Direct Attach Cable VS. Active Optical Cable

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Date: 2023-01-31 14:03:34

　Direct attach cable (DAC) and active optical cable (AOC) is crucial high-speed interconnect cabling solutions in data centers and high-performance computing applications. DAC and AOC cables are plug-and-play, allowing the users to optimize the existing network without new optical fiber cabling. This article will discuss the differences between DAC and AOC cables.

DAC Cable VS. AOC Cable

DAC cable consists of a Twinax copper cable terminated with SFP+/SFP28/QSFP+/QSFP56/QSFP28 connectors on both ends, which can provide an electrical connection directly to active equipment. DAC cable can be passive or active. Passive and active DAC cables can transmit electrical signals directly over copper cables. The passive DAC cable can deliver without signal conditioning, while the active DAC cable has electric components inside the transceivers to boost signals. AOC cable consists of a multi-mode fiber optic cable terminated with SFP connectors on both ends, which requires external power to complete the conversion of electric and optical signals, from electric signals to optical ones, and then convert to electric signals finally.

DAC and AOC cables differ from each other in the following aspects :

1. Power Consumption

Usually, the power consumption of an AOC cable is higher than a DAC cable, which is 1-2w. While the power consumption of active DAC cables is less than 1w, and the passive DAC cables cost nearly no power consumption at the value of lower than 0.15w due to the thermal design of DAC cables. As a result, the operating expenses on power consumption will be decreased when adopting the DAC options.

2. Transmission Distance

AOC cable can transmit over longer distances up to 100 m, while DAC cable link length limit is 10 m (passive DAC: 7 m; active DAC: 10 m). To sum up, DAC cable is suitable for short-range transmissions, while AOC cable is used for long-range transmissions.

Note: the max. distance of a signal that can be transmitted via a DAC cable changes depending on the data rate. The link length will decrease as the data rate grows, for example, 100G DAC cables can only transmit up to 5 meters.

3. Cost

In general, copper cables are much cheaper than fiber cables. When implemented in the high-density data center, the sum of money will be saved for large quantities of DAC cable compared to AOC cable.

4. Electromagnetic Interference Immunity

AOC cable is immune to electromagnetic interference, while DAC cable is vulnerable to the effect of electromagnetic interference, such as unwanted responses, degradation, or complete system failure.

5. Application

DAC cable is used to connect switches/servers to switches within racks and adjacent racks. In other words, DAC cable is used as an alternative for ToR (top of rack) interconnections between the ToR switch and server or the stacking of switches.

AOC Cable is used to connect ToR switches to EoR (end-of-row) aggregation switches, and to connect the ToR switch with MoR (middle-of-row) storage subsystems at reaches greater than DAC cable limits of 3-7 meters.

Conclusion
DAC and AOC cables are simple, cost-effective cabling solutions that are designed for the same ports as SFP+ or QSFP transceivers. DAC cable use copper-based cabling while AOC cable use fiber-based cabling. DAC cable provides lower power consumption and is cheaper than AOC cable. However, AOC cable provides long transmission distances than DAC cable. Sun Telecom specializes in providing one-stop total fiber optic solutions for all fiber optic application industries worldwide. Contact us if any needs.

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