QSFP+ Direct Attach Cable (DAC) Cables – Optimal Solution for 40G Interconnect


Believe it or not, the era of 1G or 10G Ethernet has already passed, and here comes the 40GbE. IEEE introduced the 802.3ba Ethernet standard in June 2010, since then enterprises like Cisco, HP and Juniper have devoted themselves to the development of 40G technology. A number of routers, switches, and network cards already operate at this speed. 40 GbE runs on Quad Small Form Factor Pluggable (QSFP+) cabling, which is the most common 40G optical solutions. 40G DAC cable provides a cost-effective solution for high-density network connectivity. In today’s blog, we are going to focus on some basic information about 40G direct attach cables.

QSFP+ Direct Attach Cables

Direct attach cable (DAC) is a form of high-speed cable with “transceivers” on either end used to connect switches to routers or servers. It is a kind of optical transceiver assembly. DAC cables are not real optics and their components are without optical lasers, which makes them much cheaper than the regular optics. Because of their low cost, low power consumption and high performances, DAC cables are the preferable choice for storage area network, data center, and high-performance computing connectivity. Note that QSFP+ DAC cables can only support a distance within 7 meter.

QSFP+ Direct Attach Cable (DAC) Cables – Optimal Solution for 40G Interconnect 1

DAC Passive Copper Cable

QSFP+ DAC cables are designed in either active or passive versions. They are widely available for short-reach 40G interconnect. 40G DAC cables transmit 40GbE over short distances of parallel coaxial copper cabling. It uses a special cabling assembly with four lanes of coaxial cabling. Each transmit 10 Gbps in one direction and four transmit 10 Gbps in the other direction for a total data rate of 40 Gbps. QSFP to QSFP and QSFP to 4SFP+ copper direct-attach cables are the two common types of 40G DAC cables.

For example, Juniper QFX-QSFP-DAC-3M is the 40G QSFP+ to QSFP+ copper direct-attach cables. It is suitable for a distance of 3m and transmit over passive copper cables for 40-gigabit link. Cisco has also launched a 40G QSFP+ DAC cables for a distance of up to 3m. QSFP-H40G-CU3M, as the name implies, it can support a link distance of up to 3 m. Besides these two QSFP to QSFP DAC cables, many other telecom vendors also offer relevant 40G DAC cables. Just remember to find the suitable one matched with your switch or routers.

HP JG330A is QSFP to 4SFP+ copper direct attach cable. It connects with a QSFP+ connector on the one end and 4 SFP+ connectors on the other end, which are available in 40GBASE-CR4 and 10GBASE-CU standard. The following image shows a HP JG330A. You can take a closer look at it.

QSFP+ Direct Attach Cable (DAC) Cables – Optimal Solution for 40G Interconnect 2

40G AOC Cables

Active optical cables is short for AOC. AOC uses electrical-to-optical conversion on the cable ends to improve speed and distance performance of the cable while mating with electrical interface standard. Compared with direct attach copper cables, its smaller size, longer transmission distance, lower insertion loss and electromagnetic interference immunity make it popular among subscribers.

QSFP+ Direct Attach Cable (DAC) Cables – Optimal Solution for 40G Interconnect 3

A debate that whether you should choose optical cable over cooper or verse is the long-term unresolved problems existed in telecommunication industry. Just like that, people are wondering whether to choose passive or active version of fiber optic cables. Passive cabling provides a direct electrical connection between corresponding cable ends and it contains no active components to boost signal. Active cables provide the same effect, but by embedding optics and/or electronics within the connectors, can overcome some of the limitations of passive cables. While passive cables are always copper-based, active cables can use either copper wire or fiber optics to provide the link between the cable ends.


40GbE was given birth in 2010 in order to meet the increasing needs of higher bandwidth. 40G Direct Attach Cables cables, as an optimal solution to support 40GbE interconnect, were warmly welcomed by network designers who want to upgrade to 40G. Fiberstore supplies various kinds of DAC cable assemblies including 10G SFP+ Cables, 40G QSFP+ Cables, and 120G CXP Cables. We provide a full range of 40G QSFP+ DAC cables that are fully compatible with major brand. If you have any requirement, you can contact us.

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