Transmission Media -Cont

Coaxial Cable Standards Different  coaxial  cable  designs  are  categorized  by  their  Radio  government  ( RG ) ratings Each RG number denotes a unique set of physical specifications, including -the wire gauge of inner conductor - the thickness and type of inner insulator -Construction of the shield -Size and type of outer casing Each cable defined by RG rating is adapted for a specialized function:

RG-8 RG-9

-Used in Thick Ethernet -Used in Thick Ethernet

RG-11 -Used in Thick Ethernet RG-58 -Used in Thin Ethernet RG-59 -Used for TV    Coaxial Cable Connectors o    Over  the  years,  a  no.  of  connectors  have  been  designed  for  use  with  coaxial cable o    Most common of the connectors is called "BARREL connector" because of its shape o    Of the barrel connectors, the most popular is the Bayonet Network Connector (BNC) o    BNC connector pushes on and locks into place with half turn o    Other  types  of  barrel  connectors  either  screw  together  and  so  require  more effort to install or push on w/o locking which is less secure o    Coaxial cables are familiar in Cable TV and VCR hookups that employ both threaded and alip on style o    Two other commonly used connectors are T-connectors and Terminators A T-connector (used in Thin Ethernet) allows a secondary cable or cables to branch off from a main line Terminators are required for bus topologies where one main cable acts as a backbone  with  branches  to  several  devices  but  does  not  itself  terminate  in  a device If main cable is left un terminated, any signal tx over the line echoes back and interferes with the original signal A terminated absorbs the wave at the end and eliminates this echo ™   Optical Fiber o    Until this point we have discussed conductive (metal) cables that transmit signals in the form of current Optical fiber is made of glass or plastic It transmits signals in the form of light    The Nature of Light The speed of light -300,000 Km/sec in a vacuum -Depends on the density of the medium through which it is traveling -The higher the density, the slower the speed •     Refraction o    Light travels in a straight line as long as it is moving through a single uniform structure o     If a ray of light traveling through one substance enters another (more or less dense)   substance,   its   speed   changes   abruptly   causing   the   ray   to   change direction o    This phenomenon is called Refraction