Unveil the mysteries of direct attach cable

Nowadays, an indisputable fact can be found in today’s telecommunication market that no matter which country, data center, call center, business or industry, the requirements of bandwidth, and data storage are always increasing, users are always looking for high-quality cables to meet these needs, which also makes the technology manufacturers have to continue to develop and launch faster and better technology. As a mature technology, direct attach cable comes to be popular, which provides 25Gbit/s, 50Gbit/s and 100Gbit/s pre-terminated solution. Maybe you are not familiar with them, but do not worry, now, let us unveil the mysteries of direct attach cable!

First of all, let us know about the basic information of direct attach cable.

Definition of Direct Attach Cable

Direct Attach Cable is called DAC for short which refers to the high-speed jumper installed optical module at both ends, and by connecting the switch to the router or server, is a kind of optical transceiver components and one form of high speed cable. DACs are much cheaper than conventional optics because the “transceiver” at both ends is not true optical device. Due to low cost, low power consumption and high performance, they are the first choice for Storage area network, data center and high performance computing connectivity.

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Application of Direct Attach Cable

Direct attach cables are ideal choice for high-density, high-speed I / O data center applications in the networking, telecommunications and data storage markets, which require the highest overall network efficiency and lower overall cost. Direct attach cable is widely used in storage area network, data center and high-performance computer connection, and become to be a rising star in the network communication.

Certainly, this is no doubt that the huge network communication system must have different demands for DAC according to different needs and applications, so DAC have different types to meet these different requirements. Here we’ll explain the most common types of DAC in detail.

Types of Direct Attach Cable

Direct attach cable can be divided into several types based on different standards. 10G SFP + cable, 40G QSFP + cable and 120G CXP cable are provided via Ethernet transmission rate and construction standards. It is also possible to classify according to the number of connectors. Most of DAC assemblies have a connector at each end of the cable, but there is a special type of DAC assembly that can have three or four connectors at one end of the cable. Taking QSFP+ to 4 * SFP+ passive copper DAC as an example, it has a QSFP+ connector (SFF-8436) at one end which rate is 40G/s, the other end is 4 * SFP+ connectors (SFF-8431)which rate is 4 * 10G/s. From the point of the material of the cable, DAC can be classified into direct attach copper cable and active optical cable (AOC). Direct attach copper cable can also include passive or active, but the AOC cable is always active. The diagram bellow shows that the main types of passive and active cable in the data center.

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As two types of commonly used transceiver assemblies, direct attach copper cable and AOC have its pros and cons. The following parts will be used for describing the features and application in detail, So that when you choose the DAC to know which one is the best and the most suitable for your needs.

Selection of DAC

Direct Attach Copper Cable

Direct attach copper cable have two versions: active and passive. The former provides signal processing electronics to avoid signal problems, so that to improve the quality of signal. Moreover, the former has a longer distance to transmit data than the latter, which provides a direct electrical connection between corresponding cable ends. Currently, because of its interchangeability, low cost and a variety of data rates still have a place in the market. With the development of fiber technology, some people think that the copper technology is out of style, but you need to change the idea for direct attach copper cable. In fact, direct attach copper cable still has its advantages in the market.

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Advantages of Direct Attach Copper Cable

  • Data rates for all applications: today’s direct attach copper cable can support higher transmission rate than traditional copper interface, from 4Gbps to 10Gbps per channel
  • Interchangeability – With the development of copper technology, direct attach copper cable can be interchangeable with fiber modules and hot-swappable.
  • Cost-effective: supports Gigabit and 10 Gigabit Ethernet, 8G FC, FCoE and infiniBand and other protocols, direct attach copper cable is a cost-effective solution for optical transceivers.

Disadvantages of Direct Attach Copper Cable
Direct attach copper cable is heavy and bulky, making it difficult to manage. In addition, due to the nature of the electrical signal, direct connection of copper cables is susceptible to electromagnetic interference (EMI), such as undesired response, degradation or complete system failure.

