All You Need to Know about QSFP Cables

In the field of data communications, there are different small form-factor pluggable (SFP) network interface modules used for fiber-optic cabling. These are modular slots that are used for media-specific transceivers so that they can connect a fiber optic or copper cable.

SFPs have the advantage of allowing individual ports to be equipped with a suitable transceiver as needed when compared to fixed interfaces. There are different types of SFPs and one type that is a bit large is the QSFP. You can learn more about SFPs here.

What is QSFP?

QSFP is an acronym for Quad Small Form-factor Pluggable. These are types of cable assemblies and connectors that share a type of mating interface. A mating interface is when two separate pieces of a connector system are put together so that they interconnect.

The mating interface of QSFP is a card edge that finds its root in a multi-source agreement referred to as INF-8438i. A card edge interface refers to the end of a circuit board that contains exposed and plated pads. It is these pads that make contact with the beams of the mating connector.

QSFP has four lanes which make it four times faster than other SFPs. It also comes in different variants with different speeds which can reach up to 200 GBit/s as in the QSFP56. QSFP is hot-pluggable and it is a compact transceiver that is available for use both in single-mode and multimode.

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A QSFP cable assembly is applicable for use in data centers, Infiniband, 40G Ethernet and networking devices like switches, patch panels, servers and host card adaptors (HCA).

Connectors and Cables

Connectors and Cables

The QSFP connector comes in a small size (which is 12.5mm x 18.2mm x 5.6mm) but it is not used by itself. It has a press-fit cage that is used over the connector. This is used to guide as well as latch the cable assembly. Sometimes, you can find some arrays where the cage has been integrated into the connector and they can be placed on the printed circuit board simultaneously. Generally, QSFP cables can be plugged into a QSFP or QSFP DD connector but QSFP DD cables can only be plugged into QSFP DD connectors.

There is a pull tab that can be customized to any shape, color, or size attached and it is used to unlatch the cable when it is pulled.

Several options or configurations can be used with the connector and cable assembly. They also have different performance levels. A connector cage could have between 1 to 6 connectors. This could either be a row of 6 columns or two rows of 3 columns. This can give room for one to configure a switch that has 36 ports in several ways. If you so choose, you can use a 1×6 or 2×3 connector and cage in a belly to belly arrangement or you can mount them on the same layer respectively.


QSFP interconnectors can include active optical cables (AOC), direct attach copper (DAC), active copper cables (ACC) and optical cables. Of all these, the DAC is the least expensive.

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Direct Attach Copper (DAC)

DACs connectivity depends on signal conditioning it gets from the host. The maximum length that can be achieved is dependent on the insertion loss of the assembly. This is determined by IEEE specifications. The cable insertion loss is defined by the length as well as the gauge (AWG). Also, the wire size is inversely proportional to its AWG.

Active Optical Cables (AOC)

Active optical cables are those that utilize permanently attached optical fibers rather than copper cables. Its modules contain VCSELs, transimpedance amplifiers as well as lenses that are used to change electrical signals from the host to light. At the receiver’s site, the light is again converted to electrical signals before it leaves the module. This process typically gets its power from the host. Also, because the efficiency of the modules is not 100%, there is power loss due to heat. This can be removed by fans and heatsinks.

You can find the advantages of AOCs over DACs here

Active Copper Cables

Active Copper Cable (ACC) feature amplifiers and integrated signal conditioning. This helps it to overcome losses due to the copper cables. This means that despite the same AWG, they can have a longer length than DACs. That is for the same length of cables, ACC will utilize a smaller AWG than DACs. This helps to increase the flow of air. The host will typically treat ACCS the same way it would AOCs. It also needs to make up for losses from the integrated circuit to the module. ACCs are less expensive than AOCs and uses less power from the host.

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There are different form factors available and with different capacities. QSFP is one of them. It comes in different variants and has a lot of advantages to using it. If you are thinking of handling high-end data, then it is one of your go to choices.

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