DAC, AEC, AOC, and ACC High-Speed Data Transmission Cable Guide

DAC, AEC, AOC, and ACC High-Speed Data Transmission Cable Guide

• 2025-01-10 11:38:28
• by Admin

In today's highly competitive communication industry, everyone hopes to gain a competitive edge, whether in terms of performance, efficiency, or cost. Although many data center renovations focus on network adapter and switch configurations, an extremely fundamental yet equally effective way to improve the deployed data centers is to rethink the interconnecting cables. Currently, there are four different forms of data transmission cables on the market, namely DAC (Direct Attach Cable), AOC (Active Optical Cable), AEC (Active Electrical Cable), and ACC (Active Copper Cable), which differ in transmission media, performance characteristics, and application scenarios. Let's get to know DAC, AEC, AOC, and ACC together today. Which one will be the ultimate winner in the field of data communication?

DAC High-Speed Cables

Technical Principle:

DAC high-speed cables (Direct Attach Cable), generally translated as direct cables or direct copper cables, are usually cable assemblies purchased in fixed lengths with fixed connectors at both ends. The ports cannot be replaced, and the module heads and copper cables cannot be separated. High-speed cables have been increasingly accepted and used by more and more users due to their remarkable advantages such as high-cost performance, high efficiency, high speed, high integration, and low loss. They have become the first choice for high-speed data communication solutions and are widely used in storage area networks, data centers, and high-performance computer connections.

Basic Structure of High-Speed Cables:

They mainly consist of core wires with silver-plated conductors and three insulating materials including foamed insulation, Teflon, and PP. Then, wire pair shielding and overall shielding are adopted to form high-speed cables. High-speed cables have excellent attenuation performance, low delay, and anti-interference ability, can achieve high-frequency broadband transmission, have specifications ranging from 32 to 24 AWG and multiple structures such as 2P, 4P, 8P, or 16P, and can be applied in various application scenarios.

Advantages of DAC High-Speed Cables:

They have become the preferred solution for users in short-distance application scenarios and are widely used in data center interconnection scenarios such as SATA storage devices, RADI systems, core routers, and 10G or 40G Ethernet. In data centers, copper cables are generally used to connect servers and storage area networks. Because passive copper cables are cheap and have fast transmission speeds, they have become the best solution for short-distance transmission.

High performance:

Suitable for short-distance wiring in data centers, with a wide range of applications and strong integration scheme switching capabilities.

Energy conservation and environmental protection: The internal material of high-speed cables is copper core and copper cables have good natural heat dissipation effects, which are energy-saving and environmentally friendly.

Low power consumption: High-speed cables have low power consumption. Since passive cables do not require a power supply, the power consumption of active cables is generally about 440 mW.

Low cost: The price of copper cables is much lower than that of optical fibers. Using high-speed cables can greatly reduce the wiring cost of the entire data center.

AEC High-Speed Cables

Technical Principle:

Active electrical cables add CDR (Clock Data Recovery) and Retimer chip architectures at both ends of the cable to not only amplify and equalize the transmission signals but also reshape the signals, thereby extending the transmission distance. They are suitable for application scenarios that require long-distance, low-power consumption, and compact design.

Basic Structure of High-Speed Cables:

They mainly consist of core wires with silver-plated conductors and Teflon insulating materials. Then, wire pair shielding and overall shielding are adopted to form high-speed cables. High-speed cables have excellent attenuation performance, low delay, and anti-interference ability, can achieve high-frequency broadband transmission, have specifications ranging from 28 to 24 AWG and multiple structures such as 8P and 16P, and can be applied in various application scenarios.

Advantages of AEC High-Speed Cables:

AEC active cables are released by the HiWire Alliance. The HiWire AEC specification defines the standards for basic electrical and mechanical specifications. AEC active cables support transmission rates of 100G, 200G, and 400G, and packaging types include QSFP56, OSFP, and QSFP-DD. The longest transmission distance can reach 7 meters. They have the forward error correction (FEC) function and cable re-timing function, which can ensure fully equalized signals with an ultra-low bit error rate.

AEC active cables are the key enabling technology for the DDC (Distributed Chassis) architecture. They overcome the density, weight, and performance limitations of copper cable DAC and the cost and availability issues of AOC. Their advantages lie in low power consumption, low cost, and space-saving. The power consumption is 25% lower than that of optical devices, the cost is 50% lower than that of optical components, the volume is smaller than that of DAC, and they can save up to 70% of space compared to DAC. Moreover, they are more reliable than optical ones.

AEC active cables are mainly used for the connection between ToR and servers and distributed chassis. Each rack can be wired with up to 500 cables. They are suitable for application scenarios that require long-distance transmission, low power consumption, and compact design, such as the interconnection needs of distributed data centers, and the telecommunications and enterprise markets.

• Power Consumption: The power consumption of both AOC and AEC is lower than that of DAC, which helps to reduce the overall system energy consumption.
• Transmission Distance: The transmission distance of DAC is limited, usually within 5 meters. AEC can extend the transmission distance to longer application scenarios through signal enhancement technology.
• Price: AOC has a higher price due to the inclusion of lasers and optical fibers. DAC and AEC are relatively cheap and suitable for large-scale applications.
• Size and Weight: The volume and weight of AOC and AEC are smaller than those of DAC, making them more suitable for application scenarios with limited space.

