WIRED-TECHNOLOGIES

 OPTICAL FIBER CABLE

 This has been made conceivable by a network of cables which are laid under the ground and below the ocean. The cables which transfer most of the world's data are optical fiber cables. They are also used in medical equipment.Let's see how optical fiber cables work and how they have revolutionized the world around us. Optical fiber cable is made up of thousands of fiber strands. And a single fiber strand is as thin as a human hair. Optical fibers carry information in the form of light. Let's first learn some fundamental behaviors of light to understand the workings of optical fibers. The speed of light changes when it passes via a medium. And this change in speed is expressed by the refractive index. This variation and the speed of the light leads to another interesting phenomenon. Refraction, to understand what it is, let us carry out an interesting experiment. In this experiment, light passes through a prism. You can see that at the interface the light gets bent instead of going straight. This phenomenon is known as refraction. Refraction occurs when light passes from a medium with a one refractive index to one with another refractive index. The light bends towards the interface when it goes from a medium of high to one of low refractive indices. Refraction is the reason why a pencil looks bent in a glass of water. This simple refraction technique is effectively used in optical fibers. Now, let's make this experiment a hypothetical one. we are able to increase the refractive index of the glass in real time. As we increase the refractive index, the light will bend more and more towards the surface. After a time you can see that, the light will pass through the surface of the glass. If we increase there refractive index further, the light will suddenly comeback to the first medium as a pure reflection. This is called total internal reflection. The total internal reflection is possible if we increase the incident angle rather than increasing the refractive index. In this case at a certain angle called the critical angle, the light will come back to the first medium. This phenomenon of total internal reflection is used in optical fiber cables to transmit the light. The simplest form of optical fiber cable is shown here.

 Cylindrical glass with a high refractive index. If the laser strikes the interface at an angle greater than the critical angle, total internal reflection will happen and the light will reach the other end. This means that light can be confined in the optical fiber over a long distance. No matter what complex shape the fiber forms. Remember, total internal reflection happens between the high refractive index glass and the low refractive index air. However, optical fibers need a protective coating. A protective coating is not possible with this configuration.The introduction of protective material will replace the position of the air and cease the total internal reflection phenomenon. An easy way to overcome this issue is to introduce a low refractive index glass above the core glass known as cladding.This way total internal reflection will happen and we'll be able to use a protective layer. Both the core and the cladding use silica as their base material. The difference in the refractive index can be achieved by adding different types of dopants. The optical fiber we have just constructed won't be able to carry signals for more than 100 kilometers. This is due to various losses that happen in the cable. This loss of signal strength is generally called attenuation. Absorption and scattering are the main reasons for signal attenuation. This is why you see amplifiers and cables after a certain distance. They boost the signal strength and allow signals to be transmitted over a long distance. The power required for the amplifier is drawn from nearby sources. Now, back to the main topic, how does the optical fiber transmit information such as phone calls or internet signals? Any information can be represented in the form of zeros and ones. Assume you want to send a hello text message through your mobile. First this word will be converted into an equivalent binary code as a sequence of zeros and ones. After the conversion your mobile phone will transmit these zeros and ones in the form of electromagnetic waves. One is transmitted as a high frequency and zero as low frequency wave. Your local cell tower picks up these electromagnetic waves. At the tower, if the electromagnetic wave is of high frequency, alight pulse is generated. Otherwise, no pulse is generated. Now these light pulse scan easily be transmitted through optical fiber cables. The light pulses which carry the information have to travel through a complicated network of cables to reach their destination. For this purpose, the entire globe is covered with optical fiber cables. These cables are laid under the ground and below the ocean. It is mainly the mobile service providers that maintain these underground cables. AT&T, Orange and Verizon are some of the few global players who own and maintain the submarine cable network.

