There are two copper cabling types defined for 10Gigabit Ethernet, one using the usual UTP cabling that must be at least Cat6 or higher standard. This table show the key differences.
| Connector (Media) | Cable | Distance | Protocol |
|---|---|---|---|
| SFP+ CU copper | Twinax | 10m | 10GBase-CX1 |
| RJ45 10GbaseT Copper | Cat6, Cat6A, Cat7 | 100m | 10GBaseT |
Why Twinax
The twinax cable uses a different signal propagation method, my understanding is that it’s more like a radio wave than an electrical signal. A UTP signal needs a lot of electronics to drive generate and receive the signal.
The end result is that Twinax uses much less power (something around 1 – 1.5W per port) compared to UTP (4 – 6 W per port). When you have a lot of ports this power consumption can be significant factor in design.
You can see this in Cisco UCS designs where it is recommended to use the Twinax cables from the server to the Nexus 5000 switch as a server to Top of Rack cabling solution (not entirely unlike Infiniband). Of course, your connections from the Nexus 5K to the network core are likely to fibre or UTP since the maximum distance of the twinax solution is only 10 metres.
The EtherealMind View
Twinax is an ideal 10GbE solution for server to Top of Rack switch connection. Since it uses less power and is more reliable that UTP solution as the cable is physically more robust and not subject to physical damage, an important consideration for 10GbE over copper. Any damage to the copper cable due to crushing or bending can cause intermittent failures on Cat6 cabling (although less likely on Cat6A).
But the main reason for choosing twinax for 10GbE is lower power consumption for server to top of rack connections for integrated storage and data networks.
We recently deployed a large number of Cisco Nexus 2148s (top of rack) with Nexus 5010s and used all 10GBaseCX1 interfaces. The primary reason to use the 10GBaseCX1 interfaces over 10GBaseSR was cost. We ended up saving a lot of money by using the integrated SFP+ and twinax cable as opposed to purchasing the individual optical transceivers (10GBaseSR SFP+) and then the fiber optic patches.
You do need to be aware of the current distance limitations. Cisco only supports cables up to 5m in length even though the spec allows for 10m.
Cheers!
Michael
Thanks for the tip.
So how do you find those NX2K fabric Extenders ? I can’t quite believe that they really work, and chatting with some people, no one really trusts them or the idea behind them.
We used them for a new data center build where we had to provide connectivity to 10 racks of big box servers. We did have a Nexus 5010 up an die on us within days but so far everything else has been working fine. At the time the 2148 was the only option available and so we had to also deploy some 2960Gs for the 10/100Mbps devices (iLOs, PDU/UPS, etc). Now of course the 2248 is available which provides 100/1000Mbps connectivity.
Cheers!
But see http://ow.ly/28KlI which discusses distance limitations of Cat 6 used for 10GBase-T
Yes, only 55 metres on Cat6 (from memory). Basically, you would not choose to run 10GBaseT for anything, you should use fibre for all 10GbE and above.
There is no, and never will be, copper support for 40GbE and 100GbE
To say there will never be support for 40GbE on copper is flat-earth thinking. The same was said of 10GbE on UTP and it is now the lowest cost and most flexible solution for 10 Gig. 40Gig standards for UTP are already under discussion.
“The twinax cable uses a different signal propagation method, my understanding is that itís more like a radio wave than an electrical signal”
In EM field theory every “electrical” signal carried by wires or other medium is an electromagnetic wave. The signal in a twinax or RJ45 cable is not different from this point of view.
It changes how it is carried, including dispersion, interference and so on.