A direct attach cable, short for DAC cable, is a type of factory terminated twinax cable used to connect switches to routers or servers. A high speed direct attach cable is a type of factory terminated cable assembly used in data centers for point-to-point connections of active network equipment. These cable assemblies consist of fixed lengths of shielded copper coaxial or fiber optic cable with pluggable transceivers factory terminated on either end. Direct attach cables are available in popular transceiver form factors, including SFP, SFP+ and QSFP . These cables consist of fixed lengths of shielded copper coaxial or fiber optic cable with fixed pluggable transceivers on either end with varying gauges from 24 to 30AWG. DAC cable can achieve interconnection up to 15m via twinaxial copper cable, and reach 100m over active optical cable at 10Gbps, 40Gbps or beyond.
As the development of fiber technology, someone may deem that copper technology is out of fashion. This is not true for direct attach copper cable. In fact, direct attach copper cable still has its advantages in the market.
Types of DAC Cable
Generally, according to the construction difference, the DAC cables can be classified into two types: passive DAC cable and active DAC cable.
Passive DAC cables have no electrical components built into the cable assembly. Hence, it has the minimal power consumption of no more than 0.15w and generally for short reach up to 7m.
Active DAC cables have signal amplification and equalization built into the cable assembly. Therefore, it allows a little longer transmission distance up to 15m and ensures better transmission quality. whereas it has a higher price and consumes more power around 0.5-1w.
Advantages of DAC Cable:
Higher data transmission rate: The DAC cable can support data transmission rates from 4Gbps to 10Gbps, which is higher than traditional copper cable.
Strong interchangeability: With the development of copper technology, DAC cable and optical transceiver are interchangeable and hot swappable.
Low cost: Copper cable is cheaper than fiber, and using DAC cable will reduce wiring cos.
Good heat dissipation: The DAC cable is made of copper core and has good heat dissipation effect.
Factory Terminated Performance – DACs and AOCs are terminated and 100% tested at the factory. This provides consistent and expected transmission performance levels for the channel.
Disadvantages of DAC Cable:
Reduced Cable Flexibility – Passive and active copper DACs have a larger bend radius and weight than traditional structured cabling or AOCs, which can sometimes place additional demands on the cable management and airflow management within a rack or cabinet.
Reduced Modularity – Structured cabling provides improved modularity through the use of patch panels and other components to make moves, adds and changes quicker and easier. DACs and AOCs are point-to-point cabling that require some additional labor since they need to be completely pulled out of racks, cable managers, cable tray, and other infrastructure elements.
Limited Distance – Transceivers and structured cabling are designed to work together in a universal and cohesive system. Therefore, pluggable transceivers are required to reach 100m or beyond, while DACs and AOCs are not.
Applications for Direct Attach Cables
Direct attach cables can be used in a variety of applications and locations in a data center. In general, this pre-terminated solution is particularly effective for the following applications:
Top of Rack/Adjacent Rack – Passive or active DACs are ideal for shorter ToR or rack-to-rack runs with cost-conscious budgets.
Middle of Row – Active DACs may be a perfect solution in this application, as long as the runs are less than 15m.
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