DAC vs. AOC

DAC vs. AOC: Choose the Right Cabling by Application

The rapid growth of various online applications, cloud-based services and virtualization solutions continues to drive demand for high-speed switching. To meet these demands, data center operators are increasingly deploying top-of-rack (ToR) switches as leaf switches in the spine-leaf architecture. This network design lays the foundation for modern data center applications while paving the way for future growth.

ToR is the most widely used architecture today when it comes to cabling between racks in large networks such as data centers. In doing so, today's networks must have higher-performance cabling and cost-effective connections

Choosing the right cabling

Direct Attach Copper (DAC) and Active Optical Cables (AOC) are the two main cabling solutions for data center and enterprise network connections. Both AOCs and DACs are plug-and-play solutions that allow users to optimize the existing network without new fiber cabling.

Direct Attach Copper (DAC)

DAC stands for Direct Attach Copper, which is an high-speed twinax cable. It is a copper cable with a (Q)SFP module on both ends that plugs into a fiber port. DAC cables can be divided into passive DACs and active DACs. Passive DACs do not affect the signal because there are no electrical components. The maximum range of a passive DAC is 7 meters. Active DACs have a more powerful chip for signal processing. This increases the range to around 10 meters.

The main application of DACs is to connect servers to switches inside or adjacent to the rack. In other words, these direct-connect cables can be used as an alternative for ToR connections between ToR switch and server or for stacking switches.

Active Optical Cable (AOC)

An Active Optical Cable (AOC) is the optical alternative to the copper-based direct connection cable. AOCs are used in high-speed transmission technology and are optical direct connection cables consisting of multimode optical fibers. These are available only as active optical cables to perform optoelectronic conversion. As a result, ranges of up to 100 meters can be achieved.

AOCs are often used at multiple locations in the data center to achieve a large number of cable connections of multiple server racks. In addition, AOCs in the data center can also be implemented in multiple main network areas such as spine, leaf or core switching areas.  

Practice Advice

In practice, DAC cables and individual transceiver modules with fiber optic cables have proven themselves over AOC cables. Especially for short cabling distances within a server rack, DAC cables have their strengths. They also score high in energy consumption and ease of handling.

Although AOC cables are less expensive than individual transceiver modules. Transceiver modules are the better choice, especially for longer distances of 10 meters or more, due to their greater flexibility. Longer cables are usually laid in data centers via cable trays. In the course of a later expansion or modernization of the network, transceiver modules can be easily replaced, as the existing cabling can continue to be used. AOC cables, on the other hand, have to be re-routed as part of the modernization and lead to increased additional expenses.

Summary

Whether you need access-layer connectivity or need to scale your data center network with a spine-leaf architecture to grow your business, both DAC and AOC are available in QSFP form factor. However, in real-world testing, AOC cables can't compete with traditional transceiver modules and fiber-optic cables. DAC, on the other hand, beats both variants when cabling inside a server rack and are the winner in the practical test.

Pan Dacom Direkt not only offers 1G to 400G transceivers in all common form factors, including patch cables, but also DAC and breakout DAC cables for optimal network design. Download now your 100G, 200G and 400G DAC cable price sheet or contact your account manager right away to find the best cabling solution for your data center.