

40G DAC cables offer a cost-effective, high-speed solution for 40G network data transmission. It comprises twin axial copper cables with QSFP+ connectors on each end, directly linking switches, routers, or servers without transceivers. QSFP+ DAC cables come in three variants: QSFP+ to SFP+ DAC, 40G QSFP+ to QSFP+ DAC, and QSFP+ to 4x SFP+ breakout DAC, providing low latency and power consumption, ideal for short-range data center connectivity. Available in lengths from 1 to 10 meters, they efficiently connect nearby devices with plug-and-play simplicity, ensuring easy installation and streamlined network deployments. Unlike optical modules, DAC cables lack costly optical lasers and electronic components, resulting in significant cost and power savings for short-distance applications. Widely used in data centers, they support high-performance computing, cloud services, and storage applications, offering affordability, reliability, and compatibility with standard QSFP+ ports, making them integral components in modern network infrastructures.

40G DAC vs. AOC: Choosing the Right Option

In high-speed networking, selecting between 40G DAC cables and AOCs is crucial, impacted by key factors including cost, transmission distance, power consumption, and cooling system needs. Comprehensive comprehension of these aspects is vital for informed decision-making:

Cost Issues

Cost significantly influences your choice. DAC cables, with their simpler copper conductor construction, usually have a lower initial cost compared to AOCs, making them preferable for short-distance connections with budget constraints. Conversely, AOC cables, leveraging optical fibers and advanced tech, come with a higher upfront investment despite offering superior signal integrity and longer transmission distances. Passive DAC cables are cheaper than AOC. DAC cables provide a cost-effective solution for short distances, while AOCs are more suitable for longer distances and enhanced signal integrity.

Transmission Distance

When data rates are below 5 Gbps, passive DAC cables are commonly used for interconnection, providing cost-effective and reliable connectivity without requiring power. However, for 40Gbps transmission, passive DAC cables have limited capability, supporting only short distances due to their design. To address this limitation, AOCs are introduced, offering thinner, more flexible cables capable of reaching distances up to 100 meters. Despite being more expensive, AOCs provide extended reach compared to passive DAC cables. Active DAC cables, while not matching AOCs' transmission distances, still surpass passive DAC cables, with a 40G transmission distance of about 10 meters. In summary, for longer transmission distances, AOCs are preferred, followed by active DAC cables, while passive DAC cables are suitable only for very short 40G transmissions.

Power Consumption

When choosing between 40G DAC cables and AOCs, understanding power consumption is vital. DAC cables draw approximately 440mW for 40G transmission, much lower than AOCs' 2W consumption. This lower power requirement enhances energy efficiency and reduces heat generation in data centers, optimizing reliability. AOCs typically require 1 to 2 watts due to their active components. DAC cables, on the other hand, offer a more energy-efficient solution. Higher power consumption can increase heat generation, affecting cooling needs. Therefore, prioritizing power efficiency and cooling considerations may lead to preferring DAC cables. However, it's crucial to consider factors like signal integrity and transmission distance for a well-informed decision.

Cooling System

Cooling is vital for data centers, impacting their reliability and lifespan. When selecting DAC cables, two key factors influence data center cooling: cable size and power consumption. Thinner cables enhance dispersion within the data center. AOC cables are thinner than DAC cables, and active DAC cables are thinner than passive DAC ones. Higher power consumption leads to increased heat generation, straining the cooling system. AOCs require the highest power, while passive DAC cables require the lowest.

Conclusion

After assessing DAC and AOC performance, it's evident that passive DAC cables are suitable for short-reach applications, while AOCs offer superior transmission but at a higher cost and power consumption. Active DAC cables support 40G transmission up to 10 meters with low power usage, meeting standard interconnection needs for distance and cooling in most data centers. Additionally, DAC cables are more cost-effective.