In this unit we're going to see the second part of wired networks and the media that supports them. And we're going to start with structured cabling. In the late eighties computer networks were becoming ubiquitous and a United States Industry Association, called Telecommunications Industry Association (TIA) that's and offshoot of the Electronic Industries Alliance (EIA) developed a standard for structured cabling that change completely the computer network business. In nineteen ninety one the first version of TIA/EIA-568 standard was developed and today we are in revision C. It has become so popular that ISO has adapted it and it has become an international standard that's calledISO/IEC 11801. Is not exactly the same but is very, very similar the idea was to create a standard for structured communication cabling in comercial buildings and its connections in a campus environment that separates network hardware characteristics from the cabling characteristics, how do they do that? by guaranteeing a minimum performance of the cabling system up to a given distance. That way the hardware designers can design their hardware without bothering about how cables are going to be because they are going to meet one standard. How do they do that? They define a channel that's formed by the patch cords, the patch pannel, the connectors and the cables that is between one station and the electronic that serve it and they set a minimum performance for this channel. The standard also defines a hierarchical structure in which every desktop station is connected individually to a floor cabinet. And then this floor cabinets are connected to a building cabinet and, if there are several buildings, the building cabinets are connected to a central campus cabinet. The connection between desktop and floor cabinet is done using twisted pair cables, that can be connected to a data network equipment or to regular telephone. So only one type of cable serving voice and data. If we have a voice pbx that is different from the data system. Then, the connection between floor cabinets and the building cabinet is made with fiber optic cables and/or twisted pair cables. Usually you will find a combination of both if cabinets are not too far one from another, so if they are too far we'll only use fiber optics. And the campus backbone is composed of multimode and or single mode fiber cables, depending on the distance and the capacity we want. If there's a traditional pbx, then the links between cabinets can also be completed with multi-pair telephone cables to send the telephone extensions to the different cabinets. There is also a maximum distance for a channel that it's one hundred meters and, as you have to take into account the patch cords in both sides, there is a maximum distance of ninety meter between the cabinet and the desktop connection. To connect the desktop stations we're going to see which cables are used. To connect the desktop stations with the floor cabinet a twisted pair cable with four twisted pairs is used. Every twisted pair consists of two individual copper wires that are twisted one over another, so signal cross-talk is minimized with adjacent pairs. These four pairs are wrapped in an insullation material, usually plastic and in some cases they have a conducting shield per pair (then is called STP for Shield Twisted Pair) or all the pairs have a common shield, then is called Foiled Twisted Pair or FTP. That's done to minimize interference The connector used in both cases has eight wires and is called RJ-45. UTP cables are easier to connect and to install and cables and connectors are less bulky, so most of the installed cable system use UTP cable instead of STP or FTP. Cable and components used, that's it patch cords, patch panels and connectors are assigned a category that depends on its quality and if everything is installed following the standards, that guarantees a minimum channel quality and a minimum bandwidth, for example for the minimum category that's now included in the current standards, that is Cat.3 components, the system guarantees a sixteen MHz bandwidth up to one hundred meters. Now this cables are used only for voice, for telephony. With Cat.5e (for enhance) components guaranteed a one hundred mhz bandwidth up to one hundred meters and that is enough for fast ethernet and for gigabit ethernet. In fact this is the lowest category that is used nowadays for ethernet communications. There are also category six, category six A, that is able to support 10Gbit per second ethernet, category seven and category eight components for example. And each of them is able to work at higher frequencies than the lower category. Other cables that are included in structured cabling, but are also used for wired networks and it's being used by operator, are the fiber optic cables. They are used nowadays in a lot of applications and are made of silica glass, are light, cheap and very durable. Just if you haven't seen any, the diameter of one optical fiber is slightly higher than a human hair. Several fibres are bundled together in a fiber cable that also includes all the components to protect them and to make them stiffer for example, a cover to protect them from external agents. It uses light to transmit information and has a very very high bandwidth and low attenuation, so it can carry a lot of information at very long distances. Another advantage is that it is not influenced by external electromagnetic fields so it is inmune to interferences. Single fiber links in commercial operation today can carry up to one hundred gigabytes up to forty kilometers from the transmitter, So they are very high-capacity systems that go very far. They work by guiding light inside the fibre and to do so they use a variation of the refraction index of the fiber along its diameter, so the light is reflected inside without going out. There are two main types of fibers multi-mode fibers that can use cheaper light sources that are usually based in leds and have less bandwidth and attenuate more the signal, so they are used in shorter distances and single-mode fibers that use more expensive light sources usally based on lasers and have more bandwidth and less attenuation. So they are used for higher capacity systems and longer distances. Fiber cable materials are cheaper than the copper used for twisted pairs, but the associated electronic is much more expensive and the connectorization process is more difficult and so more expensive. So they are used for backbone and in situations where very high bandwidth is needed in one or in several desktop stations or if there are electrical interferences or circumstances that can disrupt other type of communications. As I said at the beginning, the structured cabling standards also include definitions for communication channels used with different types of fiber cable, so they are included in this standard definition.