 

 A detailed cross section view of an undersea cable is shown here. You can see that only a small portion of the cable is used for holding the optical fiber. The remaining area of the cable is a mechanical structure for protection and strength. Now the question is, where does the amplifier get power from under these deep oceans? Well, for this a thin copper shell is used inside the cable. Which carries electric power along the cable so that the amplifiers can be powered. This whole discussion simply means that if optical fiber cables do not reach a part of the globe, that part will be isolated from the internet or mobile communications. If we compare optical fiber cable to traditional copper cable,the optical fiber cable is superior in almost every way. Fiber optic cables provide larger bandwidth and transmit data at much higher speeds than copper cables. This is because the speed of light is always greater than the speed of electrons. The flow of electrons in a copper cable generates a magnetic field even outside of the cable that can cause electromagnetic interference. On the other hand, the light which travels through the optical cable is always confined within the fiber. Thus the chance of interaction with an external signal does not exist. One more interesting feature about optical fiber cables is that any light signal which enters from the side has a minimal chance of traveling along the cable. Thus the optical fiber cables provide high data security. You might be amazed to know that optical fiber was first used in endoscopy even before it was used in the telecommunications field. In telecommunications,digital pulses are transferred through the optical fiber cable. However, in endoscopic cables, visual signals which are on the analog form are transmitted to the other end. 

 TWISTED PAIR CABLE

 

 

Twisted pair network cables are constructed from four pairs of wiring, contained within an insulating sheath. Each pair of wire is twisted together with slightly different twist rates. This twist in the pairs reduces the opportunity for the electromagnetic interference from outside sources or from other pairs of wires.Now, this interference that can be caused by adjacent pairs is called crosswalk. Each pair of wires is color coded with the common coloring scheme being white orange/orange,white blue/blue, white green/green, and white brown/brown. Now, these twisted pair cables can be either shielded or unshielded, that’s STP or UTP.Now, shielded twisted pair has an additional shield that is either wrapped around eachpair of wires, or around all four pairs. STP reduces the opportunity for EMI or crosstalk,but it is a little more expensive and a little harder to work with. The shielding reduces the flexibility in the cable. Now, UTP, unshielded twisted pair, is deployed in the network much more often than STP is. Now UTP and STP can come in plenum grade or non-plenum grade twisted pair. Building codes often call for plenum cable, plenum grade cable, to be run in the plenum space. Now, the plenum space is an area that is designed to assist in airflow of a building for HVAC purposes. In a plenum cable, the outer jacket is either made from a fire-retardant cover or low smoke PVC material. This outer cover makes these cables a little less flexible and more expensive. Quite often, plenum cable shave a polymer or nylon strand woven into them. This helps to take some of the hanging weight of cables. This reduces the chance for cables to stretch, which can cause the pairs of wires inside to break. Now, let’s move on to some characteristic sand categories of twisted pair. A twisted pair network cable is designated as either being a straight through or a crossover cable. A straight through cable is a cable in which the wiring scheme is the same on both ends. That wiring scheme is called the pin out, they're used to connect dissimilar types of devices, like a PC to switch or switch to a router.The crossover cable, on the other hand, uses a different pin out on the cable ends.

 They're crossed over from end to end. The crossover cables, they’re used to connect similar types of devices, like when you need to connect a PC directly to another PC or a switch to a switch. Although, now it is common for the network ports to be able to auto-sense what they connect to and they can make the switch internally.Now, twisted pair can have different types of conductor construction. They can have a solid conductor, that’s where the core of each wire is made from a solid copper conductor.These are strong and sturdy and they work really well for pulling twisted pair through walls. But there are two things with solid conductor cables; they have reduced flexibility and they tend to be more expensive. The other type of construction is stranded conductor.The core of each wire is made from small thin strands of copper that are twisted together.They are not as strong or as sturdy as solid core wire, but they are much more flexible than solid core and work really well with patch cables. Now, let’s move on to categories of twisted pair network media. Twisted pair network cables are broken out into categories based on their maximum rated ability to handle network traffic.Most of the bandwidth gains in the categories are due to the changes in the twist rate in the pair. More twists in a pair of wires reduces EMI and cross-talk, allowing for more speed-across that pair. There are five currently different categories of twisted pair network cables that are readily available. There’s CAT3, CAT5, CAT5e, CAT6, and CAT6a. Unless otherwise specified, the maximum distance of a twisted pair cable segment is 100m. Now, let’s move on to those categories of cables in a little more depth. And we begin with CAT3. Now, this is rated for up to 10 megabits per second in speed, that’s 10baseT networking. It’s not really used in the LAN anymore, in the local area network, but it is still used for telephony, for running telephone line. CAT3 was replaced by CAT5, 