Active Optical Cable

Active cable (AOC) is a type of DAC. It integrates multimode fiber, fiber optic transceivers, control chips and modules. It adopts electrical-to-optical conversion at the cable end to increase the performance of cable speed and distance when matched to the electrical interface standard. AOC is a replacement for optical transceivers that eliminates the separable interface between the transceiver module and the fiber optic cable. It offers many advantages over direct attach copper cable. Such as smaller volume, anti-electromagnetic interference, lower interconnection losses, longer transmission distance etc. allow it to have a good reputation among consumers.

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Advantages of AOC

  • Higher bandwidth: no requires for device upgrade, the throughput of QSFP + of up to 40 Gbps.
  • Lightweight: AOC is lighter than direct attach copper cable due to its material.
  • EMI anti-interference: as the fiber is a dielectric (cannot conduct current), AOC is not affected by electromagnetic energy

Disadvantage of AOC

Compared with direct attach copper cable, the costs of AOC stay at high level.

Now, we’ve learnt the basic information of DAC, but it is not much enough for a deeper understanding of DAC. We’d better to know the application and working principle of DAC in the actual network practice. Here we will introduce the data center interconnection by using DAC assembles.

Use Direct Attach Cable Assemblies for Data Center Interconnection

DAC assembles includes DAC, direct attach copper cable and AOC, mainly used as media to support high transmission rate between servers, switches and storage devices intra rack or inter rack in a data center. Due to the direct attach cable assemblies use the same port as an optical transceiver, and the cost and power can be saved in short-distance applications, they are very popular among data center operators.

Direct attach copper cable assembles

Direct attach copper cable can achieve the interconnection of up to 7 meters in the case of 10G, 40G and low power.

Direct attach active copper cable

Direct attach active copper cable is designed for the same cable type as passive cable, but contains active assembles to boost / receive signals that require more power. It can reach 15 meters in 10Gbps or 40Gbps.

Active optical cable

AOC is designed for fiber type, it includes active electrical and optics, can achieve longer distance than copper assembles, which can reach over 100 meters by using multimode fiber.

What’s more, uses fan-out technology, both direct attach copper cable and AOC can be designed for breakout direct attach cable assemblies. For instance, 40G QSFP+ to 4 * SFP+ AOC, can better meet the needs of network migration.

The case of DAC assembles

DAC assembles are the ideal choice for the short-distance direct attach application. Usually they are used in EDA (Equipment Distribution Area), where cabinets and racks house end equipment (servers) and where horizontal cabling from the HDA (Horizontal Distribution Area) is terminated at patch panels, the figure bellow shown the details.

For the interconnection between racks and rack rows, DAC assembles can be used for connecting server to switch, storage switch or switch to switch, Uses direct attach copper cable or active copper cable, active optical cable or breakout cable assembles with different length options based on different interconnect applications and distance requests.

For the reason of 10G network are widely deployed in today’s data center, 10G SFP+ DAC commonly used in interconnect application less than 15 meters. For example, server to switch or storage to switch interconnection in the same rack. Now 25GbE is popular and recommend replacing the 10G network in the future. 25G DAC assembles like SFP28 has been selling on the market. As for 40GbE, using 40G QSFP+ DAC and AOC, the former usually used in short-interconnection under 15 meters, and the latter is used for longer interconnect application(15m-100m). Spine switches are needed for higher speed and more bandwidth, so that 100G DAC like QSFP28 are recommended to use in this situation. The following picture indicates the data center interconnection with direct attach cable assemblies.


So far, do you have a better and clearer understanding of direct attach cable? Direct attach cable provides greater bandwidth with a cost-effective way. Which type of DAC suitable for network connecting depends on the specific condition. Cozlink offers high quality DAC mentioned above, and also offers the product customization service to satisfy the different needs of yours, please feel free to visit our official website if you want to learn more: https://www.cozlink.com/ We are ready to help.