As the increasing demand for higher bandwidth and reliability, 40G Ethernet comes into being and it gradually becomes ubiquitous in telecommunication networks. Fiber optic transceiver including 40GBase-LR4 QSFP+ and 40GBase-SR4 QSFP+ is the most commonly used method to achieve 40G. The former one is suitable for long distance data transmission, while the latter one is more available for short distance data transmission. When the required distances are short in network interconnections, besides 40GBase-SR4 QSFP+ transceiver, there is another option—40G QSFP+ AOC. Both designed for short-range data communication, what are the differences between these two 40G solutions? The following part will illustrate in details.
40G QSFP+ AOC—40G QSFP+ AOC is a four-channel parallel active optical cable and each channel is capable of transmitting data at a rate of 10Gbps per direction, providing a total rate of 40Gbps. It consists of a cable assembly that connects one QSFP+ module at one end, while the other end is terminated with QSFP+, SFP+, LC or SC. Compared to 40GBase-SR4 optics, 40G QSFP+ AOC removes the need for fiber optic connectors and has the similar performance as the former, which seems to be a much faster and easier methods for 40G interconnection. The following image is a Cisco 1m QSFP+ to QSFP+ AOC.
40GBase-SR4 QSFP+ —40GBase-SR4 QSFP+ primarily enables high-bandwidth 40G optical links over 12-fiber parallel fiber terminated with MPO/MTP connectors, which can support link lengths of 100 meters and 150 meters respectively over laser-optimized OM3 and OM4 multimode fibers. Here is a Cisco 40GBase-SR4 QSFP+ transceiver.
Supporting Link Length—As we have mentioned above, 40Base-SR4 QSFP+ and 40G QSFP+ AOC are both good choices for short distance data transmission. In general, when the transmission distance is less than 100 meters, two methods have the same performance, but when it comes to link lengths over 100 meters, 40GBase-SR4 QSFP+ has more reliable and better performance than 40G QSFP+ AOC.
Installation—It is known that 40G QSFP+ AOC is a cable assembly that is permanently pre-terminated with transceiver modules or fiber optic connectors at both ends in the factory. Users just need to plug the two connectors into the switch. But for 40GBase-SR QSFP+, you need to connect the patch cord attached with connectors to the transceiver first before plugging the modules into the switch. It seems that installing a QSFP+ AOC is much more easier and time-saving than using a QSFP+ module.
Working Stability—For regular use and maintenance, it is inevitable to plug out cables and connectors out of switches or servers in data center. With the repeating plugging, the reliability and stability of a component become extremely important. We have mentioned that 40G QSFP+ AOC is factory pre-terminated with connectors, while the 40GBase-SR4 QSFP+ needs additional connectors and fiber cables to achieve connection. Thus, compared to 40GBase-SR4 QSFP+, the stability of 40G QSFP+ AOC will be less affected by the repeating plugging of daily use.
Cost—Choosing a solution for 40G interconnection, two aspects of cost should be taken into consideration: one is material cost, and the other is maintenance cost. Actually, a 40G QSFP+ AOC is more expensive than a 40GBase-SR4 QSFP+ transceiver, although a 40GBase-SR4 QSFP+ may need additional fiber patch cables to achieve connection. However, in nowadays data center, the value of maintenance cost is much more important than material cost. With 40G QSFP+ AOC, data center managers will be free from cleaning the optical connectors as well as from termination plug and test when troubleshooting, which is time-saving and cost-efficient.
With the existence of popular optical transceivers, it is a surprise to find a new solution—40G QSFP+ AOC for short distance 40G interconnection. Compared to 40GBase-SR4 QSFP+ transceiver modules, 40G QSFP+ AOC provide more reliable and stable working condition, and easier installation, as well as lower cost, especially in maintenance cost. But for the long-distance data transmission performance, 40GBase-SR4 QSFP+ transceiver can do better. Through this passage, hope you can choose the right 40GbE short reach solution for your references.
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