These days both fibre and twisted pair are supporting 1000BASE-T and 10GBASE-T, but when do you choose one over the other? The obvious one is maximum cable length, but what are other factors which might come to mind when making this choice.
Ethernet – When to choose fiber instead of twisted pair (copper)
cablingethernetfiber
Related Solutions
Reasons to use shielded cabling
You asked about using shielded cabling to protect ethernet from interference from heavy power currents. We mentioned above that shielded cabling isn't required in this case, but there are a few valid use cases for it:
- If you run cabling where there truly is a high potential for interference, such as ethernet cabling that runs near aircraft radar transmitters.
- If you find that you're at the 100m distance limit for standard ethernet runs, it's not unheard of to squeeze a few more feet beyond the 100m limit of a Cat5e run by using shielded cabling. That said, the 100m distance limit is there for more than just cross-talk and noise limits, but some people still get away with doing this. It helps if you're in bind, but it's much better to lay out your IDFs correctly; you shouldn't do this intentionally.
It obviously won't hurt to use shielded cabling in your case, but it doesn't sound like you really need it.
Grounding Shielded Cabling - one side, or both sides?
As our 'porta cabin' only has 2 PC's we are not planning to put a patch cabinet in there, so my question is - if I terminate the STP cable to a socket and run a standard patch cable that side to a small switch (and then cables to the PC's) would I need some way to earth it?
Terminating one side of shielded cabling is sufficient and industry practice; I am assuming the shielded cabling is terminated correctly. Grounding shielded cabling is also discussed in BICSI Mythbusting: Shielded cabling, which I thought was a great presentation. If you only ground one side, you're eliminating the possibility of ground loops on the cabling itself. Ground loops tend to form at power-cycle frequencies, which don't interfere with ethernet; however, it's best to avoid ground loops altogether.
Terminating shielded cabling to a patch panel
The patch cabinet side would also be terminated to a socket (with patch cable going to main switch (with fibre link to our main office)). I have no STP RJ45 terminations (only standard UTP).
If I was to run an earth wire from the STP shield/screen to the patch cabinet would that be enough (cabinet grounded through equipment connected to a UPS)? I would also look to use ferrite chokes on the cable (to negate any outside RF interference it would pick up) if we found problems.
This is a little unclear without a diagram, but let's cut to the essentials:
- Ground one side of your shielded cabling
- If you terminate into a patch panel, use patch panels / modular inserts designed for shielded cabling because the mod plug (shown below) terminates to the shield inside the cable, and that all should be grounded.
Shielded mod plug:
Avoiding ground loops
As the same power source will be powering both ends of the installation I understand we won't have problems with earth differential.
This isn't in the critical path of your main questions, but it's worthy of discussion. Everything depends on whether the buildings are grounded individually, or whether the power cabling to your 'porta cabin' carries the ground conductor with the hot and neutral. If the buildings indeed have different ground rods, you could see a difference in ground potential between the buildings. Please see BICSI Mythbusting: Shielded cabling, which discusses why this shouldn't be a problem for your shielded twisted pair termination, but it's a point worth mentioning in case you run into other equipment grounding concerns; you should not intentionally form ground loops, if possible.
Data transmission use differential signalling, in pair two wires carry opposite polarity. It lower sensitivity to external interference and to cross interference (betwen different pairs in cable).
Pair 3,6 not adjacent only in jack. All other way it adjacent. In-adjacency in jack make low difference in interference, but make compatibility with phone, who use primary central pair (4,5)
As Tinti comment. If for transmission of differential signal used not twisted pair (it named split pair) cross talk raise dramaticaly and such link not work more that 10m. (UPD: not more that 10m in Full Duplex mode, that is auto detected in most cases)
Related Topic
- 1000Base-T Ethernet – Why It Is Limited to 100 Meters
- 10Gbps Ethernet – Why Does 10Gbps Ethernet Use PAM16 Encoding and DSQ128 Constellation
- Ethernet – Ethernet Flow Control vs Quality of Service
- Cisco – 1000BASE-LX/LH Receive Power Level Greater Than Transmit Power Level
- Mode Conditioning Patch Cables – Will They Help with This Issue?
Best Answer
There are a fairly large number of factors to consider and it is also important to accept that not all fiber is the same just like not all twisted pair is the same. Here are a few things that occur to me. Of course these may vary depending on environment.
Fiber: Much longer max distances, depending on specification and throughput. No electromagnetic interference. Note however that fiber comes in a large number of grades and planning for the future may be somewhat more complex.
Copper: Shorter max distances per link. Susceptible to electromagnetic interference. Fewer number of grades/variations (but still mind these!) meaning fewer accidents when the rollout team grabs the wrong spool (see below for a funny story). Supports power over ethernet.
Funny story: A particular county in a Western state runs a fiber network that began as a control system for their hydroelectric dams. As time went on they found they didn't need nearly as much fiber as was laid for this and so they separated out many of the strands and used it to build a county-wide network linking homes and businesses to ISP's and telco's. Of course single mode fiber was used for longer transmissions and multi-mode for short runs.
So when they were running the longer runs to connect towns and cities with this new network, the team that ran the fiber grabbed the wrong spool, and ran multi-mode fiber on all these long distance links. The team was quite unhappy when they found out they would have to re-run all the fiber again! Moral of the story: be very careful about ensuring that everyone knows which grades of fiber go where....