What Makes Direct Attach Cable Preferable for 40/100G Migration?

As new applications, devices and architectures continue to demand ever higher speed networks, 40G and 100G Ethernet links are rapidly coming on line. Many vendors have put forward various solutions for 40/100G migration, including optical transceivers (like QSFP+ or QSFP+ 28), fiber cabling (like MPO/MTP breakout cable or MPO/MTP harness cable), and copper cables (like direct attach cable). Among these solutions, direct attach cable with unique advantages is more preferable for 40/100G migration. But why? The following part will explain the reasons in details.

What Is Direct Attach Cable?

Direct attach cable (DAC), also known as twinax cable, is a fixed assembly supporting high data speed that uses a small form-factor connector module as an optical transceiver at the either end of a length of cable. Generally, direct attach cable can be active and passive. The former one has active electronic components in the optical modules to improve the signal quality, while the latter one is mainly just a straight “wire” and contains a few components. With low cost, low power consumption and low latency, DAC has become popular in network industry and widely applied in storage area network, data center and higher performance computing connectivity to achieve the migration to 40/100G. The image below shows Cisco QSFP-H40G-CU1M compatible 40G QSFP+ Passive Direct Attach Copper Cable.

Cisco QSFP-H40G-CU1M compatible 40G QSFP+ Passive Direct Attach Copper Cable

Unique Features of Direct Attach Cable

With many unique features, direct attach cable can satisfy the increasing demand for high speed data transmission. The main features of DAC are described in the following text.

  • Low Price—DACs are much cheaper than the regular optics. Because the “transceiver” on both ends of DACs are not real optics. Compared with regular optical transceivers, the small form-factor connector modules are without expensive optical lasers and electronic components, and they’re just used to transmit the optical signals. Accordingly, the cost of DACs will be much lower. Besides, DACs in some case can be an alternative to optical transceivers as it eliminates the separable interface between transceiver modules and optical cable. Thus, direct attach cable is a more cost effective solution for 40/100G applications.
  • Power Saving—A small electrical component is used in both active direct attach cable and passive direct attach cable to identify the modules on the end and cable type to the Ethernet interface. Compared to optical transceivers, DACs with this component consumes very litter power.
  • Enough Data Rate for Various Applications—With the appearance of optical fibers which can support high data speed and achieve good performance in networks, many people may think that copper has been out of sight. Actually, DAC can also provide high speed input and output data. Currently, DACs are most commonly used for 10G and 40G applications. And with the development of technology, some direct attach cable can be used to achieve data transmission of 100G, or even 120G.
  • Interchangeability—With the advancement of copper cable technology, copper DACs are interchangeable and hot swappable with fiber optic modules.

With a wide range of 40/100G solutions available on the market, direct attach cable becomes the preferable one for 40G/100G applications, since it takes the advantages of cost and power saving, enough data rate for various applications and excellent interchangeability. With the increasing demand for higher bandwidth, direct attach cables are continuing evolving. Fiberstore, as a professional manufacturer and supplier of optical equipment, has various direct attach cables in stock, such as 10G SFP+ DACs, 40G QSFP+ DACs, and 100G QSFP28 DACs. If you want to upgrade your network to 40/100G with direct attach cables, please visit FS.COM.


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