A Brief Introduction to 400G DAC and 400G AOC

The exponential expansion of network and data traffic has fueled a sharp uptick in the demand for 400G optical transport technologies. QSFPTEK addresses this demand by introducing the 400G QSFP-DD DAC and 400G breakout DAC cable, ideal for ultra-short-haul applications in data center interconnect (DCI). These solutions provide strong performance, dependability, and adaptability, meeting the requirements of data centers, enterprises, and high-performance computing environments. This article will explore the fundamentals of 400G DAC and 400G AOC technology, exploring their unique characteristics and addressing frequently asked questions regarding their deployment and functionality.

What is 400G DAC and 400G AOC?

 

The 400G DAC is perfectly suited for ultra-short-range data center interconnections, presenting a budget-friendly solution. Utilizing copper cables as the transmission medium, DACs come in two main types: passive copper cables for distances ranging from 0 to 5 meters and active copper cables for distances spanning 5 to 15 meters.

 

 

400G AOCs use optical fiber for transmission, delivering performance with transceivers. Unlike DACs, 400G AOCs support longer distance transmissions of up to 100 meters. They are also lighter and more compact, albeit at a higher cost. Additionally, AOCs are not susceptible to Electromagnetic Interference (EMI).

 

Both 400G DAC and 400G AOC are available in two primary form factors, QSFP-DD and OSFP, and they both support 8x50Gb/s PAM4 electrical lanes. Additionally, there are 400G breakout DAC/AOC cables, featuring a 400G connector at one end and several identical connectors, totaling 400G, at the other end. The table below illustrates the critical types of 400G DAC/AOC and the currently available 400G breakout DAC/AOC cables.

 

 

What is the Difference Between 400G DAC and AOC?

 

Based on the data, the primary variances between 400G DAC and 400G AOC lie in transmission distance and market availability. 400G DAC offers more breakout cables and caters to diverse connection needs. Additionally, they diverge in several key aspects:

 

Transmission Medium: 400G DAC employs copper wires to transmit signals through electrical currents, whereas 400G AOC uses optical fibers to transmit signals via optical pulses.

 

Transmission Distance: 400G DAC is ideal for short-range connections within a cabinet or between racks, whereas 400G AOC facilitates longer-distance transmission, reaching up to 100m, typically utilized for inter-cabinet connections in data centers.

 

Weight and Size: 400G AOC, employing fiber optic cables, occupies roughly half the volume and weighs a quarter of 400G copper DAC, featuring a smaller cable bending radius.

 

Interference-Resistance: Unlike 400G DAC, which is susceptible to electromagnetic, lightning, or radio signal interference during data transmission, 400G AOC, being non-conductive, provides resistance to such disruptions.

 

Price: Presently, 400G AOC often commands a higher price than 400G DAC of equivalent quality on the 400GbE cable market. Therefore, if both options meet your requirements, selecting 400G DAC may offer cost savings.

 

400G AOC vs. 400G DAC, How to Choose?

 

There are essentially three types of products used to interconnect data centers: optical modules, direct attach copper cables (DAC), and active optical cables (AOC). Industry experts typically prefer AOCs for their architectural advantages. DACs are often criticized for being bulky, challenging to manage and wire, and prone to electromagnetic interference from electrical signals. However, this doesn't imply that copper cables lack value altogether.

 

Indeed, copper cables offer their own set of advantages. Advancements in cable technology and manufacturing enable modern copper cables to support higher data transmission rates compared to traditional interfaces. Direct-attach copper cables are versatile, allowing for interchangeability and hot-swapping with optical modules and AOCs. In terms of cost-effectiveness, copper cables are more economical, and passive copper cables consume less power compared to their optical counterparts. These attributes contribute significantly to data center investment and operation while minimizing environmental impact.

 

When considering transmission scenarios, Optical modules and optical fiber have a wide array of applications, covering telecom convergence front propagation, medium propagation networks, and data center switches. AOC is well-suited for high-bandwidth interconnections covering the maximum transmission distance up to 100m, while DAC is ideal for linking servers and GPUs to top-of-rack switches.

 

When considering expenses, optical modules paired with optical fiber are pricier yet offer greater networking flexibility, remaining the predominant choice for international cloud vendors when considering overall expenses. Active Optical Cables (AOC) offer cost efficiency with their integrated design, whereas Direct Attach Cables (DAC) are the least expensive option since they don't necessitate optical-electrical conversion. Nevertheless, DAC's transmission range is significantly restricted at high speeds.

We anticipate that the shift towards "optical in, copper out" in telecom access networks will also manifest in data center interconnect networks. Historically, the high cost of high-speed optical modules rendered AOC solutions less advantageous. However, as the cost of these modules decreases, we expect the transition from DAC to AOC solutions to accelerate, particularly in the era of AI supercomputers.

 

The Factors You Need to Be Considered When Choosing 400G AOC and DAC

 

Transmission Distance: For longer transmission distances exceeding 3 meters, opting for a 400G AOC might be preferable.

 

Flexibility and Interchangeability:  If there is a frequent need for layout replacements or expansions, the 400G AOC offers enhanced flexibility.

 

Cost and Maintenance:  If there's a constrained budget or a need for straightforward installation and management, the 400G DAC might be a more suitable option.

 

Conclusion

 

In conclusion, the decision between 400G AOC and 400G DAC relies on specific requirements and prioritized criteria. In real-world scenarios, this decision is typically influenced by the data center's layout, budget, and performance demands. Additionally, selecting a trustworthy supplier is essential when procuring high-speed cable products. NADDOD stands out as a premier provider of optical network solutions, committed to crafting a connected world of smart devices through inventive computing and networking solutions.

FAQ About 400G DAC/AOC

 

Q: What is The PAM4 Modulation Method of 400G DAC and AOC?

 

A: PAM4 is more efficient than other modulation technologies, significantly enhancing bandwidth utilization. PAM4 signals operate at the same Baud rate as traditional NRZ signals and achieve twice the transmission speed, resulting in substantial cost savings in transmission.

 

Q: What standout technologies are present in 400G DAC and AOC?

 

A: The primary technologies utilized in 400G DAC/AOC are PAM4 and DSP. While PAM4, especially in 400G AOC, is more susceptible to noise compared to NRZ, DSP is incorporated to mitigate this drawback. The DSP technology functions as a high-speed digital processing chip, not only offering signal recovery capabilities akin to traditional CDRs but also assisting in dispersion compensation while eliminating noise, nonlinear disturbances, and other interferences.

 

Q: Can a 400G QSFP-DD DAC be inserted into an OSFP port?

 

A: No, it's not possible because they have different form factors.

 

Q: Can I plug a 400G QSFP-DD DAC into a QSFP28 port?

A: No, the 400G QSFP-DD DAC is not compatible with the QSFP28 port.