How to choose 400G DAC & 400G AOC?

NADDOD Jason Data Center Architect Aug 2, 2023

Due to the continuous growth in demand for data center and cloud computing resources, it has driven the development of ultra-large-scale public cloud data centers. Global data traffic continues to rise, prompting data centers to develop towards higher speeds, larger bandwidths, and lower latency, making 400G Ethernet the inevitable trend for data centers. In order to meet the interconnection needs within and between racks in data centers, enterprises, and high-performance computing environments, 400G DAC and AOC cables have become the main choices for short-distance interconnection due to their low power consumption, high stability, fast response, and easy installation.


The following are the main types of 400G DAC and 400G AOC classifications currently available on the market:

Package type:

QSFP-DD: the most mainstream packaging mode in 400G data centers, which is a common packaging type for 400G DAC and 400G AOC, using the 8*50Gb/s PAM4 electrical modulation format.

OSFP: another packaging type used for 400G DAC and 400G AOC, also using the 8*50Gb/s PAM4 electrical modulation format.

Cable type:

DAC: Direct Attach Cable, commonly known as DAC, refers to copper cables used for direct connection without the need for optoelectronic conversion to transmit electrical signals. It is the preferred option for short-distance applications and is widely used for data transmission between servers within or between adjacent racks in data centers. Its biggest advantage is its low cost, ultra-low power consumption, and high reliability.

AOC: Active Optical Cable, commonly known as AOC, refers to active optical cables. There are optical transmitters and receivers on the circuit board of the modules on both ends of the AOC cable, which convert electrical signals into optical signals at the transmitting end, transmit them through the fiber, and convert them back into electrical signals at the receiving end. Due to the use of optical signal transmission, it can transmit over longer distances than DAC. However, due to the complexity of design and processing technology and the need for optoelectronic conversion, its cost and power consumption are higher than that of DAC.

Direct connection and breakout:

Direct connection cable: both ends are fixed QSFP-DD packaged optical modules, connected by optical fibers or copper cables in between.

Breakout cable: one end of the cable uses a 400G connector, and the other end uses several identical low-speed connectors, with a total rate of 400G. It is suitable for scenarios that require distributing a high-speed optical signal to multiple devices.