Do You Know About Twinax Cable?

21. july 2017 at 11:42
Introduction to Twinax Cable
A twinax cable (also called twinax or twinaxial cabling) is a type of cable similar to the common coaxial copper cable, but has two inner conductors instead of one. Twinax cable was initially designed by IBM, so it has been primarily used by IBM for its IBM3x and AS/400 computer systems. But until now, the cost-effective twinax cable has been widely used, especially for applications that require high-speed differential signaling in a short-ranged scenario. They are suitable for networking, storage, and telecom industries. They are used in applications such as data center cabling infrastructure, SAN, NAS, other storage servers.

Its main advantages were high speed (1 Mbit/s versus 9600 bit/s) and multiple addressable devices per connection. The main disadvantage was the large connectors that usually needed screws to stay in place. The twin conductors of the twinax cable do not carry individual signals. The cable works in a half-duplex mode, as both connectors are required to transmit data.

Difference Between Active and Passive Twinax Cable
Currently there is a twinax cable which comes in either passive or active copper cable. So what is the difference between them?

A passive twinax cable carries a 10 Gig Ethernet signal over short lengths (5m or under, like SFP+ passive cable) of copper with no additional components to boost signal. An active twinax cable carries a 10 Gig Ethernet signal over long lengths (5m or more, like XFP active cable) of copper with the use of signal boosting technology. Passive copper cables contain no electrical components. While active copper cables contain electrical components in the connectors that boost signal levels. This makes active copper cables slightly more expensive than passive copper cables; however, they can connect the Converged Network Adapter (CNA) to a Top of Rack (ToR) switch over longer distances than passive copper cables.

How to Tell Active From Passive Twinax Cable?
Active and Passive Twinax Cable
We can see from the above picture that they look totally the same, and there isn't a truly visual way to tell the difference between active and passive twinax cables. The connectors are the same and the cable jackets are identical. So how do you tell? Most manufacturers including FS.COM will have some sort of marking on the cable connector head which will distinguish the cable as active or passive. But it is also not simply to tell by just looking at it.

Which to Choose?
With all cables, length and signal strength are always something to consider. For shorter distances, passive twinax cables are preferred, they 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 twinax cables to ensure that signal is transferred smoothly. The cost may be a bit higher, but the signal is strengthened.

Typically, we see twinax copper cable being used between the server and the Top of Rack switch. In regards to active versus passive twinax cables, it depends on what you are connecting together. For example, if you are connecting a CNA to a Cisco ToR switch (Nexus) and the cable length is 1, 3, or 5m, you can use a Cisco-supplied 1, 3, or 5m passive twinax cable, which is offered by FS.COM at a great cost and performance. If you are connecting a CNA to a Cisco ToR switch (Nexus) and the cable length is 7 or 10m, you need to use a Cisco-supplied 7 or 10m active twinax cable. If you are connecting a CNA to a Brocade ToR switch (8000) and the cable length is 1, 3, or 5m, you can use a Brocade-supplied 1, 3, or 5m active twinax cable.
Cisco Nexus 9300 Series
Conclusion
This post gives a brief introduction to twinax cables, including its definition, application, the difference between active and passive twinax cables, how to tell from them and which to choose when they are needed. However, there isn't a truly visual way to tell the difference between active and passive twinax cables. Therefore when you are requiring a twinax cable, please follow the instructions that I have listed above or you should ask your vendors for expertise suggestion. FS.COM offers a large variety of SFP+ Twinax cables and QSFP+ cables that are well tested and compatible with major brand.
 

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