Friday, January 8, 2016
Wired Networks
In this unit going to speak about the wired networks and the cables used to build them. Wired communications refers to the transmission of data over cable, some examples are very common, telecommunication networks as telephone network or cable television networks or broadband internet access. The most common used wired media are bare copper wires that can be shielded or unshielded and usually are twisted. Then also coaxial cables and fiber optic cables. But we can also find less common devices, as for example waveguides, used for high power and high frequency applications. Let's start with telephone network with copper pairs that have being used for telecomunications for more than one hundred years and they are are still use as the last mile access technology for most homes and small business, because they are part of a huge interest factor a is very expensive to replace. The design of these telephone networks is very simple and robust: There's one or several copper pairs that connect a home or a business with a street node, where they are connected to a multi-pair cable, usually it's between fifty and five hundred copper pairs and this cable is again connected in another node to another even bigger cable that goes to a local exchange office of the public switched telephone network. Some of these cables can be as big, they can have as much as two thousand and four hundred copper cable pairs. These networks where developed for narrow band voice and were firsts used for data communication employing low bandwidth modems that adapted the digital signals to the voice channel that they had. But in the last twenty years a family of standards called DSL for Digital Subscriber Line have kept growing the bandwidth that can be obtained from a copper wire. They use very clever modulation techniques that squeezed the transmission capacity of the wires and they are getting bandwidth far beyond of what was considered possible some years ago. This technologies also can send these data in parallel with traditional voice calls as they use a different part of the frequency spectrum. That's why if you have a dsl line at home you will need to use a filter to connect the regular phone, because we have to filter out the dsl signal. We are going to see a little bit more in-depth the dsl technologies. The most common dsl technology is adsl for asymmetric digital subscriber line This technology offers different speeds to upload and download data as, we at home, the common users, are far more interested in downloading speed than in uploading things. The fastest versions of dsl are called vdsl for very high-speed digital subscriber line. There are also symmetryc dsl technologies as, for example, sdsl or hdsl, they have the same capacity for uploading and for downloading. The bit rate of consumer dsl services typically ranges from two hundred and fifty six kilobits per second to over one hundred megabytes per second in the direction to the customer, that is called downstream. That depends mainly on the dsl technology employed, a very important parameter is the distance from the node, the line conditions, if the cable is in good condition or if is not so good condition, and the service level implementation. Bit rates of one gigabyte per second have been reached in trials but if you want to instal a DSL line at your home the usual offer you will find will be between ten and one hundred megabits per second depending on the area where you live and how far is your home from the node. And even in some rural areas you would only have access to even lower bandwidths for example one megabit per second or half megabit per second. To end with telephone networks we will mention integrated services for digital networks that is ISDN. ISDN qas a standard type of network created in the late eighties as the future technology for digitalization of telephone networks trying to open them to digital services but as it has very low bandwidth, for example, basic access offers only two 64 kilobytes per second channels to the user, so dsl completely displaced it. ISDN its now used only to connect pbx to the switched telephone network using extended services over plane analog lines. We're going to change now the type of cable, to coaxial cables. Coaxial cable is a type of cable with a central conductor surrounded by a tubular insulating layer that is cover by a cilindrical conducting shield, over the shield it has protecting plastic layer usually called plastic jacket. It is called coaxial because layers share the same axis as you can see in the image. The central conductor and the shield typically made of copper or aluminium. This configuration provides protection of the signal from external electromagnetic interferences ans guarantees a good bandwidth, that's why it is used in transmission line for radio frequency signals. You can find them in feed-lines connecting radio transmitters and receivers to their antenna, in computer network connections in analog and digital baseband distribution and also digital audio studios with S/PIDF bus, or in the distribution of analog and digital radio frequency cable television signals. Most cable tv networks have migrated their networks to digital and they are using their network now to offer broadband internet access to their subscribers using a specially designed cable modems.
