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.

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.

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.

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.

Conclusion

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.

Difference Between Passive and Active Twinax Cable Assembly

Optical fiber cabling had gone through rapid development over recent years and maintained its leading role in telecom field. While twinax cable still remained a good way to access the networking industry trends over the last three decades and presented the highest longevity among all media. Twinax cable (see in following Figure) is a type of cable similar to coaxial cable that has two inner conductors instead of one. And owing to its cost efficiency, it is commonly used in short-range high-speed differential signaling applications. Currently there is a twinax cable which comes in either passive or active copper cable. So what is the difference between them? Today’s passage will provide a satisfying solution to you.

Describing Passive and Active Twinax Cable
A passive twinax cable carries a signal over short lengths (5m or under) of copper with no additional components to boost signal. While an active copper cable contains electrical components in the connectors that boost signal levels. This makes active copper cables a little more expensive than passive copper cables; however, they can connect the Converged Network Adapter (CNA) to a top-of-the-rack switch over longer distances than passive copper cables.

Why Implement Active Over Passive and Vice Versa?
Length and signal strength are always two important factors you should look into when requiring a cable for an application. Typically, we can see passive twinax cables being used between the server and the Top of Rack (ToR) switch. The upside in this configuration is that the passive twinax cabling connection is much cheaper than the cost of an optical link. The downside is that you are limited in distance and there’s also some cable interoperability issue you’ll need to deal with. Passive twinax cables are rated for ranges up to 5m and provide a good working solutions at a great cost.

When the distance between connection points exceeds 5m, it is highly recommended to use active cables to ensure signal is transferred all the way through. The downside is that they are more expensive and use more power. The upside is that you don't have to worry about distance (up to 300 meters) and, perhaps more importantly, you don't have to worry about which vendor’s cable you use and the signal is improved and gives peace of mind by creating a trustworthy connection. In regards to active versus passive twinax cables, it depends on what you are connecting together.

QSFP+ Copper Cables—A Cost-effective Application of Twinax Cable
QSFP+ direct attach copper cable assemblies offer a highly cost-effective way to establish a 40 Gigabit link between QSFP+ ports of QSFP+ switches within racks and across adjacent racks. QSFP+ Copper Cable is an extension of the established interface system SFP+ that is mainly used in short distance. 40G QSFP+ to 4SFP+ copper breakout cable and QSFP to QSFP copper direct attach cable are the two common types of 40G QSFP+ Copper cables.

QSFP to 4SFP+ copper breakout cables are suitable for very short distances and offer a very cost-effective way to connect within racks and across adjacent racks. Take QSFP-4SFP10G-CU1M as an example, this breakout cable connects a 40G QSFP port and four 10G SFP+ ports of Cisco switches and operates at a link length of 1m. While a QSFP+ to QSFP+ passive copper cable consists of a cable assembly that connects directly into two QSFP+ modules, one at each end of the cable. This cable use integrated duplex serial data links for bidirectional communication and is designed for data rates up to 40Gbps. There are various QSFP+ to QSFP+ passive copper cables branded by famous brands, like Cisco, HP, Juniper, Brocade, etc. The following picture shows a Cisco QSFP-H40G-CU3M Compatible QSFP+ to QSFP+ passive copper cable.

Summary
There isn't a truly visual way to tell the difference between active and passive twinax cables. Therefore when you are requiring a twinax cables, please follow the instructions that I have listed above or you should ask your vendors for expertise suggestion. Fiberstore offers a large variety of SFP+ Twinax cables and QSFP+ cables that are well tested and compatible with major brand. If you have any inquiry of our products, please feel free to contact us.