 

which is rated for up to 100 megabits per second in speed,that’s 100baseT networking. CAT5 couldn’t keep up with modern networking, so along came CAT5e. It’s rated for up to 1 gigabits per second, that’s 1000baseT networking. And of course, technology moves on we had to come up with CAT6. It’s rated for up to 10 gigabits per second, that’s awfully fast by the way. That’s GbE, or 10 gigabit Ethernet networking.Now, to achieve that 10Gbps speed, your maximum cable length on a CAT6 cable could only be55 meters. Well, they found that it was not quite long enough, so they came up with CAT6a. Now, it has the same rating as CAT6, but your segment can be up to 100 meters long and still achieve those gigabit Ethernet speeds.Now, that concludes this session on twisted pair network media. 

 

There are many types of cables like Cat5, Cat5e, Cat6 and Cat6a  First of all, what the heck are these "Cat"ratings  for Ethernet cables, that stands for Category, and the different numbers represent different standards and identification for the cable, so you can think of them like different versions. all of these cables will typically "work", since the new versions are all backwards compatible. They all use the RJ45 connector, often just called an "Ethernet port", but the difference is in the rated performance of each.So let's go over all the different types of Ethernet cables you may come over, from Cat5 all the way through Cat7 and beyond. The first type is really common, which is"Cat5". However, these days when someone says Cat5,they usually are referring to Cat5e, but we're getting ahead of ourselves. Now a true Cat5 cable is actually obsolete,and you probably can't even buy them any more. A cat5 cable is only rated for up to 100mbpsat 100 meters, with a 100 MHz bandwidth.So obviously only being rated for 100mbps,you almost never see these anymore, and if you're still using one, you should definitely replace it. Which lead us to Cat5e, or Category 5 "amplify". Cat5e is very common these days, and it is assess for 1 gigabit speeds at 100 meters, with a bandwidth of 100 MHz. This is due to improved specs regarding twisting of the wire pairs inside, shielding, and improvements which reduce "cross-talk" or intrusion,which would reduce speed. Also, a regular Cat5 cable only required 2 twisted pairs of wires, while Cat5e uses four, so clearly  it can transfer much more data. Though it is important to note that just rating certifications are for bare minimum, so it's very possible that a cable will be capable of much
 more than what it's rated for. 

Cat6 further reduces cross-talk, using tighter wound wire pairs, and may also use things like a plastic core to better separate the internal wires. This is especially so if the wire can't easily be replaced, like if you're wiring a house, where I would get at LEAST Cat6  But, if you're just buying a general purpose cable for your laptop or something, Cat5e would definitely be fine, since
I doubt any of your devices are capable of 10 gig anyway. So by now you might be thinking, OK surelyCat6 is the best.I mean why would you need anything more than that? Well, you may be right, but we're not stopping there! Because there's also Cat6a! This one is also capable of 10 gigabit, but at a longer maximum distance of 100 meters instead of 55, and it has a larger 500MHz bandwidth.If you are actually running a 10 gigabit network,Cat6a will be more reliable at getting your full speed, since again it has further improved specs for reducing cross-talk.And now finally, the big daddy of Ethernet cables,
is Category 7. As far as I could tell, this is the fastest type you can buy at the moment. Cat7 is also rated for 10 gigabit speeds,but with an even larger bandwidth of 600MHz, and the strictest specifications for reducing cross-talk, such as requiring shielding between individual wire pairs, as well as the whole cable as itself. This seems to be all about improving reliability,since it doesn't actually improve the speed requirement, even though it probably is capable of higher speeds if you had a switch that was
 capable of faster than 10 gigabit.

 

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