Facts to Know About Direct Attach Cables
Direct attach cable, short for DAC, is a fixed assembly which is purchased at a given length, with connector modules permanently attached to each end of the cable. Direct attach cables can be used to connect switches to routers or servers. They are becoming increasingly popular in the network industry, widely used in storage area networks, data centers, etc. The main reason for the popularity of DACs in the market is the price difference, compared with the regular optics. To make better use of direct attach cables, here are some facts you may not know but should know about them.
1.DACs, like QSFP+ to QSFP+ cable or SFP+ to SFP+ cable, are more cheaper than the regular optics. Because the "transceivers" on both ends of direct attach cables are not real transceiver modules. DAC is designed to use the same port as an optical transceiver, but compared with reguar optical transceivers, the connector modules attached to the DAC leave out the expensive optical lasers and other electronic components, thus achieving significant cost savings and power savings in short reach applications. Without those expensive optics components, the cost of DACs is much lower. Thus, though using the same port as an optical transceiver, DACs can achieve significant cost savings and power savings in short reach applications.
2.In related articles or product descriptions of some DAC vendors, there is always a point saying that active direct attach cables are lighter and thinner than passive direct attach cables. Actually, it is a wrong point of view. If you have a practical experience of using both active and passive direct attach cables, you may find that there is no big difference between them in weight and appearance.
3.The main difference between active DAC and passive DAC is that there is a driving chip in the design of active DAC. In active direct attach copper cables, there are signal processing electronics in the modules to improve signal quality and provide a longer cable distance. Otherwise, direct attach copper cable is considered passive.
4. AOC (active optical cable) is one form of direct attach cables. An active optical cable integrates optical fiber, "fiber optic transceivers", and control chip. AOCs are with advantages of light weight, high performance, low power consumption, low interconnection loss, EMI immunity and flexibility, etc. They are now considered as the rising star in telecommunications and datacom transceiver markets. The picture below shows a Cisco SFP-10G-AOC10M compatible SFP+ active optical cable.
5. As mentioned above, the thickness and weight do not depend on the active or passive function. In fact, they are divided according to their characteristic of AWG (American Wire Gauge). For instance, AWG24 DAC is thicker and heavier than the AWG30 DAC. Due to different wire diameters, the longer the cable, the more inconvenient AWG24 DAC becomes, compared with AWG30 DAC. Moreover, there is also limited bend radius. Thus, the longer the distance, the higher the AWG rating should be.
6. Whether to choose active DAC or passive DAC, the transmission distance is an important factor that you need to take into consideration. When the transmission distance is over 5 metres, active DAC is more suitable than passive DAC, because it will cause the signal issue when using passive DAC for long-haul transmission.
Fiberstore offers a variety of high speed interconnect DAC assemblies, including 10G SFP+ cables, 40G QSFP+ cables, and 120G CXP cables to satisfy the demands from 10G to 100G interconnection. All of those direct attach cables can meet the ever-growing need to deliver more bandwidth cost-effectively, and can be customized to meet different requirements.
