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The Concept If its local or wide area network you need, let us survey and quote for the job, we specify equipment to suit your building and your business requirement, from just two computers to a large system with multiple servers, hubs and workstations, using 10base-T (Cat 5/6), 10base-2 or 10base-FL, for the network links we can cover large buildings and establish communications between buildings in harsh environments. As a forward looking business we can install all the components of a network, from the cabling through to the final software set up for each user. We can update or upgrade existing systems with extra desktop terminals, hardware such as routers, networked printers and any software to improve your user's efficiency, we specialise in Microsoft NT4, NT Server and Back Office with Exchange Server etc. If necessary we have consultants who work with Unix and Novell operating systems. Many parts of the electronic fire and security market are experiencing rapid technological change, particularly those relating to Telecommunications and Information Technology, this could require a structured cable system which is the infrastructure of any communication, computer and information network. Copper and/or fibre cables are linked together to carry all of the voice, data, video and Internet traffic throughout a building. Primarily hidden within building walls and ceilings, this
cable infrastructure is uniquely designed, or structured, to maximise data rates and
optimise network efficiency. No single investment in technology will last longer than the
cable system - the cable infrastructure is the foundation on which all other technologies
will run. Networks can include options such as, Building
Management Systems (BMS) which create and maintain energy-efficient, comfort-controlled
environments for all types of premises, including those in the commercial, industrial,
healthcare and leisure sectors. The structured cabling concept is to cable a building so that any voice or data service in the building can be accessed or is accessible from every communication outlet. This is made possible by having each service distributed throughout the building by means of a standard structured wiring cable. A standard structured wiring cable allows any moving of personnel, or addition of services to be carried out without the need for costly rewiring. The only possible way to achieve this is to cable the building with many more communication outlets than will be used at any one time. This requires installation of outlets at regular distances around the building to give coverage to every area where a voice or data service will be required. When a cabling system is installed in this way it allows any person to move to any location within the building and still access every service by the simple means of patching. Recent technological advances have meant that very high quality cabling; increasing the speed and distance of the cable runs; is now available cheaper than ever before, so companies can install many more communication outlets, over a much wider area. As a single cable type is now being used to run many different services an easy method of cross connection has been developed to allow the system to be effectively managed. The cross connections are achieved by presenting each port of the main frame on a panel and each floor data point on a separate panel. Cross connections are then made by simply plugging a short lead into the relevant ports on the separate panels. This method of cross connection is known as modular patching. Modular patching's great advantage is its flexibility, any moves changes or additions in either personnel or services can easily be accommodated simply by patching the relevant ports and expansion is easily coped with by simply adding panels. The Standards Category 3 UTP specifications can handle transmission rates up to 10 Mbps, which means that they can be used for Ethernet LAN's, voice traffic or 4 Mbps Token Rings. Category 4 UTP products handle transmission rates up to 16 Mbps, making them suitable for 16 Mbps Token Rings and other low speed networks. Category 5 UTP products can handle transmission rates up to 100 Mbps, making them suitable for high speed networks. Note that categories 1 and 2 are excluded as they are not recommended for data applications.. Structured Cabling Design There are three types of cable that can be used in structured cabling design, UTP, FTP and Fibre. UTP is the most widely used cable in the UK and is used as the primary media for floor distribution. A UTP backbone is often installed for voice services. FTP is used in applications where noise is deemed to be a problem. When installed correctly it can allow the use of structured cabling where previously the environment was too harsh. Fibre is predominantly used as a backbone media for data services, its high speed and band width being ideal for this purpose. Connectors Horizontal cabling is terminated at the outlet or at a patch panel by 'punching down' on to IDC (insulation displacement connection) blocks at the back of the socket. IDC blocks have traditionally eight contact points (to accommodate four pairs or eight cores.) IDC allows quick efficient and cost effective termination of cables. The other major connection technique used primarily in connecting patch panels the RJ45 plug. This is an eight pin plug that is crimped down and around a four pair patch cable. There are two major pin/pair assignments; T568A and T568B, both are detailed in EIA/TIA 568 and IS 11801. Installation Practices UTP provides an infrastructure platform across which most products can be supported. In layout an UTP Cabling System has a star wired configuration, all wall outlets are fed back to a central patch panel. Patch leads are used to connect to services. Ideally buildings would be flood wired with UTP cabling when constructed. For the cable connected between the cabinet and the outlet the accepted maximum run length is 100m which gives a typical installed length of 90m all lowing for patching. The cable consists of four twisted pairs with solid core wire for the installed section and stranded wire for the patch leads. There are now 5 categories for UTP cabling with the top three (3, 4 and 5) being used for data applications. Category 5 cabling supports 100 Megabits per second (Mbps) data and is the cable to install to future proof the system. Advantages of UTP Cabling
The Advantages of FTP Cabling
