In today’s data center, direct attached cable (DAC) is widely used for interconnection. With 40G migration, DAC becomes more popular, because they can support the high data rate and complete the interconnection in short time effectively. Currently, there are three types of DACs: passive copper cable, active copper cable and active optical cable (AOC). However, different DAC have different performances and prices. Passive or active? Copper or optical? Which DAC is the one you need?
In data center, the battle between performance, transmission distance and cost has never ended. This is also true to the selection of DAC for 40G data center interconnection. To find a cost-effective 40G DAC solution for data center interconnection with reliability and stability, this article will provide you the solution by several rounds of battle between the three types of DAC.
The first round of battle is transmission distance which is always the first factors to be considered during the selection of DAC. This is because it is closely related to the transmission distance. There is no wonder that optical cable can transmit signals over longer distance than that of the copper cable. When the data rate required for interconnection is less than 5 Gbps, the passive copper cable is usually used for interconnection in data center. However, they can only support 40G transmission over really short distance. Optical cable is used to overcome the challenge of the distance. Supported with connectors that are embedded with electronics/optics, 40G active optical cable can support 40G transmission up to 100 meters. Active copper cable can support 40G transmission over copper cable up to 15 meters with QSFP+ connector embedded with electronics. In the battle over transmission distance, optical active cable wins without doubt.
The connectors attached with AOC and active copper cable are the main reason why the two cables can support 40G transmission over longer distance than that of passive copper cable. AOC which can support the longest 40G transmission distance is with the highest power consumption—more than 2W. The power consumption for active copper cable is only 440mW. However, passive copper cable requires no power during the transmission. In this battle, passive copper cable wins and AOC lost its advantages and is in the third place.
Cooling is closely related to data center reliability and life of use. The DAC in the data center can also affect the cooling of data center. The cable size and power consumption will directly influence the cooling efficiency of the data center. The thinner the cable is, the better dispersion devices in data center would have. Among the three types of DACs, optical cable is the thinnest among the three types of DAC. Active copper is also thinner than passive cooper cable. Active copper is also thinner than passive cooper cable. As mentioned, AOC has the highest power consumption and active copper cable has a lower power consumption, while passive copper cable requires no power. In this round of battle, it’s hard to tell which one wins. It depends on the practical and specific situations in the data center.
It is clear that copper is much cheaper than optical cable. AOC, with connectors embedded with electronics and/or optics is the most expensive one. AOC is strongly recommended if cost is not a problem. It has the best transmission performance. However, for many data centers, it’s hard to have an ideal situation like this. Cost sometime can determine the final decision of the choice in data center cabling. Most of the components in data center are expensive and require careful maintenance. Passive copper cable is much cheaper than AOC. However, it cannot support 40G transmission in most cases in data center. Active copper cable is less expensive than AOC and can support longer transmission than passive copper cable seems to be a good choice.
After several rounds of battle, the price and performances of the three DACs are clear. What to be considered next is the practical application. After several rounds of battle, the price and performances of the three DACs are clear. What to be considered next is the practical application. In most data center, most server to server connections require 2-5 meters, while rack to rack connections are required to be connected by 8-12 meters cables. For 40G transmission, the application of passive copper cable is limited because it only supports really short transmission distance. AOC has the best transmission performance. However, it costs most in both material and daily use. It’s expensive and needs more power. And in daily maintenance, they need careful management, because the optical cables are fragile. If cost is not a problem, then AOC is suggested for 40G transmission.
What to be considered next is the practical application. In most data center, most server to server connections require 2-5 meters, while rack to rack connections are required to be connected by 8-12 meters cables. Due to the Active copper cable, which is less expensive and can support 40G transmission up to 15 meters with low power consumption, can satisfy the regular interconnection requirement for distance and cooling in most data center. For the cost, you also don’t need to worry about, as it is much cheaper than AOC and it is stronger than AOC during cabling and daily maintenance. If you are looking for an economical solution to upgrade your data center to 40G, then active copper cable won’t let you down. The following chart can illustrate the advantages of active copper cable clearly.
|DAC Type||40G Transmission Distance||Power Consumption||Price|
|Passive Copper Cable||5m Reach||0W||Inexpensive|
|Active Copper Cable||15m Reach||440mW||Moderately Priced|
|Active Optical Cable||100M+ Reach||2W+||Expensive|
Fiberstore provides a full range of 40G active copper cables of high quality. All the connectors and cable lengths can be customized according to your applications. You contact email@example.com for more details.