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I'm venturing for the first time into the 10 gigabit (over copper) realm. Likewise, I have never worked with shielded CAT-5/6 cables previously. From my own research, I understand the types and benefits of shielding when it comes to long runs of network cable, such as between a patch panel and a wall jack in an office.

I'm less clear about the use of shielded patch cables (<15ft), particularly when the cable is connected directly from a server to a switch with no patch panel in between (i.e. nothing to ground the cable). This will be my situation when we purchase a few Dell PowerConnect 8164 switches, install them at the top of our server racks (facing the rear), and install Intel X540-T2 NICs in the servers.

Here's what I'm trying to figure out:

  1. Is there any benefit in using Cat-6A over regular Cat-6 stranded patch cables?
  2. Is there any benefit in using shielded (e.g. S/FTP) cables? I know this is related to EMI and some other environmental factors, but I have no way of measuring this.
  3. When a shielded cable is connected directly from the server to the switch, are there some additional electrical requirements that one or both sides must support?

Thanks!

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2 Answers 2

up vote 4 down vote accepted

A shielded cable main purposes are:

  1. To make sure that any electrical discharge (even one from a wool blouse would produce) doesn't get accidentally sent into your TX or RX wires and burn some chip/board/system but redirected instead through the shield into the closest ground.
  2. To lower error rates due to signal noise.

If none of your gear has a grounded plug avoid using shielded cables or connect some grounding alligator clamps at the ends.

Using shielded wires over short distances might be overkill but it should provide peace of mind when buying expensive network gear!

UPDATE:
Model 'PowerConnect 8164' is a grounded network gear with grounded sockets.
You'll recognize a grounded socket if it's also encased in a metallic sheet.
If the switch's chassis is connected by a grounding wire to the rack, means the switch itself can be grounded. (if it would have only plastic RJ45 sockets that would't protect it's insides by some discharge travelling over the wire, not your case)

A grounded plug has a metal casing over the normal plastic plug (you connect the 9th wire aka. 'ground' to it by bending it over the jacket).

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The "grounded plug" is precisely what I'm trying to understand. I've yet to see any switch specs that mention grounding of the network ports. Wouldn't any port be grounded if the switch chassis is connected by a grounding wire to the rack? Or does the actual port design need to change to support shielded cables? –  VokinLoksar Jan 4 '13 at 13:08
    
updated my answer to include your questions –  CSᵠ Jan 5 '13 at 22:27
    
Thanks for that explanation! –  VokinLoksar Jan 5 '13 at 22:29
    
Eh, the wires in copper Ethernet are connected by transformer to the NIC, you'd have to send one heck of a ESD through them to damage (the first one I looked up has a 2kV continuous rating). The shielding is pretty exclusively for noise, specifically in the MHz and a multiple of the symbol baud. –  Chris S Jan 6 '13 at 5:17
    
Every rackmount switch I've seen has grounded ports for use with STP. Most also have a separate grounding lug; this is used for creating a common ground for all associated equipment. If it does have a grounding lug it should be attached (if you don't have a single point grounding system then attaching it to the rack or UPS's ground is sufficient). Most small/medium office buildings have a single ground system so it's not necessary to consider the point of ground attachment. –  Chris S Jan 6 '13 at 5:20

To answer you questions....

  1. Cat6A is required for 10GbE connections. Cat6 is an old spec and only runs at 1GbE speeds. There's plenty of history there, but Cat5e = 1GbE, Cat6a = 10GbE, Cat7a = 40GbE (and 100GbE over very short runs).

  2. Shielded cables block more EMI than just the twists in the pairs. The twists are great for low frequency interference, but don't work well against MHz level EMI. This sort of interference is pretty rare, but happens in certain industrial situations and more commonly around large radio equipment.

  3. There's no special requirements of the switch or NIC. Any business grade equipment should have a metallic shield at the port so the metal shield on the cord has an open-drain. It's not necessary for proper operation, but does make the shielding more effective.

Unless you've got some odd equipment in your rack (like high powered radios or similar) that shielded cables are not necessary and would be of no benefit. The rack is likely already surrounded by grounded metal, there's unlikely to be a source of significant EMI in the first place, and the short run all reduce any potential gains from using shielded cables.

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+1 for the cabinet rack info, I was thinking about open racks without a back metal sheet and maybe a front glass door –  CSᵠ Jan 6 '13 at 7:47

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