Introduction to Two Common QSFP+ Cable Types for 40G Ethernet

In order to satisfy the increasing demand for greater bandwidth and the growing amount of data transmission In today’s enterprise data center and networking environments, various kinds of high-performance and reliable cables are designed, like QSFP+ cables. QSFP+ cable is a cable capped at either end with the QSFP+ transceiver, offering high-density, low-cost and low-power 40G Ethernet solution commercially available today. This post will introduce two common QSFP+ cable types—QSFP+ direct attach cable (DAC) and QSFP+ active optical cable (AOC) respectively to make you understand QSFP+ cable better.


With more and more fiber cables applied in data center, someone may consider that copper cables have been out of date, but DAC cable is an exception. QSFP+ direct attach cable (DAC), is a copper 40GBase Twinax cable that comes in either active or passive twinax cable assembly and connects directly into QSFP+ modules, which are permanently attached to both ends of the cable. These QSFP+ modules terminated with DAC cable are not real modules, since they are without expensive optical lasers which makes 40G QSFP+ DAC a more cost-effective solution for 40G LAN, and SAN applications than regular optics. Generally, there are two frequently used types of QSFP+ DAC:

  • QSFP+ to QSFP+ DAC—QSFP+ to QSFP+ DAC consists of a cable assembly that connects two QSFP+ transceivers respectively at each end of the cable (shown in the following picture). This kind of QSFP+ DAC cable is suitable for very short distances and offers a very cost-effective way to establish a 40G link between QSFP+ ports of switches within racks and across adjacent racks. Currently, QSFP+ to QSFP+ DAC cable is mainly available in lengths of 1, 3 and 5 meters (passive cables) or in lengths of 7 and 10 meters (active cable).


  • QSFP+ to 4×SFP+ DAC—QSFP+ to 4×SFP DAC or QSFP+ to 4×SFP copper breakout cables are hot-swappable, low-voltage (3.3V) cable assemblies that connect directly into a QSFP+ module at one end and four SFP+ modules at the other end. They use high-performance, integrated duplex serial data links for bidirectional communication. QSFP+ to 4×SFP DAC cables are optimized to fully leverage 40G Ethernet switches and routers. These cables are used for in-rack connections between servers and top-of-rack (ToR) switches. In addition, they provide state-of-the-art performance, helping IT organizations achieve new levels of infrastructure consolidation while expanding application and service capabilities. The image below shows a Cisco QSFP-4SFP10G-CU5M.



QSFP+ AOC is a high-performance and low power integrated cable solution which provides less expensive, reliable transport for aggregated data rates up to 40Gbps. QSFP+ AOC is much thinner and lighter than QSFP+ DAC, making installation easier. It enables efficient system airflow and has no electromagnetic interference (EMI) issues, which is critical in high-density racks. Like QSFP+ DAC, QSFP+ AOC also has two commonly used types:

  • QSFP+ to QSFP+ AOC—QSFP+ to QSFP+ AOC (see in the picture below) is a 40G parallel active optical cable which transmits error-free parallel 4×10G data over multimode fiber ribbon cables. The QSFP+ to QSFP+ AOC cable is permanently attached to the fiber, with no air gaps, providing protection from environmental contaminants and other user disturbances during installation. It is suitable for the infiniband transmission at 4ch SDR, DDR, and QDR.


  • QSFP+ to 4×SFP+ AOC—QSFP+ to 4×SFP+ AOC (shown in the picture below) is a 4×10G parallel active optical cable for storage, data and high-performance computing interconnectivity. It transmits four separate streams of 10G data over ribbon cables in point-to-multipoint configuration. Similar to QSFP+ to 4×DAC, this kind of AOC cable contains a 40G QSFP+ transceiver on one end and four separate 10G SFP+ modules at the other end. It is available for high-density 40G Ethernet, infiniband and other datacom or high-performance computing applications.



With demand for higher speed increasing, there is no doubt that QSFP+ will have a broad prospect. FS.COM, a professional fiber optic transceiver supplier and manufacturer, offers all the QSFP+ transceiver modules that have been mentioned above. Besides, we also provide many compatible brands QSFP+ modules, like Cisco QSFP-40G-CSR4, Arista QFSP-40G-SR4. Each transceivers purchased from FS.COM is with high performance and quality guaranteed. You can find the most appropriate one from here.


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