Category Archives: Direct Attach Cable


40GBASE-SR4 QSFP+ transceivers is now being widely used for 40G network interconnection in short distance. This is a highly integrated component which has small size and uses four channels to support conversions between optical signals and electrical signals over a high data rate up to 40G. However, another component which can replace this transceiver in network interconnection becomes popular in data center application. It is 40GBASE QSFP+ AOC (active optical cable).

AOC is a kind of direct attached cable (DAC), which is available in 10G, 40G and even 120G. 40GBASE QSFP+ AOC contains a QSFP+ connector on one end and one QSFP+ connector on the other end which are linked by a length of fiber optic cable. There are also fanout versions of 40GBASE QSFP+ AOC with one end connected with a QSFP+ connector and the other end with several SFP+/XFP connectors. It looks like a fiber optic patch cable, but, it has a similar function of optical transceiver, and also can transmission signals with its fiber optic cable. 40G AOC removes the process of two modules, which must be done in a 40G interconnection using 40G SR4 QSFP+ transceiver. It seems that both 40G AOC and 40G transceiver are good solutions for interconnection. However, everything has it’s Pros and Cons. Figure out the one that fits your application is the most reasonable way. The following is to offer comparison between these two components for your references.


Transmission Distance: The first aspect to be considered is the transmission distance of these two components. Currently the 40G transmission is usually used in backbone network. Thus, to assure the transmission quality, distance should be ensured. Both 40GBASE-SR4 QSFP+ and 40GBASE QSFP+ AOC are designed for 40G transmission in short distance. Generally, when the distance is shorter than 100 meters, the two have similar performance. However, when it’s longer than 100 meters, AOC cannot perform as good as transceiver. Currently most 40G AOC provided by the manufacturers are less than 100 meters. However, Fiberstore can provide 40G AOC up to 300 meters.

Reliability: In work state, both of the components should be inserted into a switch or server. And the repeating plug of them are necessary for daily use and maintenance. It is known to us that, these actions might affect the performances of the component. Thus reliability of these components should be considered. The connectors of 40G AOC are factory pre-terminated, while QSFP+ SR4 transceivers are connected by additional MPO connectors and fiber optic cable. Thus, compared with QSFP+ SR4 transceiver, AOC is less affected by the repeating plug during daily use. It has been proved that AOC has better reliability than that of transceivers.

Installation and Maintenance: it has been clear that 40G AOC is much easier during installation, as the connectors have already terminated in factory. Customers just need to plug the two connectors in the switches, then can start working. While, for 40G SR4 QSFP+, additional patch cords with MPO connectors are used to finish the link. If there is a fault in the interconnection, for AOC, you can just replace it with another AOC. However, for interconnection using 40G QSFP+ SR4 transceivers, you have to locate the fault firstly by testing the patch cords and optics.

40GBASE-SR4 QSFP+ transceiver under test

Digital Diagnostic Monitoring (DDM): to achieve the best working state, most modern transceivers are armed with DDM function. With it, the working states and performance of the optics can be visually controlled. No wonder that 40GBASE-SR4 QSFP+ has such function. However, 40G AOCs that are provided by the market now do not have it.

Cost: two main aspects should be considered in selection a product in data center. One is the material cost. The other is the maintenance cost in the daily use. AOC has advantages over transceivers on both aspects. The price for 40G AOC is generally cheaper than 40G QSFP+ SR4. In addition, the interconnections reply on 40G transceivers also need additional fiber optic cables. The latter aspect has been clearly illustrated in the above. AOC can save more in general.

In conclusion, 40GBASE-SR4 QSFP+ can achieve best working status by using DDM and it has better performance when the transmission distance is longer than 100 meters. While 40GBASE QSFP+ AOC is cheaper, easy to manage and test, and it has similar performance as the former does over transmission distance less than 100 meters. For your reference, Fiberstore offer a wide range of both 40GBASE-SR4 QSFP+ and 40GBASE QSFP+ AOC. You can trust all of them cause they are all be tested before they go to the marker. Kindly contact or visit FS.COM for more detail, if you are interested.

Fanout Assemblies in 40G Interconnection

40G transmission is very common in the backbone network now. However, not all the devices and network are upgraded to 40G. To adapting the network between devices and network of different data rate. It is necessary to connection 40G devices to 10G devices for network interconnection. To solve this problem, fanout technology is be accepted and widely used in data center. Fanout products for interconnection is easy to understand. It’s kind of like the water pipeline in our building: water is transferred from the trunk pipeline in a building. Then trunk pipeline fans out into several pipelines that have smaller diameters to bring the water to every house. This post will introduce several Fanout products that are commonly used for 40G data center interconnection.

40G MPO Fanout Cables

The first fanout component is 40G MPO fanout cable, also called breakout cable or harness cable. MPO fanout cable is a multi-fiber optical cable with one end terminated with a male/female MPO connector and the other end attached with several LC connectors. Actually, there are various types of MPO fanout cables, according to connector type, cable length and cable type. But they all have the similar structure. Here will introduce three most popular MPO fanout cables according to the package type.

MPO-8LC fanout cable

The first one to be introduced is also what most customer need. This cable is fan out into 12 fibers or 24 fibers. The above picture shows a typical 12-fiber MPO harness cable. The MPO connector of this fanout cable is linked to 6 duplex LC connectors, which is really useful for backbone cabling from 40G devices to 10G devices.
The second one is a little bit smaller version of the former. The fibers are fanout directly from the MPO connectors. With small size, this kind of mini MPO harness cable can be easily put into patch panel and increase the cabling density largely and effectively.

12-fiber MPO cassette

The third to be introduced is a special one—MPO cassette. Literally, it looks like a cassette and looks very different from other MPO fanout cables. However, when you look inside the cassette, it has not much difference from other MPO fanout cables. MPO Cassette actually contains one or several mini MPO fanout cables in side the cassette, which is designed for those who want have everything in clean and tidy status. As it can be installed in a standard rack and the cables are all well protected. A 12-fiber MPO cassette usually has a 12-fiber mini MPO fanout cable in side the cassette, with a MPO connector on the backside and 12 LC connector in the front. For a 24-fiber MPO cassette, there could be a 24-fiber fanout cable or two 12-fiber cables inside. The following picture is a MPO cassette with two 12-fiber MPO fanout cable inside it, thus there are two MPO connector on its backside.

24-fiber MPO cassette with two 12-fiber MPO fanout inside

40G Fanout Direct Attach Cables

To decrease the 40G interconnection cost, Direct attach cable (DAC) is being widely used. There are also fanout versions of 40G DAC which support 40G to 10G cabling. These kind of 40G DAC usually have one QSFP+ connector on one end and four SFP+/XFP connectors or several LC connectors at the other end. For example, the following is 40G QSFP+ to 8 LC DAC. The QSFP+ connector of it can be used to plug in the 40G device which has QSFP+ port. On the other end, the four duplex LC connectors are used to separately connect four SFP+ transceivers , which are used to plug in 10G devices with SFP+ switched (shown in the following picture). If you used a 40G QSFP+ to 4 SFP+ DAC, this process would be easier, cause the SFP+ connector can be plugged into the SFP+ switch directly.

QSFP-8LC AOC for 40G to 10G cabling


All in all, fanout technology plays an important role in the 40G data center for both connecting devices supporting different data rate and distribution. Most fanout products are factory pre-terminated. The installation and maintenance doesn’t need many skills. In Fiberstore, a variety of fanout products of high quality and reliability can be customized according to your application. If you are seeking for solutions for fanout product, please feel free to contact for more details.