40G QSFP+ DAC Overview – QFX-QSFP-DAC-3M and QSFP-H40G-CU3M

Evolution is taking placing every minute in the data center in order to better meet people’s needs, and one of the main changes in the data center is that data center designers want to migrate to 40G or 100G without replacing the existing multimode cabling infrastructure. It is known that every data center requires optical transceivers and Direct Attach Cable (DAC) for interconnect. Recently many vendors supply 40G optical devices including QSFP+ optical transceivers, QSFP+ DAC cables and QSFP+ AOC cables. The QSFP+ DAC cables from Cisco and Juniper are highly favored by overall users. Thus in today’s article, we will pay more attention to the illustration of the 40G QSFP+ DAC cables, especially the Juniper QFX-QSFP-DAC-3M and Cisco QSFP-H40G-CU3M.
40G QSFP+ to QSFP+ Direct Attach Copper Cable
QSFP+ to QSFP+ direct attach copper cable offers a highly cost-effective way to establish a 40G link between QSFP+ ports of QSFP+ switches within racks and across adjacent racks, which is very suitable for very short distances application. These cables connect to a 40G QSFP port of a switch on one end and to another 40G QSFP port of a switch on the other end. Supporting similar applications to SFP+, these four-lane high speed interconnects were designed for high density applications at 10Gb/s transmission speeds per lane. One QSFP+ to QSFP+ direct attach copper cable link is equivalent to 4 SFP+ cable links, providing greater density and reduced system cost. The following image presents an inner structure of QSFP+ DAC cables.
QSFP+ DAC cable
There are two QSFP+ DAC cables available on the market—Passive and active QSFP+ to QSFP+ direct attach copper cables. With an active QSFP+ to QSFP+ direct attach copper cable assembly, the connection is capable of distances of up to 10 meters, while with a passive QSFP+ to QSFP+ DAC cable assembly, the connection is capable of distance of up to 7 m. QSFP+ passive DAC cables are hot-removable and hot-insertable. This cables use integrated duplex serial data links for bidirectional communication and are designed for data rates up to 40 Gbps. Passive DAC cables have no signal amplification built into the cable assembly. The following part will illustrate two passive QSFP+ DAC cables—QFX-QSFP-DAC-3M and QSFP-H40G-CU3M.
  • QFX-QSFP-DAC-3M
This Juniper quad small form-factor pluggable plus (QSFP+) DAC cables are suitable for in-rack connections between two QSFP+ ports. It is suitable for short distances of up to 3 m, making itself ideal for highly cost-effective networking connectivity within a rack and between adjacent racks.
  • QSFP-H40G-CU3M
This is also a QSFP+ DAC cable just like QFX-QSFP-DAC-3M, but it is from Cisco. As the name implies, it can support a link distance of up to 3 m. Cisco QSFP to QSFP copper direct-attach cables are suitable for very short distances and offer a very cost-effective way to establish a 40GbE link between QSFP ports of Cisco switches within racks and across adjacent racks. To sum up, these two QSFP+ cables have the same performance but used on different Switch brand. Next, a short description about how to use QSFP+ DAC cables will be shown to you.
How to Use a 40G QSFP+ Direct Attach Copper Cable
As we known, QSFP+ DAC cables can be mainly divided into two types. One is QSFP+ to 4 SFP+ direct attach breakout copper cable, and the other is QSFP+ to QSFP+ direct attach copper cable. In fact, there is a third type called QSFP+ to 4 XFP breakout cable. However, regardless of what type of cables, they are both used to connect switch to switch or switch to sever. For a QSFP+ to 4 SFP+ direct attach breakout copper cable, it has a QSFP+ connector on one end and four SFP+ connectors on the other end. In terms of a QSFP+ to QSFP+ direct attach copper cable, it has a QSFP+ connector on both ends of the cable. When we use a fiber optic transceiver and patch cable to establish a fiber link, we should firstly plug the transceiver to the switch and then plug the patch cable to the transceiver (see in Figure 2). But for a QSFP+ direct attach copper cable, either SFP+ connector or QSFP+ connector, can be both directly inserted into the switch and don’t need a transceiver at all, which provides a really cost-effective solution for interconnecting high speed 40G switches to existing 10G equipment or 40G switches to 40G switches.
40G-QSFP-Direct-Attach-Breakout-Copper-Cable
Summary
There are many other vendors offering QSFP+ DAC cables. I can’t list all of them here for you to choose from. Cisco and Juniper QSFP+ DAC cables, as a representative of the QSFP+ DAC cables have been introduced in this article. Just remember that DAC cables must be compatible with the Switches of the network. In fact, the Switch market has been monopolized by large vendors like Cisco, Juniper and HP. And all the original optical transceivers from them are also very expensive. Therefore people are turning to purchase from OEM vendors for the competitive price and high performance. If you are thinking about upgrading to 40G network, QSFP+ DAC cables like QFX-QSFP-DAC-3M and QSFP-H40G-CU3M are indispensable. Fiberstore provides full series optical transceivers and DAC cables with a life time warranty and full compatibility. If you have any requirement, please send you request to us.

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