Hot answers tagged

67

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 ...


44

Main difference: Singlemode fiber has a lower power loss characteristic than multimode fiber, which means light can travel longer distances through it than it can through multimode fiber. Not surprising, the optics required to drive singlemode fiber are way more expensive, especially considering any varying circumstances. When to use each: Both singlemode ...


38

No, the numbers are right (Page 46). If I can reword your question, it's "Why should I use fiber if the propagation delay is worse than copper?" You are assuming that propagation delay is an important characteristic. In fact (as you'll see a few pages later), it rarely is. Fiber has three characteristics that make it superior to copper in many (but not ...


33

While most other answers have talked about Length limits, Interference issues and are all correct. One important factor while choosing the cable is the speed of the network and the devices you plan to use. The general specifications for currently available ethernet network speeds are as follows Twisted Pair Copper Cable Category 5e 10/100/1000BASE-T ...


31

Multi-mode fiber (MMF) uses a much bigger core and usually uses a longer wavelength of light. Because of this, the optics used in MMF have a higher capability to gather light from the laser. In practical terms, this means the optics are cheaper. Single-mode fiber (SMF) has much tighter tolerances for optics used. The core is smaller and the laser ...


27

Some devices could only run at 10 megabit/s, so the device at the other end would autosense the speed to match. If a device that has a maximum speed of 10 Mbit/s is connected to a 10 Mbit/s / 100 Mbit/s switch, the switch needs to lower its speed on that particular port in order to effectively (efficiently) communicate with the device. These ...


23

If cost is a factor for you, I would look at it like this; Scenario 1 If you are making a short run, say 50M, I would go for copper, simply because of cost (This 50M run is between two comms cabs in an office building for example). Copper is cheaper and using switches would save on the cost of SFPs or GBICs and so on. We obviously aren't talking thousands ...


22

Contrary to popular belief, there are cable color standards defined, just hardly anyone (myself included) follow them closely or at all. Check local jurisdictions for variants. ANSI/TIA/EIA-606-A Administration Standard for the Telecommunications Infrastructure of Commercial Buildings or the updated ANSI/TIA/EIA-606-B documents these standards. Generally, ...


20

It is used to split the outer shielding away without needing to use a sharp object which could potentially damage the wires themselves. It is commonly called a ripcord. Image taken from http://netx.us.com/Product%20pdf/Copper_Solutions/A6.pdf


19

This can introduce a number of problems, like additional attenuation or cross talk. Splicing is to be avoided whenever possible, but I have seen this work in a pinch although I would never recommend it. They key is to use a cable certification tester (not just a continuity tester) to make sure it still passes your required standard (Cat5/5E/6) after ...


18

If you ever feel that you are going to run FCoE over the medium then it is better to run fibre than copper as the BER for copper is significantly higher and most of the time will be outside of the tolerance for the 'lossless' nature of FCoe.


16

I will add another factor that hasn't been mentioned. I can quickly and easily make copper cables, measured and cut to the exact length I need for a run...resulting in neater cable plants. While you can cut to length and put ends on fiber optic cable, I find it considerably more difficult and time consuming...and my experience doing this is with multi-mode ...


16

When you use TIA/EIA-568B on both sides this is a straight through cable. The colors of the inner jackets don't really matter, much the same as it makes no difference to the operation of the network if you use a network cable with a black or yellow outer jacket. However, the standard is in place for a real reason, and that is that the cabling system should ...


14

Remember 10Mbps came first, then 100Mbps, then 1000Mbps. The advantage of supporting multiple speeds and automatically switching between them is you can upgrade your network gradually without having to worry about what speed each device supports or replacing everything at once. You just plug a device in and it connects at the highest mutually supported ...


12

Some things that I haven't seen mentioned: 1) 10GBASE-T uses a lot of power compared to fiber to DAC. 2) 10GBASE-T transceivers have much higher latency than other options. This could be important in a compute cluster or other low latency environment like automated financial trading.


12

Looking over the frequency spectrum, I notice that light is at a relatively low Hz rate as compared to high frequency. What spectrum chart were you looking at, because this is not correct. Here's a spectrum chart from Wikipedia: Notice higher frequencies are to the left, and longer wavelengths are to the right. In fact these are related by the formula f = ...


12

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 ...


12

A E said: OK @MikePennington, so what's the "right way"? Either hire a professional cable installer to check out your cable installation, or get something similar to a Fluke CableIQ. These meters perform detailed tests on the cable that reveal what you're dealing with. GigE has Signal to Noise requirements that simple continuity testers will not check. ...


12

Hi and welcome to Network Engineering. As for "delay" vs "latency": The terms are not always used consistently. Some hints may be found here. I think generally, the term latency is used when looking at end-to-end times for one direction, which essentially are composed of the sum of all propagation, serialization, buffering (and possibly processing) delays ...


11

[MMF] longer wavelength (850nm), much wider beam vs. [SMF] short wavelength (1310nm-15??nm), narrow beam. The key difference that no one has touched is "modal dispersion", which is a fancy term to describe how the light moves through the fiber. This page goes into far more detail. The first picture sums it up... MM is bouncing off the edge of the fiber ...


11

You'll find discussion of this elsewhere - see 'Why would I choose Copper over SFP+ for 10GbE?' - but broadly speaking SFP+ DA is, ignoring distance: Cheaper at the adapter side. Lower power and latency. Gives added flexibility if you need to move to fibre later. 10GBase-T on the other hand is: Cheaper at the connector side - patch leads being cheaper ...


11

Anything you choose to do will increase attenuation and potentially shorten the distance you can run PoE. There is no best practice answer to this as the best practice is to re-run the cable. Since you can't (or aren't willing to do this) then I would do one of two things, although I would still highly recommend running a new cable (you can use the old ...


11

Per the ANSI/TIA/EIA 568, Commercial Building Telecommunication Standard, UTP cabling is limited to 100 meters. That length assumes up to 90 meters of solid-core (better performance, but fragile) horizontal cable, and no more than 10 meters of stranded (poor performance, but less fragile) patch cord divided between both ends. Installation is critical, and ...


10

Adjusting the light frequency, theoretically will allow more data to transfer (i.e. UV -vs- IR) per unit time No this is not true. Please see this question's answer on the Electronics Stack Exchange site. The frequency of the light travelling down the fibre is not relational to the speed of data transmitted as you may think. I know that question I linked is ...


10

Here's a few things not yet covered. Using only single mode lets you use one fibre type for everything (fewer optics, cable types to spare) No likelihood of obsolescence (eg, OM3 seemed like it was current for ~3 years) Offers single-pair options for 40 & 100g Offers single-fibre options at 1 & 10g Although the optics are more expensive they're < ...


10

Please read Everything You Always Wanted to Know About Optical Networking – But Were Afraid to Ask :)


10

Lots of people have answered already; and I agree: Fiber beats copper as soon as distance becomes a factor. But beware of multimode fiber; it also has serious distance issues. You can only go 550 metres on GE (1000BASE-SX), and some of the 10GE modes manage 330 metres on really good multimode fiber (OM3 or OM4). In a larger colo or CO or in a campus ...


10

Cross on one of your patch cables. You want your installed fiber plant to be labeled correctly at both ends (Strand 1 at Site A = Strand 1 at Site B).


10

The colors are just there as an ease-of-use tool. What really matters from a functional standpoint is what cable is connected in the jack in what position. Electrically the colors of the wires make no difference. It will require care, but you can identify the wires per pair by "ringing" them out with a multi-meter with a continutiy check ( the symbol ...


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