In today's digital age, data centers serve as the backbone of countless industries, ensuring the seamless flow of information and maintaining the integrity of critical data. To keep these data centers running efficiently, choosing the right cabling solution is paramount. Two popular options in this regard are Direct Attach Copper (DAC) cables and Active Optical Cables (AOC). In this article, we will explore the intricacies of these cabling solutions, compare their pros and cons, and help you make an informed decision.
A Direct Attach Cable (DAC) consists of a twinax copper cable with connectors like SFP+, SFP28, QSFP+, QSFP56, or QSFP28 on both ends, allowing for a direct electrical connection to active equipment. DAC cables can be divided into two categories: passive DAC and active DAC. Both passive and active DAC cables enable the transmission of electrical signals directly over copper cables. Passive DACs do this without any signal conditioning, while active DACs have built-in electrical components within the transceivers to amplify the signals. Typically, DAC cables are used for connecting switches, servers, and storage devices within racks.
An Active Optical Cable (AOC) is composed of a multimode fiber optic cable with SFP+, SFP28, QSFP+, QSFP56, or QSFP28 optical transceivers at both ends. It relies on external power to facilitate the conversion of signals, transitioning from electrical to optical, and then back to electrical. In broad terms, AOC cables are primarily employed for connecting switches, servers, and storage devices located in separate racks within data centers.
DAC cables are utilized for establishing connections among switches, servers, and storage units within the same rack. In contrast, AOC cables are primarily employed to interconnect switches, servers, and storage devices situated in distinct racks within data centers. Additionally, DAC and AOC cables exhibit differences in the following aspects.
| DAC | AOC | ||
| 功耗 | Power Consumption | ＜1W | 1-3W |
| 传输距离 | Transmission Distance | ＜7M | ＜300M |
| 传输介质 | Transmission medium | Copper Cable | Fiber Optics |
| 传输信号 | Transmission signal | Electric Signal | Optical Signal |
| 价格 | price | Lower | Higher(Contains laser at both ends) |
| 重量体积 | Weight Volume of the same length | Bigger | Smaller |
Power Consumption
AOC cables require 1-2 watts, and they typically consume more power compared to DAC cables. Active DAC cables use less than 1 watt of power, while passive DAC cables are extremely power-efficient, using less than 0.15 watts, thanks to the thermal design of direct attach copper cables. Consequently, by opting for DAC solutions, operating costs related to power consumption can be reduced.
By adopting optical fiber technology, AOC cables are capable of transmitting signals over longer distances, reaching up to 100 meters. In contrast, DAC cables have limitations on their link length, with passive DAC cables reaching around 7 meters and active DAC cables extending up to 10 meters. In summary, DAC cabling solutions are well-suited for short-range transmissions, while AOC solutions are employed in scenarios requiring longer-distance networking.
It's important to note that the maximum distance over which a signal can be transmitted via a DAC cable can vary depending on the data rate. As the data rate increases, the link length decreases. For instance, 100G DAC cables may only support transmission up to 5 meters.
In broad terms, DAC cables have a simpler internal design with fewer components, and copper cables are considerably less expensive than fiber cables. When deployed in extensive data centers, choosing DAC cables in large quantities can lead to significant cost savings compared to AOC alternatives. DAC offers a cost-effective solution for short-range uses. However, for longer-range applications, it is prudent to consider the overall costs by making a detailed comparison between these two options.
Electromagnetic interference (EMI) pertains to disruptions caused by external sources that can impact an electrical circuit. As previously explained, active optical cables incorporate optical fibers, which are dielectric and do not conduct electric current. Consequently, AOC cables are resistant to electromagnetic interference and can be utilized in a wide range of scenarios. On the other hand, direct attach copper cables, due to their use of copper for transmitting electrical signals, are susceptible to EMI. Therefore, the environment in which these cables are used is crucial to prevent unwanted disruptions, performance degradation, or even total system failure.
DAC cables offer high bandwidth and performance for short-range connections, making them cost-effective solutions. In contrast, AOC cables utilize optical fibers and provide even higher bandwidth, ideal for longer distances, while remaining resistant to electromagnetic interference, ensuring reliable performance in diverse applications.
DAC cables are rigid and have limited flexibility due to their copper construction, making them suitable for fixed installations with short to moderate lengths. AOC cables, with their lightweight optical fibers, offer greater flexibility and can cover longer distances, making them versatile for various networking scenarios.
Influenced by the factors mentioned above, DAC and AOC cables are typically employed in different working environments.
DAC Cable Typical Application:
10G SFP+ DACs are primarily used for connecting switches and servers either within the same rack or in proximity to it. In essence, these 10G direct attach cables serve as an alternative for interconnecting Top of Rack (ToR) switches with servers or for stacking 10GbE switches. Given that 10G SFP+ DAC cables typically support link lengths of up to 7 meters while offering low power consumption, minimal latency, and cost-effectiveness, they prove to be an excellent choice for short-range server-to-switch connections.
10G SFP+ AOC Cable Typical Application
10G SFP+ AOCs find widespread application in various data center locations, including Top of Rack (ToR), End of Row (EoR), and Middle of Row (MoR). Similar to DACs, servers connect to Top of Rack Ethernet switches, with each server having one or two Ethernet connections that can be interconnected using AOC cables. Furthermore, 10G AOCs are employed in critical networking areas like Spine, Leaf, or Core switches, enabling interconnections with a theoretical maximum reach of up to 100 meters.
Are AOC cables more reliable for long-distance connections?
Yes, AOC (Active Optical Cable) cables are generally more reliable for long-distance connections compared to traditional copper cables like DAC (Direct Attach Cable). AOC cables use optical fibers, which offer greater signal integrity and resistance to electromagnetic interference, making them a reliable choice for extended distance data transmission.
Can I mix DAC and AOC cables in my data center?
Yes, you can mix DAC (Direct Attach Cable) and AOC (Active Optical Cable) cables in your data center, as long as they are compatible with the devices and applications you are using. It's essential to ensure that the connectors and specifications match your equipment and the desired data transmission requirements. Mixing cable types can provide flexibility in connecting different components within your data center.
Do DAC cables require special installation skills?
No, DAC (Direct Attach Cable) cables typically do not require special installation skills. They are designed for ease of use and often feature connectors that can be plugged in without extensive technical knowledge. However, it's important to follow the manufacturer's guidelines and ensure proper alignment during installation to avoid damage or connectivity issues.
How can I ensure the scalability of my data center cabling infrastructure?
Ensure data center cabling scalability by planning for future growth, using structured cabling, modular components, proper labeling, high-quality cables, and efficient cable management. Address power and cooling needs, conduct regular maintenance, and stay updated on evolving technologies for a future-proof infrastructure.