In this unit we're going to see the second part of wired networks and the media that supports them. And we're going to start with structured cabling. In the late eighties computer networks were becoming ubiquitous and a United States Industry Association, called Telecommunications Industry Association (TIA) that's and offshoot of the Electronic Industries Alliance (EIA) developed a standard for structured cabling that change completely the computer network business. In nineteen ninety one the first version of TIA/EIA-568 standard was developed and today we are in revision C. It has become so popular that ISO has adapted it and it has become an international standard that's calledISO/IEC 11801. Is not exactly the same but is very, very similar the idea was to create a standard for structured communication cabling in comercial buildings and its connections in a campus environment that separates network hardware characteristics from the cabling characteristics, how do they do that? by guaranteeing a minimum performance of the cabling system up to a given distance. That way the hardware designers can design their hardware without bothering about how cables are going to be because they are going to meet one standard. How do they do that? They define a channel that's formed by the patch cords, the patch pannel, the connectors and the cables that is between one station and the electronic that serve it and they set a minimum performance for this channel. The standard also defines a hierarchical structure in which every desktop station is connected individually to a floor cabinet. And then this floor cabinets are connected to a building cabinet and, if there are several buildings, the building cabinets are connected to a central campus cabinet. The connection between desktop and floor cabinet is done using twisted pair cables, that can be connected to a data network equipment or to regular telephone. So only one type of cable serving voice and data. If we have a voice pbx that is different from the data system. Then, the connection between floor cabinets and the building cabinet is made with fiber optic cables and/or twisted pair cables. Usually you will find a combination of both if cabinets are not too far one from another, so if they are too far we'll only use fiber optics. And the campus backbone is composed of multimode and or single mode fiber cables, depending on the distance and the capacity we want. If there's a traditional pbx, then the links between cabinets can also be completed with multi-pair telephone cables to send the telephone extensions to the different cabinets. There is also a maximum distance for a channel that it's one hundred meters and, as you have to take into account the patch cords in both sides, there is a maximum distance of ninety meter between the cabinet and the desktop connection. To connect the desktop stations we're going to see which cables are used. To connect the desktop stations with the floor cabinet a twisted pair cable with four twisted pairs is used. Every twisted pair consists of two individual copper wires that are twisted one over another, so signal cross-talk is minimized with adjacent pairs. These four pairs are wrapped in an insullation material, usually plastic and in some cases they have a conducting shield per pair (then is called STP for Shield Twisted Pair) or all the pairs have a common shield, then is called Foiled Twisted Pair or FTP. That's done to minimize interference The connector used in both cases has eight wires and is called RJ-45. UTP cables are easier to connect and to install and cables and connectors are less bulky, so most of the installed cable system use UTP cable instead of STP or FTP. Cable and components used, that's it patch cords, patch panels and connectors are assigned a category that depends on its quality and if everything is installed following the standards, that guarantees a minimum channel quality and a minimum bandwidth, for example for the minimum category that's now included in the current standards, that is Cat.3 components, the system guarantees a sixteen MHz bandwidth up to one hundred meters. Now this cables are used only for voice, for telephony. With Cat.5e (for enhance) components guaranteed a one hundred mhz bandwidth up to one hundred meters and that is enough for fast ethernet and for gigabit ethernet. In fact this is the lowest category that is used nowadays for ethernet communications. There are also category six, category six A, that is able to support 10Gbit per second ethernet, category seven and category eight components for example. And each of them is able to work at higher frequencies than the lower category. Other cables that are included in structured cabling, but are also used for wired networks and it's being used by operator, are the fiber optic cables. They are used nowadays in a lot of applications and are made of silica glass, are light, cheap and very durable. Just if you haven't seen any, the diameter of one optical fiber is slightly higher than a human hair. Several fibres are bundled together in a fiber cable that also includes all the components to protect them and to make them stiffer for example, a cover to protect them from external agents. It uses light to transmit information and has a very very high bandwidth and low attenuation, so it can carry a lot of information at very long distances. Another advantage is that it is not influenced by external electromagnetic fields so it is inmune to interferences. Single fiber links in commercial operation today can carry up to one hundred gigabytes up to forty kilometers from the transmitter, So they are very high-capacity systems that go very far. They work by guiding light inside the fibre and to do so they use a variation of the refraction index of the fiber along its diameter, so the light is reflected inside without going out. There are two main types of fibers multi-mode fibers that can use cheaper light sources that are usually based in leds and have less bandwidth and attenuate more the signal, so they are used in shorter distances and single-mode fibers that use more expensive light sources usally based on lasers and have more bandwidth and less attenuation. So they are used for higher capacity systems and longer distances. Fiber cable materials are cheaper than the copper used for twisted pairs, but the associated electronic is much more expensive and the connectorization process is more difficult and so more expensive. So they are used for backbone and in situations where very high bandwidth is needed in one or in several desktop stations or if there are electrical interferences or circumstances that can disrupt other type of communications. As I said at the beginning, the structured cabling standards also include definitions for communication channels used with different types of fiber cable, so they are included in this standard definition.
