AOC VS. DAC: Which One Is Better For Your Needs?

• Understanding of Active Optical Cable（AOC）

• Understanding Direct Attach Cable (DAC)
  

• AOC/DAC Comparison

Understanding of Active Optical Cable (AOC)

What is Active Optical Cable, AOC?

Let's start with AOC, which stands for Active Optical Cable. AOC consists of two modules at both ends, connected by a section of optical fiber in the middle. The optical module and the optical cable are integrated, and the optical modules at both ends require laser components.

AOC classification

10G SFP+ AOC

25G SFP28 AOC

40G QSFP+ AOC

40G QSFP+ to 4xSFP+ AOC

100G QSFP28 AOC

100G QSFP28 to 4xSFP28 AOC

100G QSFP28 to 2x50G QSFP28 AOC

200G QSFP56 AOC

200G QSFP28-DD to 2xQSFP28 AOC

400G QSFP-DD AOC

400G QSFP-DD to 4xQSFP56 AOC

I believe you have found out. There is a scenario where 40G can be divided into 4x10G, 100G can be divided into 4x25G or 2x50G QSFP28 AOC; 200G can be divided into 2*100G and 400G can be divided into 4x100G. This allows one high-speed port to be converted to four low-speed ports, facilitating the interconnection of switches with ports of different speeds.

AOC advantages and application scenarios

Compared with other cables, AOC has many advantages. It provides high transmission rates, long-distance capabilities, low power consumption, light weight and ease of use. These benefits are achieved by adopting optical transmission, which overcomes the limitations of passive optical fiber cables or other cable types.

Due to its lightweight and compact design, AOC is becoming increasingly popular in data centers and high-performance computing (HPC) applications. Traditional copper-based technologies are being phased out because they tend to be heavy, bulky and inefficient. In data centers with limited space, AOC meets the requirements of high-density connections. In addition, copper cables are susceptible to electromagnetic interference (EMI), which hinders data transmission speeds and increases packet loss. Therefore, AOC active optical cables are ideal for IDC data centers, HPC environments, and InfiniBand quad-switch interconnections.

Disadvantages of AOC

Having said that, there are pros and cons to consider. The AOC optical port remains hidden, so there is no need to clean the port or worry about contamination. This greatly improves the stability and reliability of the system. However, the disadvantages of AOC are also obvious in this regard. Since the A0C module is directly connected to the cable, if there is a failure, the entire module needs to be replaced, which is a major disadvantage compared to the optical module + jumper connection.

Understanding Direct Attach Cable (DAC)

What is Direct Attach Cable (DAC)?

DAC, also known as Direct Attach Cable, is a high-speed cable made of silver-plated copper conductors and foam-insulated wire. The ports of this cable are not replaceable, and the module head and copper cable cannot be separated.

DAC cables can be divided into two types: passive copper cable (PCC) and active DAC.

Active DAC can be further divided into active copper cable (ACCQ) and active cable (AEC), which will be explained later! Both passive and active DAC cables can transmit electrical signals directly over copper wires. The former can transmit without signal conditioning, and the latter is equipped with electronics inside the transceiver to enhance the signal. Unless otherwise specified, when DAC is mentioned below, it refers to PCC.

Characteristics and Applications of DAC

DAC does not contain a photoelectric converter module, and the cable end consists of a simple cable connector. This makes them highly cost-effective. In data centers, copper cables are often used to connect servers and storage area networks. Due to its affordability and high-speed performance, passive copper wires have become the best solution for short-distance transmission, and the main application scenarios are concentrated in interconnections within 5 meters/10 meters.

DAC classification

10G SFP+ DAC

25G SFP28 DAC

40G QSFP+ DAC

40G QSFP+ DAC

40G QSFP+ to 4x SFP+ DAC

100G QSFP28 DAC

100G QSFP28 to 4xSFP28 DAC

100G QSFP28 to 2x50G QSFP28 DAC

200G QSFP56 DAC

200G QSFP28-DD to 2x QSFP28 DAC

400G-DAC-QSFP-DD

400G QSFP-DD to 2x QSFP56

400G QSFP-DD to 4xQSFP56 DAC

DAC is the same as AOC. 40G can be split into 4x10G, 100G can be split into 4x25G100GQSFP28, 2x50GQSFP28DAC; 200G can be split into 2*100G400G can be split into 4x100G. Convert a high-speed port into 2 or 4 low-speed ports. To facilitate the interconnection of switches with ports of different speeds.

Advantages and Disadvantages of DAC

Advantages:

High-speed transmission: DAC data cables generally support data transmission rates of up to tens of Gbps, providing faster bandwidth and transmission speeds compared to traditional copper and fiber optic cables. 

Cost-effectiveness: Compared to fiber optic modules and cables, DAC data cables are generally more affordable and are a cost-effective solution for high-speed connections, especially over shorter distances. 

Low power consumption: Unlike fiber optic modules that rely on the photoelectric conversion process, DAC data cables have relatively low power consumption in transmitting electrical signals, which helps reduce the energy consumption of the entire system. 

Efficient heat dissipation: Copper core high-speed cables have excellent heat dissipation capabilities, ensuring effective cooling.

Disadvantages:

Distance limitation: Because DAC data cables rely on copper wire media, they are limited in terms of the distance of electrical signal transmission. They are mainly suitable for short-distance connections (less than 7 meters) and are not suitable for long-distance transmission.

Limited flexibility: DAC data cables are generally bulky and rigid, lacking the flexibility of fiber optic cables. Therefore, they are not suitable for applications involving frequent bending or bending. Susceptibility to electromagnetic interference: Because DAC data cables use copper cable media, they may be susceptible to electromagnetic interference, especially in high-density wiring environments. This interference may affect the stability and reliability of data transmission.

AOC/DAC Comparison