AOC High-Speed Cables

Technical Principle:

AOC active optical cables refer to communication cables that need to convert electrical signals into optical signals or vice versa with the help of external energy during the communication process. The optical transceivers at both ends of the optical cable provide photoelectric conversion and optical transmission functions. They look similar to copper cables. AOC uses an optical cable to connect two high-density connectors. AOC contains lasers inside and is relatively expensive, but has superior transmission performance.

Basic Structure of High-Speed Cables:

According to different application scenarios and requirements, the detailed structure and components of AOC high-speed cables may vary. For example, some AOC cables may also contain other auxiliary devices such as optical amplifiers and optical attenuators to optimize signal transmission and ensure system stability. In general, the basic structure of AOC high-speed cables consists of optical fibers, photoelectric converters, and connectors.

Advantages of AOC High-Speed Cables:

Firstly, they are much lighter than the other two types of high-speed cables. Secondly, since optical fibers are dielectrics, they are not easily affected by electromagnetic interference and are suitable for applications with long-distance and high-reliability requirements, such as the connection between core switches and long-distance transmission within data centers.

Disadvantages of AOC High-Speed Cables:

Compared with high-speed cables, the cost of active optical cables is relatively high. The lifespan of the lasers in AOC optical cables is generally 3 to 5 years, and they are difficult to repair. As a new type of transmission optical cable, active optical cables need to convert electrical signals into optical signals or vice versa with the help of external energy during the communication process. The losses in the conversion process and the heat energy losses generated are important reasons why AOC is difficult to popularize at present. However, many people in the market think that AOC optical cables have a longer transmission distance and reduce electromagnetic interference, so the advent of AOC has caused the misunderstanding that this newer technology should be adopted in all aspects of the network.

ACC High-Speed Cables

Technical Principle:

ACC (Active Copper Cable) is a kind of active copper cable. It adds a certain linear Redriver at the receiving end (Rx end) of the cable to provide signal equalization and shaping. It uses chips to compensate for the high-frequency losses of passive copper cable DAC and is more like an active cable that amplifies analog signals. It extends the transmission distance of traditional copper cables to a wider range of application scenarios. ACC can also be used to connect ToR and servers. It provides an economical and efficient way for short links, thus providing greater bandwidth transmission. The transmission distance of ACC can exceed 3m in high-speed transmission. Choosing the correct cable length is very important because it may be a key variable for overall performance.

ACC active copper cables support transmission rates and packaging types such as 10G SFP+, 25G SFP28, 40G QSFP+, 50G QSFP+, 100G QSFP28, 200G QSFP-DD, 400G OSFP, 800G OSFP, 400G QSFP DD, and 800G QSFP-DD.

ACC is mainly used in scenarios that require signal amplification and reduction. The transmission distance is relatively short, and it does not have repair and reshaping functions. Its market space is relatively small, but it still has applications in some scenarios that are sensitive to cost and do not have high requirements for transmission distance.

Summary: DAC, AEC, AOC, ACC

When choosing data transmission cables, comprehensive considerations should be made according to specific application requirements, transmission distance, cost budget, and space limitations. In the field of data communication, we have seen the application trend of Ethernet emerging. ACC is expected to expand from Infiniband to Ethernet applications. We believe that the upgrade of switch rates is also expected to drive changes in high-speed connection methods in data centers. New products such as AEC and ACC are expected to expand downstream customers. We think that the emergence of higher-speed switches is expected to drive the upgrade of port rates. Traditional copper cable DAC is prone to huge losses and attenuation of transmission signals at high speeds. To compensate for signal attenuation, the diameter of DAC needs to be continuously increased. According to Amazon, the outer diameter of a 100G-rate DAC that supports a 2.5-meter transmission is 6.7 mm, while the outer diameter of a 400G-rate DAC that supports a 2.5-meter transmission reaches 11 mm, making it more difficult for cloud vendors to arrange data cables. In addition, the larger outer diameter of DAC also means a larger bending radius, resulting in a larger floor area and occupied space of the entire rack. Currently, the innovative solution for high-speed copper connections is the active cable AEC. Compared with DAC, AEC adds chips at both ends of the copper cable to recover signals and can reduce the losses and attenuation generated when high-speed signals are transmitted through copper wires. Therefore, the outer diameter of AEC is smaller than that of traditional DAC, and the occupied space is also lower. In the construction of large-scale AI clusters, we believe that due to the significantly increased interconnection density of AI clusters compared to cloud computing, AEC with its smaller outer diameter is more suitable for large-scale networking wiring. In addition, short-distance transmission, compared with optical communication solutions using optical modules and optical fibers, AEC has the advantages of low cost, low energy consumption, and low maintenance cost. According to Credo's calculation, the comprehensive cost of 400G AEC can be reduced by 53% compared to the AOC solution. We believe that in the future, as the network transmission rate in data centers continues to increase, DAC will face greater difficulties in short-distance transmission, and innovative connection methods such as AEC are expected to replace DAC. According to Lightcounting's estimate in December 2023, the markets of AOC, DAC, and AEC were 12 billion US dollars in 2023 and are expected to reach 28 billion US dollars in 2028, with the CAGR of AOC, DAC, and AEC from 2023 to 2028 being 15%, 25%, and 45% respectively.