A Direct Attach Copper cable or a DAC cable is a twinax copper cable with factory terminated transmission modules that enable it to connect directly into the ports (or line cards) within active equipment, such as switches, routers, servers or data storage devices, in a data network.
The transmission modules cannot be removed from the cable and so all DAC cables are a fixed length. This is one of the drawbacks of using DAC cables compared to using a combination of fibre cables and optical transceivers.
There are different types of high speed DAC cables; direct and breakout, passive and active. A direct connect DAC cable will connect one port/line card to another. A breakout DAC cable will allow one port to be connected to up to 4 other ports. An active DAC cable will offer slightly longer transmission distance than a passive DAC cable as it uses electronics within the modules at each end to boost the signals.
DAC cables are becoming increasingly popular, not just within data centers but within wider areas of the industry, as they offer a very cost effective, efficient and easy way of making these connections. To further understand their advantages, let’s talk more in detail about what Direct Attach Copper (DAC) cables are and how they are used.
Probably the most popular use of DAC cables is to connect equipment located within the same data rack where transmission distances are from 1 to 3m. As the ratio of 10G ports to 40G ports in a network decreases and more 100G ports are adopted the use of in-rack connectivity is increasing.
An SFP+ to SFP+ DAC cable will plug directly into both pieces of equipment and instantly enable a 10G Ethernet connection.
DAC cables can be used to directly connect a 40G port to another 40G port, but they can also be used to connect one 40G port to up to four 10G Ethernet ports.
DAC cables can be used to connect one 100G port to up to four 25G Ethernet ports. The main constraint is the distance between the four SFP+ ports.
As mentioned above, DAC cables are used for directly connecting ports between active equipment; switches, routers, servers and storage. Their main restriction is transmission distance. Their main benefit is cost, although there are other benefits.
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They can only be used where the physical distance between these ports is small – less than 15m. However, the maximum distance a signal can be transmitted via a DAC cable changes depending on the data rate. As data rates get higher, from 10G to 40G and then to 100G the distance gets smaller and smaller. A 100G DAC can only transmit up to 5m.
These distance limitations mean that the most common use of DAC cables is connecting equipment located within the same data rack, for example, connecting servers to a top of rack switch.
Using a DAC cable will always be more cost effective than using two optical transceivers and a fibre cable. Again the cost savings will depend on the data rate being transmitted, but it is not unusual for them to be 2 or 3 times cheaper. Where their use is permitted by distance, deploying large amounts of DAC cables can lead to a considerable cost saving.
DAC cables are extremely dependable. The modules that plug directly into the equipment ports make a physical electrical contact which ensures a solid connection. The cables are made from 26 to 28 AWG twinax copper and so are physically strong and so are unlikely to be damaged by handling. Both these factors means that it possible for connections to be made swiftly, reliably and affordably in all kinds of applications.
If the transmission distance of DAC cables is not suitable for your application, you may consider using AOC cables. Read more about DAC vs AOC cables.
We understand the importance of having a supply partner you can trust to deliver a quality, high performance solution to connect your network. All our MTP cables and components come with a no nonsense 25 year individual product warranty for complete assurance.
Every switch, router, server manufacturer provides a selection of DAC cables to connect their equipment. However, it is often easier, quicker and cheaper to source DAC cables from other sources.
Using a compatible cable from a reliable and trusted source will not affect any warranties or performance of the switch/server/router that it is plugged into. The only consideration is that the DAC cable needs to have been pre-programmed to match the coding of the host equipment.
If you need to connect a Cisco switch to a Dell server, you cannot use a Cisco DAC or a DELL DAC as neither of these cables will be accepted at both ends.
You can buy a mixed compatibility DAC cable programmed for Cisco at one end and Dell at the other. These are only available through companies like Complete Connect.
DAC cables are completely molded. including all modules and the breakout unit
DAC cables are also available for data rates above 100G. With maximum transmission of only 3m these higher data rate cables offer a range of direct connect and breakout options.
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