Factors Have Influence on DAC Cable Performance
High Speed direct attach cable (DAC cable ) is a type of factory terminated cable assemblies for active network equipment point to point connection in data center, storage area network and high performance computing center to meet high bandwidth, connection density and low latency requirement. The DAC cables has passive and active types both constructed with shielded twin axial cooper cable in varying gauges from 24 to 30AWG. As basic high speed cable, it has many advantages to replace the fiber transceivers at lower cost.
The Advantage of DAC cables
1. Compared with the active optic cable, the passive DAC cable length limit is 5m, while the Active DAC length is 15m, it is more suitable for short transmission. it has strong exchange capability in integrated solution.
2. The DAC cable use copper cable which has features such as good heat dissipation, energy saving, large communication capacity, high transmission stability, good confidentiality etc.
3. Low power consumption. Particularly with passive DAC cables since they are self contained components and not bound by transmission specifications as transceivers, short transmission distance maximum 15m to reduce the signal power and internal circuitry. The passive DAC only consume a very small amount of power around 0.15W, while the active DAC power consumption is around 0.5-1.0W
4. Low price, direct attach cables are less costly than using discreet transceiver with field connected structure cabling duo to simplified interconnection to low down the whole datacenter cabling cost
The factors to have influence on the DAC cable performance
Based on the material and structure, here may find the factors to degrade the cable performance.
1. A bent cable will weaken the transmitted signal. The cables are in the form of a single cable which is easy to bend, and the recovery ability after bending is relatively poor. Therefore, in the process of termination and usage, it is necessary to avoid twisting and bending of the insulated core wire as much as possible to affect the performance.
2. The insulating part of the wire is a foamed structure, which has poor mechanical properties. It is easy to be squeezed or stretched to be deformed result in foam layer structure destroy. Therefore, during the processing and use of the wire, try to avoid the insulation core wire from being squeezed or stretched
3. The pair of wires in the cable is a parallel wrapping structure without twisting pitch, so it is easy to bend and deform. Therefore, when processing and using the wire, try not to bend the wrapped wire pair to ensure the smallest possible damage to the wrapped structure.
4. In order to have good electrical performance, a relatively large cable pitch can ensure the best electrical performance, but at the same time, it also degrades bending performance. Therefore, in the process of wire processing and use, 20 times or more than the OD of the wire as bend radius is recommended, the bend radius of the DAC cable is from 23mm, 25mm, 33mm, and 38mm for different type AWG cable.
5. When welding foamed insulation wires, tin dipping and welding time must be reduced as much as possible, which can reduce insulation shrinkage and melting and reduce the impact on high-speed cable performance.
Based on the technical characteristics and its weight, the top of rack and adjacent racks use the DAC cables is recommended to have the low-cost operation.