DAC vs AOC: Understanding the Differences

In the world of data centers, short-range server interconnects and server-to-switch connections are crucial.

Two key players in this arena are Active Optical Cables (AOC) and Direct Attach Cables (DAC).

While both are integral to modern network infrastructure, they serve different purposes and come with distinct features.

Let's delve into what sets AOC and DAC apart.

What is an Active Optical Cable (AOC)?

Active Optical Cable (AOC) is a cabling technology that uses optical fiber between the connectors to improve the transmission of data.

In the realm of data centers, high-performance computing, and large-capacity storage devices, AOCs are prized for their high-speed and high-reliability interconnect capabilities.

They typically comply with industry-standard electrical interfaces and perform electrical-to-optical-to-electrical conversions internally, capitalizing on the superior qualities of optical fibers for data transmission.

AOCs consist of two optical transceivers connected by a fiber optic cable.

The optical transceivers house circuit boards with optical transmitters and receivers that convert electrical signals into optical signals and vice versa.

Optical fibers allow for longer transmission distances (up to 300 meters), but AOCs tend to be more expensive and consume more power than DACs due to their complex design and manufacturing processes.

What is a Direct Attach Cable (DAC)?

Direct Attach Cable (DAC), sometimes also referred to as a direct-attach copper cable, is a form of cable that transmits electrical signals over copper wire.

Unlike AOCs, DACs do not involve conversions between electrical and optical signals.

There are two main types of DACs: passive and active.

  • Passive DACs are shielded high-speed copper cables with SFP connectors on each end and without any signal processing chips. They are known for their low cost, ultra-low power consumption (less than 0.1 watts), and high reliability but are limited to short distances (usually less than 10 meters).
  • Active DACs, while similar to passive ones, include signal compensation chips for pre-emphasis and equalization to boost signal strength over longer distances.

AOC vs DAC: Key Differences


 

  1. Power Consumption: AOCs typically consume between 1W to 3W of power, whereas active DACs generally consume less than 500mW, and passive DACs, with their special heat dissipation design, can consume as low as 0.15W, nearly zero power consumption.

  2. Transmission Distance: AOCs have a longer transmission range (up to 100 meters for OM3 cables) compared to DACs, which usually max out around 7 meters. The maximum distance for DACs can vary with the data rate; higher rates often mean shorter distances.

  3. Transmission Medium: AOCs use optical fibers (insulating) and are immune to electromagnetic interference, while DACs are made of copper and are susceptible to such interference.

  4. Signal Transmission: AOCs transmit optical signals, whereas DACs carry low-voltage pulse electrical signals.

  5. Cost: Optical fibers are generally more expensive than copper, and AOCs also include laser devices at both ends, resulting in higher costs compared to DACs.

  6. Size and Weight: At equal lengths, AOCs weigh about a quarter and take up about half the volume of DACs, making them easier to manage and transport.

  7. Transmission Performance: AOCs generally have a lower bit error rate than DACs.

  8. Components Used: DACs do not contain optical components, whereas AOCs include lasers.

For those looking to equip their data centers with the appropriate AOC and DAC solutions, Fibeye is ready to assist.