FTP can offer a high level of protection with out significant additional cost. The installation of FTP cable does minimise the sensitivity to routing (Proximity to EMI sources) but adds complexity in terms of the quality of connections and grounding (Earthing). The key to utilising FTP is to make the system as compatible as possible with standard UTP design, installation and maintenance. This will minimise the impact of this media on system availability. For example using 100 ohm nominal impedance cable. This matches the impedance of UTP so that any equipment designed for UTP will work well on FTP wiring. UTP equipment is more widespread so it should be less expensive. This allows for mixing of media within a building; for example the use of FTP for factory runs and UTP for office runs within the same building. Grounding Incorrect grounding of cable shields can result in worse performance than would be experienced from the use of an equivalent grade of UTP. Therefore it is imperative that ground points are properly chosen initially and maintained. Electrical Parameters Near End Crosstalk (NEXT) When current flows in a wire, an electromagnetic field is created which can interfere with signals on adjacent wires. As frequency increases, this effect becomes stronger. Each pair is twisted because this allows opposing fields in the wire pair to cancel each other out. The tighter the twist, the more effective the cancellation, and the higher the data rate supported by the cable. Maintaining the twist ratio is the single most important factor in any successful UTP installation. In LAN's, NEXT occurs when a strong signal on one pair of wires is picked up by an adjacent pair of wires. NEXT is the proportion of the transmitted signal that is electromagnetically coupled back into the received signal. The receiver may not be able to distinguish between the real received signal and the cross talk noise. It is extremely important to measure NEXT from both ends of the cable or link under test as NEXT is specific to each end of the link, and it is normal to get significantly different results at each end. All standards which include NEXT measurements require this. Note that low NEXT is a high number (e.g. 45 dB) High NEXT (undesirable) is a low number (20 dB) Attenuation Attenuation, is the loss of a signal in a cable or link, is measured in dB's and is dependant upon length and frequency. When data is transmitted through a cable, the signal weakens. This is due to the size and grade of the copper used, the insulation materials and other design factors. Cat. 5 cables are better designed and use superior materials than their Cat. 3 equivalents. Consequently their attenuation figures are far better. Attenuation and therefore the length over which the cable can be run is a major factor in general LAN design IS 11801 recognises this and sets out the maximum lengths for specific cables at specific frequencies. Attenuation To Crosstalk Ratio (ACR) Due to the effects of attenuation,signals are at their weakest at the receiver end of the link. But it is also where NEXT is the strongest. Signals that survive attenuation must not get lost due to the effects of NEXT. In UTP networks attenuation determines the strength of the received signal, while the noise is primarily the NEXT from the stations own transmitter. Attenuation - to - crosstalk - ratio (ACR) is the difference between the crosstalk loss and the attenuation for the pair in the link under test. ACR is a figure of merit for the cable, in essence it is a measure of how much 'overhead' you have between the size of the signal at the receiver and the size of the crosstalk noise. Thus the greater the ACR the better. ACR is specified in the ISO and IEEE standards but not in EIA/TIA 568A. Wire Map Wire Map is used to identify installation wiring errors. For each of the eight conductors in the cable, wire map indicates:
Characteristic Impedance The Characteristic Impedance of a system is a measure of its balance, expressed in Ohms. Standard structured UTP or FTP cabling systems have a nominal impedance of 100 ohms. Cable associated hardware and active equipment also have defined impedance values and it is of paramount importance that they all match. When mismatches are present reflections, increased losses and high data errors can often occur with potentially devastating effects on the overall network. Cat. 5 standards define impedance values, for cable and hardware and it is not permissible for even one point to be outside of this range. Noise Noise is undesirable electrical activity in a conductor, in LAN environments this may typically include AC transmission lines, fluorescent light fixtures, industrial equipment and lifts. Noise problems also occur when other wire pairs in the same sheath are tested for non - LAN applications. Often noise problems can be corrected by moving the cable away from the source or removing the source. The most common types of noise are electromagnetic interference (EMI) and radio frequency interference (RFI) . EMI is characterised by lower frequencies and higher amplitudes, and comes from sources such as motors (lifts), AC power lines and fluorescent light fixtures. RFI is characterised by higher frequencies, lower amplitudes and comes from sources such as cellular phones, radio, TV and high frequency switching power supplies. Capacitance Capacitance is a measure of the total amount of charge stored between two electrical components. High values have a detrimental effect on communication signals, especially at high frequencies. Bit Rate vs Frequency There has been endless confusion on what defines the speed of a network. There is a difference between Megahertz (MHz) and Megabits per second (Mbps). A bit is the smallest piece of information that can be processed by a computer, it can take up to eight bits to make up one character. MHz is a measure of a signal voltages frequency in a thousand cycles per second, one Hz is one complete cycle. While higher frequencies can mean faster networks a truer measurement of communication speed is bit rate or Mbps. Bit rate does not necessarily equal frequency, although for some systems they match closely.
In summary the EIA/TIA Standards are as follows: EIA/TIA 568A - 1994 - Commercial Buildings Telecommunications Wiring Standard. EIA/TIA TSB 36 - 1991 - Additional Specifications for UTP Cables (defines Cat. 3, 4 and 5) EIA/TIA TSB 40A - 1994 - Additional Specifications for UTP Connecting Hardware (Cat. 3, 4 and 5 connecting hardware) EIA/TIA TSB - 67 - Link Performance.
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