25G SFP28 DAC vs AOC: Overview

Updated on Oct 28, 2021

25G SFP28 Passive DAC

25G DAC & AOC are the ideal and cost-effective solutions for short-distance connectivity within a rack or between adjacent racks in 25G data transmission. What are 25G DAC and 25G AOC? What are the differences between them? The following will guide you through an overview of 25G DAC and AOC to help you find the right cabling solution for your network.

An Overview of 25G DAC vs AOC

Definition and Type

There are two types of 25G DAC high-speed cables available in the market, which are 25G SFP28 Direct Attach Copper Cable and 25G SFP28 Active Optical Cable. Both cables offer optical inter-connectivity for short-distance and can transmit data at a speed of 25Gbps.

25G DAC cable, a high-speed copper cable, is designed with an insulation core and twin-axial copper cable with the SFP+ form factor and two modules, one at each end. It is designed to offer low latency, high attenuation performance, and more bandwidth in data centers.

25G AOC is another cost-effective, reliable alternative to traditional, costly optical transceivers. This cable is an amalgamation of optical components and electronics or active electrical components. Similar to an active DAC, the 25G AOC uses two strands of optical transceiver assemblies in bi-directional transmission mode. It uses a fiber cable and silicon chip and provides an electrical-to-optical connection to boost the signal and performance of the cable.

25G DAC vs AOC: Weight & Bending Radius

Using fiber optic cable as transmission media, 25G AOC has much smaller size and lighter weight when compared with 25G DAC. So it can be flexibly deployed in places where space is a premium, and can be transported from one place to another. Also, the bending radius of 25G SFP28 AOC is significantly smaller than 25G DAC, which makes 25G AOC cable more suitable for high-density cabling structures.

SFP28 DAC vs AOC: Heat Dissipation & Power Consumption

The basic 25G DAC is passive and has less power consumption or heat producing, thus making it a more versatile with wider temperature ranges. Moreover, its cooling requirement is not strict due to the thermal design, so applying 25G DAC can significantly save the data center operating expenses. 25G DAC will keep the transmission stability even in harsh natural conditions and external interference.

25G DAC vs AOC: Electromagnetic interference (EMI)

Since the cable type of 25G SFP28 AOC is fiber, it is immune to interference from electromagnetic, lightning, or radio signals during data transmission. The 25G DAC might be susceptible to electromagnetic interface, such as adverse response and degradation, etc, but the impact is not significant. If there are special requirements for the EMI in the network, the 25G AOC will be an ideal solution to ensure good confidentiality during the transmission, which can be applied for secure transmission in large data center networks.

SFP28 DAC vs AOC: Price

The price of the 25G AOC is often more expensive than that of 25G DAC. For transmission within 5m, DAC is evidently more cost-effective, especially when deployed in large data centers. When the transmission distance exceeds 5m, the SFP28 AOC or 25G modules with structured cables are the better solutions.

25G DAC vs AOC: Application Scenarios

Direct attach cables can be used in a variety of applications and locations in a data center. In general, this pre-terminated solution is particularly effective for the following applications:

Top of Rack (ToR)/Adjacent Rack: 25G direct attach cables are ideal for shorter ToR or rack-to-rack runs with cost-conscious budgets.

Middle of Row (MoR): since the 25G DAC cable can run no more than 5m, they may be the perfect solution in the MoR applications.

End of Row (EoR): 25G AOCs are most likely the best option for EoR configurations since the applicability of the 25G DACs reaches their limit at around 30m in length.

Zone-to-Zone: 25G SFP28 AOC is the clear solution for longer zone-to-zone runs due to the advantages of using fiber optic cables as mentioned previously.

FAQs about SFP28 DAC vs AOC

The following are some frequently asked questions concerning 25G direct attach cables.

Q: What’re the benefits of 25G direct attach cables?

A: For starters, 25G direct attach cables are less costly than using discreet transceivers with field-connected structured cabling because the interconnection is simplified. There aren’t as many connectors, adapters, patch panels, and other infrastructure elements along the path of the communication channel. Secondly, DACs, particularly passive DAC cables, have lower power consumption compared to transceivers, because they have self-contained components and are not bound by transmission specifications as transceivers. Moreover, DACs and AOCs offer plug and play simplicity.

Q: Can 25G DAC/AOC be backward compatible with 10G or 1G?

A: The 25G AOC cables can support backward compatibility with 10G/1G. But whether 25G DAC cable can be backward compatible is determined by the brands of the networking device.

Q: Can I have different compatibilities for each end of 25G direct attach cables?

A: Of course, different compatibilities for each end of 25G direct attach cables can be provided on the market. FS.com offers customized dual compatibility solutions for 25G direct attach cables so that you can choose compatibilities for each end individually. All you need to do is to select the "Dual Compatibility Solutions" option in Compatible Brands drop-down box and note down your devices’ model numbers on the custom page.

Q: How to choose a reliable supplier for 25G direct attach cables?

A: Technology, quality, compatibilities, technical support, warranty policy, and after-sale services are needed to be considered when choosing a reliable supplier. A trustworthy supplier should provide comprehensive customer services, return and exchange services, professional technical support, product testing, warranty services, etc.


Both 25G DAC and AOC cables are cost-effective and ideal solutions for short-distance transmission between rack and rack in a data center. They are widely applied in storage area network, data center, and high-performance computing connectivity, etc. AOC vs. DAC: the correct choice can be made when you are clear about the advantages and disadvantages of each. When it comes to the transmission distance over 100m, 25G fiber optic transceivers combined with matched optical fiber cables are more common and efficient solutions.

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