angelina's blog

January 15, 2016

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? Todayâ€™s passage will provide a satisfying solution to you.

Twinax cable

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 thereâ€™s also some cable interoperability issue youâ€™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 vendorâ€™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 Cablesâ€”A Cost-effectiveApplication 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. TakeQSFP-4SFP10G-CU1Mas 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 CiscoQSFP-H40G-CU3MCompatible 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.

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