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All About QSFP Cables, Connectors, and More
Amphenol is your industry leader when it comes to the innovation, design, manufacture, and supply of high-performance cable connectors and assemblies. Our customer base consists of all major data center, networking, HPC, telecom, server and storage system providers across the globe. Whether you have compliance restraints or strict design specifications, our team is here to help design, develop, and test cabling systems for your equipment, infrastructure, and network. Amphenol provides customers with products that enable performance at the leading edge of next-generation, high-speed technology.
QSFP Connectors and Cable Assemblies
The acronym QSFP stands for Quad Small Formfactor Pluggable, and QSFP is a family of connectors and cable assemblies that share a mating interface. A mating interface is where the two separable pieces of a connector system that come together to form an interconnect. QSFP’s mating interface is a card edge defined in a multi-source agreement called INF-8438i. A card edge mating interface is the end of a printed circuit board with exposed and plated pads. These pads make contact with the beams of a mating QSFP connector. The card edge layout is shown below.
The QSFP connector is quite small: 12.5mm x 18.2mm x 5.6mm. However, the connector is not used by itself. A press-fit cage is assembled over the connector to guide and latch the QSFP cable assembly. For some QSFP arrays, the cage is integrated with the connector so both can be placed on the PCB simultaneously.
The cable is unlatched by pulling the pull-tab. The pull-tab is shown below in green. However, the shape, size, and color of the pull-tab is customizable. Occasionally, we’ll even put a custom emboss on the die-cast backshell with the customer name and logo. This allows the customer to sell the product as their own.
QSFP cable assemblies are used in networking devices such as patch panels, switches, and host card adaptors (HCA) and compute devices such as servers. The host card adaptor is connected to a computer via a PCIe slot. Since the data needs to pass through the PCIe slot, the maximum throughput can be limited to the PCIe protocol implemented on the HCA.
QSFP connectors and cable assemblies have many options/configurations, and performance levels. The table below summarizes these performance levels.
Any QSFP cable assemblies can be plugged into any QSFP or QSFP DD connector. However, QSFP DD cable assemblies can only be used with QSFP DD connectors.
The cages have many options. A QSFP connector cage could house 1 to 6 connectors. The connector configuration could be one row and up to six columns or two rows up to three columns. In this way you can configure a 36-port switch in multiple ways. For example, you could use six 1x6 connector and cage arrays in a belly-to-belly configuration, or you could use six 2x3 connector and cage arrays that are all mounted on the same layer.
Optional heatsinks and light-pipes are available. These get assembled with the cage to move heat away from the QSFP module or to get access to network activity, respectively. The heatsinks come in fin and pin styles and have three available heights: 4.2mm, 6.5mm, and 13.5mm. Similarly, the light-pipes come in two options: 1.4mm diameter or 2.6mm square.
QSFP interconnects include direct attach copper (DAC), active optical cables (AOC), optical modules, and active copper cables (ACC). DACs are the least expensive option. They provide connectivity that relies on signal conditioning from the host. The maximum length achievable depends on the insertion loss of the cable assembly, which is driven by the IEEE specifications (see below) and the cable assembly insertion loss is determined by its length and cable gauge (AWG). The size of the wire is inversely proportional to its AWG. The table below shows AWG vs wire diameter for QSFP cable assemblies. As you can see from the table, Amphenol’s QSFP cable can be as small as 34AWG and as large as 24AWG. There are mechanical limitations that make going to 24AWG impossible for some QSFP applications. Each QSFP cable assembly datasheet will provide these limits.
QSFP Active Optical Cables
AOCs are cable assemblies that use permanently attached optical fibers instead of copper cables. The AOC modules contain transimpedance amplifiers, VCSELs, and lenses to change the electrical signals from the host to light. The light is converted back to electrical signals on the receive side before leaving the module. The process requires power from the host, and the modules are not 100% efficient. Therefore, power loss from heat is removed from the cable assemblies with the module heatsinks and fans. In AOC ports, the host’s signal conditioning capability only needs to compensate for the host board loss instead of the entire cable assembly. Amphenol’s AOCs are built with single process flow, which includes a common laser termination, that allows the same core equipment to be used across a wide range of products. These products share many components, and do not use flex circuits in any of their optical engines. The result is a small tolerance loop between the optical devices and lenses which leads to very high yields.
QSFP Optical Transceivers
Optical transceivers are small powerful devices that connect a switch or other networking device to a copper or fiber optic cable and are commonly used to add fiber ports. When used in conjunction with fiber optics, data is transmitted via an optical fiber in the form of light pulses, traveling at very high speeds and can cross extremely long distances. In the fiber optic network, the transceiver is a very important component because it is a laser that is wavelength specific and converts the electrical signals to optical signals. The transceiver then transmits the data over the optical fiber where it is transformed into a signal that has a unique wavelength. Signals that are 850nm, 1310nm and 1550 nm are known as wideband. Signals that are CWDM or DWDM are known as narrow bands. Because of the unique property of light, each channel is not able to interact with each other. This means that a mix of wideband and narrow band can be transported over a network.
Optical modules are similar to AOCs, because they convert the electrical signal to light and back to electric. However, the optical fiber is separable, and accepts either an MPO-12 cable or LC cable. MPO-12 is typically multimode fiber (MMF), and LC cable is typically single-mode fiber (SMF). Both MPO and LC wires are considerably smaller than copper cables.
QSFP is a compact, hot pluggable network interface transceiver that is commonly used for data communications. QSFP can carry 4 channels at the same time, with each channel able to handle 1 GB/s data. The QSFP+ is an upgraded version of the QSFP, and can support 4 x 10 Gb/s, which can be combined into a 40 Gb ethernet link. QSFP+ can replace 4 SFP+ transceivers, which allows for greater port density and an overall system cost saving.
QSFP28 is a QSFP module that is designed for 100G applications and offers four channels with data rates ranging from 25Gb/s up to 40Gb/s.
The type of transceiver used depends on the cable type, application, required optical range of network and desired data transmission rate.
QSFP Active Copper Cable Assemblies
The last type of QSFP is an ACC (Active Copper Cable) Assembly. ACCs have integrated signal conditioning and amplifiers to overcome copper cable losses. That means they can be considerably longer than DACs of the same AWG. For similar lengths, ACCs use smaller AWG than DACs which can improve airflow. Also, the host treats ACCs the same as an AOC, and the host only needs to compensate for the losses from the IC to the module. They typically draw less power from the host and are less expensive than AOCs, but cannot be as long.
Although QSFP cable assemblies are guided by specific standards and MSA’s, Amphenol provides leading edge market timing when it comes to 200G, 400G and now 800G QSFP-compatible solutions. Production plans are in place for 800G OSFP and QSFP DD cable assemblies, giving Amphenol an advantage over the competition when it comes to best-in-class data rates. A key market for these high-end products is in the web service provider (WSP) and data center markets, markets that Amphenol supports on an international scale.
The customizable aspects of Amphenol’s cable assemblies are part of our everyday engineering and operational excellence and provide a further edge over our competition. EEPROM’s can be programmed per customer specifications, and can be write-protected to further enhance customer branding. From a production standpoint, our automated platform of assembly lines in our Xiamen, China and Mexicali, Mexico production facilities provide repeatability in an industry where capital requirements to stay abreast of the latest technology are the norm. Lastly, Amphenol’s fully integrated solution - from our own bulk wire provider, to cable assembly, connector assembly, and loopbacks for testing - is a one-stop solution that is a differentiating factor in our industry.