Active twinax cableThis matches with Cisco's compatibility matrix for 10Gb SFPs - passive cables length is up to 5 meters, and active cables length are up to 10m.
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. 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-the-rack switch over longer distances than passive copper cables.
How to distinguish active or passive twinax cable
There isn't a truly visual way to tell the difference between active and passive twin-ax cables. Active or passive twin-ax cable assembly and connects directly into an SFP+ housing. The active twin-ax cable has active electronic components in the SFP+ housing to improve the signal quality; the passive twin-ax cable is just a straight “wire” and contains no active components. Generally twin-ax cables that are less than 5 meters in length are active and greater than 5 meters in length are passive but this is a general rule of thumb and will vary from vendor to vendor. The connectors are the same and the cable jackets are identical. So how do you tell? Most manufacturers will have some sort of marking on the cable connector head which will identify the cable as active or passive. It is hard to tell by simply looking at it.
How to choose passive or active twinax cable
With all cables, length and signal strength are always something to look into. For shorter distances it is common practice to use passive cables, they are rated for ranges up to 5m and provide a good working solutions at a great cost. SFP+ DAC (Direct Attach Copper) passive twinax cable is suitable for very short distances transmission and offers a highly cost-effective and low power solution to connect within racks and across adjacent racks. SFP+ twinax passive cable allows for a serial data transmission up to 10.3Gb/s, which is a low cost choice for very short reach applications of 10GbE or 1-8G Fiber Channel.
When the distance between connection points that exceed 5m, it is highly recommended to use active cables to ensure signal is transferred all the way through. The cost may be a bit higher, but the signal is improved and gives peace of mind by creating a trustworthy connection.