In this unit we're going to see the second part of wired networks and the media that supports them. And we're going to start with structured cabling. In the late eighties computer networks were becoming ubiquitous and a United States Industry Association, called Telecommunications Industry Association (TIA) that's and offshoot of the Electronic Industries Alliance (EIA) developed a standard for structured cabling that change completely the computer network business. In nineteen ninety one the first version of TIA/EIA-568 standard was developed and today we are in revision C. It has become so popular that ISO has adapted it and it has become an international standard that's calledISO/IEC 11801. Is not exactly the same but is very, very similar the idea was to create a standard for structured communication cabling in comercial buildings and its connections in a campus environment that separates network hardware characteristics from the cabling characteristics, how do they do that? by guaranteeing a minimum performance of the cabling system up to a given distance. That way the hardware designers can design their hardware without bothering about how cables are going to be because they are going to meet one standard. How do they do that? They define a channel that's formed by the patch cords, the patch pannel, the connectors and the cables that is between one station and the electronic that serve it and they set a minimum performance for this channel. The standard also defines a hierarchical structure in which every desktop station is connected individually to a floor cabinet. And then this floor cabinets are connected to a building cabinet and, if there are several buildings, the building cabinets are connected to a central campus cabinet. The connection between desktop and floor cabinet is done using twisted pair cables, that can be connected to a data network equipment or to regular telephone. So only one type of cable serving voice and data. If we have a voice pbx that is different from the data system. Then, the connection between floor cabinets and the building cabinet is made with fiber optic cables and/or twisted pair cables. Usually you will find a combination of both if cabinets are not too far one from another, so if they are too far we'll only use fiber optics. And the campus backbone is composed of multimode and or single mode fiber cables, depending on the distance and the capacity we want. If there's a traditional pbx, then the links between cabinets can also be completed with multi-pair telephone cables to send the telephone extensions to the different cabinets. There is also a maximum distance for a channel that it's one hundred meters and, as you have to take into account the patch cords in both sides, there is a maximum distance of ninety meter between the cabinet and the desktop connection. To connect the desktop stations we're going to see which cables are used. To connect the desktop stations with the floor cabinet a twisted pair cable with four twisted pairs is used. Every twisted pair consists of two individual copper wires that are twisted one over another, so signal cross-talk is minimized with adjacent pairs. These four pairs are wrapped in an insullation material, usually plastic and in some cases they have a conducting shield per pair (then is called STP for Shield Twisted Pair) or all the pairs have a common shield, then is called Foiled Twisted Pair or FTP. That's done to minimize interference The connector used in both cases has eight wires and is called RJ-45. UTP cables are easier to connect and to install and cables and connectors are less bulky, so most of the installed cable system use UTP cable instead of STP or FTP. Cable and components used, that's it patch cords, patch panels and connectors are assigned a category that depends on its quality and if everything is installed following the standards, that guarantees a minimum channel quality and a minimum bandwidth, for example for the minimum category that's now included in the current standards, that is Cat.3 components, the system guarantees a sixteen MHz bandwidth up to one hundred meters. Now this cables are used only for voice, for telephony. With Cat.5e (for enhance) components guaranteed a one hundred mhz bandwidth up to one hundred meters and that is enough for fast ethernet and for gigabit ethernet. In fact this is the lowest category that is used nowadays for ethernet communications. There are also category six, category six A, that is able to support 10Gbit per second ethernet, category seven and category eight components for example. And each of them is able to work at higher frequencies than the lower category. Other cables that are included in structured cabling, but are also used for wired networks and it's being used by operator, are the fiber optic cables. They are used nowadays in a lot of applications and are made of silica glass, are light, cheap and very durable. Just if you haven't seen any, the diameter of one optical fiber is slightly higher than a human hair. Several fibres are bundled together in a fiber cable that also includes all the components to protect them and to make them stiffer for example, a cover to protect them from external agents. It uses light to transmit information and has a very very high bandwidth and low attenuation, so it can carry a lot of information at very long distances. Another advantage is that it is not influenced by external electromagnetic fields so it is inmune to interferences. Single fiber links in commercial operation today can carry up to one hundred gigabytes up to forty kilometers from the transmitter, So they are very high-capacity systems that go very far. They work by guiding light inside the fibre and to do so they use a variation of the refraction index of the fiber along its diameter, so the light is reflected inside without going out. There are two main types of fibers multi-mode fibers that can use cheaper light sources that are usually based in leds and have less bandwidth and attenuate more the signal, so they are used in shorter distances and single-mode fibers that use more expensive light sources usally based on lasers and have more bandwidth and less attenuation. So they are used for higher capacity systems and longer distances. Fiber cable materials are cheaper than the copper used for twisted pairs, but the associated electronic is much more expensive and the connectorization process is more difficult and so more expensive. So they are used for backbone and in situations where very high bandwidth is needed in one or in several desktop stations or if there are electrical interferences or circumstances that can disrupt other type of communications. As I said at the beginning, the structured cabling standards also include definitions for communication channels used with different types of fiber cable, so they are included in this standard definition.
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