What is a Direct Attach Cable (DAC) ?

Introduction to Direct Attach Cable (DAC)

Direct Attach Cable is a category of interconnect used in telecommunication networks and data centers such as Active Optical Cable (AOC) and Optical Transceiver.

40G QSFP+ to 40G QSFP+ Direct Attach Cable

40G QSFP+ to 40G QSFP+ Direct Attach Cable

What is a Direct Attach Cable ?

A DAC is two transceivers attached together by a copper cable, creating a one part assembly. Like, AOC, Direct Attach Cable can not be separated.

Direct Attach Cables can reach distances from 0.5 meters up to 10 meters, but they are commonly used for distance under 5 meters. The DAC technology has been developed for several data rate from 10G SFP+ to 400G QSFP-DD.

DAC also exist as breakout cables, where one side on the assembly is divided in four cables, each terminated by a transceiver of a smaller data rate, allowing to connect a larger number of ports and devices. (See below photo for example)

100G QSFP28 to 4 x 25G SFP28 Direct Attach Cable

100G QSFP28 to 4 x 25G SFP28 Direct Attach Cable

The difference between Passive DAC and Active DAC

There are two types of DAC, the passive copper cable that can reach distances from 0.5 to 5 meters and active copper cable that can reach distances up 10 meters. Passive DACs have no electrical components and thus consume no power. However active DAC contain electrical components to boost the signal, allowing to ensure its quality through longer distance. Of course, the addition of the electrical components make the active DAC slightly more expansive.

What are the advantages of DAC ?

Compare to Active Optical Cable

Direct Attached Cables are a very common method used for very short-range distances because of the their low-cost. Indeed, they are the cheapest solution to connect network equipment, because of the hardware price and they low power consumption. However, unlike AOCs, DACs are heavier and vulnerable to the effects of electromagnetic interference (EMI).

Compare to  using transceivers and separated cables

Direct Attach Cables are more suitable for short distance connection because they are considerably cheaper than using transceivers and separated cables. In addition, there is less maintenance work because there is no need of assembling and cleaning the connectors.

How the Direct Attach Cables are used?

Direct Attach Cables are the perfect cost effective solution to connect devices seperated by small distances. DAC are mostly used to connect switches, servers and storage inside the same rack or an adjacent rack of a data center for example. For distance above 5 meters it is recommended to use Active DAC to keep the strength and quality of the signal. For distance above 10 meters, the use of Active Optical Cables is preferred.

Direct Attach Cables Products

10G SFP+ DAC 10G SFP+ to SFP+ DAC OPSFPP-T-xx-P xx= 0,5 to 7 meters
40G QSFP+ DAC 40G QSFP+ to QSFP+ DAC OPQSFP-T-xx-P xx= 0,5 to 7 meters
40G QSFP+ to 4 SFP+ DAC OPQSFP-T-xx-P/SFPP/4 xx= 0,5 to 7 meters
25G SFP28 DAC 25G SFP28 to SFP28 DAC OPSF28-T-X5-PE xx= 0,5 to 5 meters
100G QSFP28 DAC 100G QSFP28 to QSFP28 DAC OPQS28-T-XX-PE  xx= 0,5 to 5 meters
100G QSFP28 to 4 SFP28 DAC OPQS28-T-XX-P/SF28/4 xx= 0,5 to 5 meters
400G QSFP-DD DAC 400G QSFP-DD to QSFP-DD DAC  OPQSDD-T-XX-PEL xx= 0,5 to 3 meters

For DAC products, the length and the gauge size can be customized upon request.

About Optech

Optech Technology Co. Ltd was founded in 2001 in Taipei, Taiwan. The company was created with a sole purpose, to provide a wide and high quality portfolio of optical products to a very demanding and fast evolving market.

To respond to the permanent increase of IP traffic, Optech portfolio is constantly growing. Since the beginning, the company has always been up to date with the latest innovations on the market. Today, we are proud to deliver a large selection of 25G SFP28, 40G QSFP+, 100G QSFP28 and 400G QSFP-DD optical transceivers and cables.

Optech has a large portfolio of products which include optical transceiversdirect attach cablesactive optical cablesloopback transceiversmedia converters and fiber patch cords.

Through its large selection of optical products, that have a range of data speed from 155 Mbps to 400 Gbps and reach distances up to 120km, Optech products are suitable for various industries such as telecom, data centers as well as public and private networks.

For more information you can visit www.optech.com.tw or contact us at sales@optech.com.tw.

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