DAC Cable: Understanding Direct Attach Copper Cables

A Direct Attach Copper link or a DAC cable is a Twinax copper cable that firmly links the ports (or line cards) inside dynamic hardware, such as switches, network equipment, servers, or any other devices that store or connect information.

DAC cables have been steadily gaining recognition in the industry, inside server farms as well as other extended areas of business. They offer a financially savvy, proficient, and simple method for linking switches and network equipment instead of fiber optic cables.

What Is a DAC Cable?

A DAC cable is made from Twinax copper and processed through module-based plants that provide a reliable electrical connection into active equipment. The modules are fixed and cannot be removed from the cable, so all DAC cables come in fixed lengths. This is one disadvantage compared to using a combination of fiber cables and optical transceivers.

Types of DAC Cables

There are various types of high-speed DAC cables:

• Direct and Breakout DAC Cables: A direct-attach DAC cable connects one port or line card to another, while a breakout DAC cable allows one port to connect to up to four different ports.
• Passive and Active DAC Cables: An active DAC cable offers slightly longer transmission distances than a passive DAC cable as it uses electronics within the modules at each end to boost the signals.

Advantages of Using DAC Cables

Transmission Distance

DAC cables are most effective where the physical distance between ports is relatively small—typically under 15 meters. However, the maximum distance a signal can be transmitted via a DAC cable varies depending on the data rate. As data rates increase from 10G to 40G and then to 100G, the transmission distance decreases. For example, a 100G DAC can transmit up to 5 meters.

These distance limitations mean that DAC cables are commonly used for connecting equipment within the same data racks, such as linking servers with top-of-rack switches.

Cost-Effectiveness

Using a DAC cable is consistently more cost-effective than using two optical transceivers and a fiber cable. The cost savings can be significant, sometimes up to two or three times less expensive. Deploying a large number of DAC cables where applicable can lead to substantial cost reductions.

Reliability

DAC cables are highly reliable. The modules connect seamlessly into the equipment ports, ensuring a stable connection. Made from 26 to 28 AWG Twinax copper, these cables are robust and unlikely to be damaged during handling. These factors make DAC cables suitable for connections that need to be established quickly, reliably, and affordably in various applications.

Applications of DAC Cables

Making 10G Ethernet Connections

The most common use of DAC cables is connecting equipment within data racks where transmission distances range from 1 to 2 meters. SFP+ to SFP+ DAC cables can plug directly into two pieces of equipment and instantly enable a 10G Ethernet connection.

Making 40G Ethernet Connections

The ratio of 10G ports to 40G ports in a network is decreasing regularly. DAC cables can be used to connect a 40G port to another 40G port. They can also connect one 40G port to up to four 10G Ethernet ports using DAC breakout cables. The primary consideration here is the distance between the four SFP+ ports.

Making 100G Ethernet Connections

Similarly, DAC cables can connect a 100G Ethernet port to another 100G port. They can also connect one 100G port to up to four 25G Ethernet ports using DAC breakout cables. Again, the main limitation is the distance between the ports.

Conclusion

Direct Attach Copper cables are becoming increasingly popular due to their cost-effectiveness, reliability, and ease of use in short-distance, high-speed networking applications. Whether you're setting up a data center or upgrading your network infrastructure, considering DAC cables could lead to significant savings and performance benefits.

Frequently Asked Questions About DAC Cables

What is the maximum distance for a DAC cable?

The maximum distance varies depending on the data rate. For example, a 10G DAC cable can typically reach up to 15 meters, while a 100G DAC cable is limited to about 5 meters.

What are the differences between active and passive DAC cables?

Active DAC cables contain electronics in the transceivers to boost signal strength, allowing for slightly longer distances and better performance. Passive DAC cables do not have these electronics and are suitable for shorter distances.

Can DAC cables be used instead of fiber optic cables?

Yes, for short-distance connections (usually within the same rack), DAC cables are a cost-effective and efficient alternative to fiber optic cables and optical transceivers.

Are DAC cables compatible with all network equipment?

Most DAC cables are designed to be compatible with a variety of network equipment. However, it's essential to verify compatibility with your specific devices before purchasing.

What is a DAC breakout cable?

A DAC breakout cable allows one high-speed port (like a 40G or 100G port) to connect to multiple lower-speed ports (like 4x10G or 4x25G ports), effectively splitting the signal across multiple connections.