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Chapter 6 Local-Area Networks
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Fire Controlman Volume 06-Digital Communications
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LOCAL-AREA  NETWORK  HARDWARE The  basic  hardware  components  of  a  LAN  are cables,  network  interface  cards,  network  servers, peripherals, and workstations. These components are covered in the material that follows. CABLES Several  types  of  cables  can  be  used  in  LAN applications. The  selection  of  the  type  of  cable depends on several factors, such as maximum length of a single cable run, security requirements, and the capacity and speed of the system. Twisted-Pair Cable The twisted-pair cable is easy to install and costs little  on  a  per-foot  basis.  In  some  cases,  existing telephone   cable   may   be   used.   Its   disadvantages include limitations in capacity and speed. It is also susceptible   to   electrical   interference   unless   it   is shielded. Shielded Twisted-Pair Cable The shielded twisted-pair cable is encased in an RFI shield. The stranded wire used as a conductor is manufactured  with  greater  precision  and  is  capable  of greater  data  transmission  rates  and  longer  cable  runs. Coaxial Cable Coaxial  cable  networks  have  gained  in  popularity because  of  their  use  in  cable  television.  The quantities  of  cable  and  connectors  produced  for  cable television  have  greatly  reduced  the  prices  of  these components for network users. Coaxial cable comes in various thicknesses and is designated by a number: RG-11, RG-58, RG-59, RG-62, and so forth. You can use  either  baseband  or  broadband  transmission methods with coaxial cable. Baseband coaxial systems  transmit digital signals unchanged  over  a  single  channel  and  have  several advantages.  They  are  inexpensive,  easy  to  install,  and have  low  maintenance.  They  also  allow  very  high data  transmission  rates.  One  disadvantage  is  that  they are limited to transmitting digital signals only. In contrast, broadband coaxial systems  require the digital signal to be converted to an analog signal before  transmission  and  then  back  to  digital  by modem at the receiving device. Broadband systems support  data,  voice,  and  video  signals  that  may  be transmitted    simultaneously. Disadvantages   of broadband systems are their higher installation costs and  complex  maintenance. Fiber-Optic Cable Fiber-optic  cable  is  the  best  choice  if  a  secure network  is  needed.  Because  the  cable  transmits  light, the transmissions are immune to interference caused by  electrical  or  electronic  devices.  Also,  if  your network will run through an area of heavy industrial activity or a work place with strong radio frequency interference,  fiber-optic  cable  is  the  most  appropriate choice. Other advantages of the fiber-optic cable are that it lasts longer than other types of cable and can carry many more channels. Its disadvantages include its high price, poor connectivity, and low flexibility. NETWORK  INTERFACE  CARD To  attach  personal  computers  to  the  LAN,  you must connect a network interface card (NIC) to each PC and attach the network cable to the NIC. The NIC is  nothing  more  than  a  circuit  board  that  normally plugs  directly  into  one  of  the  expansion  slots  inside  a PC. Sometimes, the NIC comes as a separate unit. In this case, you plug it into the back of the PC. Most NICs  have  their  own  built-in  microprocessor(s) designed  to  take  care  of  network  communications. This   relieves   the   PC’s   main   processor   of   this responsibility.  The  type  of  cable  used  on  the  network is determined by the type of LAN to be installed. NETWORK  SERVERS Your  understanding  the  concept  of  a  server  is important   to   understanding   how   LANs   work.   A server is a combination of hardware and software that is used to manage the shared resources of the network. The hardware may be a PC or a computer designed 6-2






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