Cables_ Cables and More Cables

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					Cables, Cables and More Cables
How does a T1 Line Work?

   Most of us are familiar with a normal
    business or residential line from the phone
    company. A normal phone line like this is
    delivered on a pair of copper wires that
    transmit your voice as an analog signal.
    When you use a normal modem on a line like
    this, it can transmit data at perhaps 30
    kilobits per second (30,000 bits per second).
How does a T1 Line Work?

      If your office has a T1 line, it means that the
     phone company has brought a fiber optic line
     into your office that can carry data at a rate of
               1.544 megabits per second.
How Fast is Fast?

   A large company needs something more than a T1 line. The
    following list shows some of the common line designations:
       DS0 - 64 kilobits per second
       ISDN - Two DS0 lines plus signaling (16 kilobytes per second), or 128 kilobits per
       T1 - 1.544 megabits per second (24 DS0 lines)
       T3 - 43.232 megabits per second (28 T1s)
       OC3 - 155 megabits per second (84 T1s)
       OC12 - 622 megabits per second (4 OC3s)
       OC48 - 2.5 gigabits per seconds (4 OC12s)
       OC192 - 9.6 gigabits per second (4 OC48s)
Why the difference in speed with my
cable modem?
   You have encountered one of the fundamental problems with cable
    modems. Each cable modem is part of a loop that begins at the cable
    company's central office, goes through a certain neighborhood or group of
    neighborhoods, and comes back to the central office. When a cable
    company offers Internet access over the cable, Internet information can use
    the same cables because the cable modem system puts information on
    separate channels:
       Downstream data -- data sent from the Internet to an individual computer -- into a 6 MHz
        channel. On the cable, the data looks just like a TV channel. So Internet downstream data
        takes up the same amount of cable space as any single channel of programming.
       Upstream data -- information sent from an individual back to the Internet -- requires even less
        of the cable's bandwidth, just 2 MHz, since the assumption is that most people download far
        more information than they upload.
Cable Modems
   As more people in your neighborhood subscribe to the cable modem, the
    amount of bandwidth available per user decreases. This means that if you
    and a lot of your neighbors all get online at the same time, then you will
    notice a significant performance hit. The good news is that this particular
    performance issue can be resolved by the cable company adding a new
    channel and splitting the base of users. Most cable companies monitor
    performance regularly and add another channel when the bandwidth per
    user hits a certain point.
   As a user, you can observe when the speed of your connection is sluggish
    and try to avoid that particular time of day. Often, just by changing the time
    you are online, you can gain substantial improvement in speed. After dinner
    is traditionally the slowest average connection speed. Why?
DSL – Digital Subscriber Line
   Here are some advantages of DSL:          But there are disadvantages:
      You can leave your Internet               A DSL connection works better
       connection open and still use the          when you are closer to the
       phone line for voice calls.                provider's central office.
      The speed is much higher than a           The farther away you get from the
       regular modem                              central office, the weaker the
      DSL doesn't necessarily require            signal becomes.
       new wiring; it can use the phone          The connection is faster for
       line you already have.                     receiving data than it is for sending
      The company that offers DSL will           data over the Internet.
       usually provide the modem as part         The service is not available
       of the installation.                       everywhere
   The copper wires have lots of room for carrying more than your phone conversations
    -- they are capable of handling a much greater bandwidth, or range of frequencies,
    than that demanded for voice. DSL exploits this "extra capacity" to carry information
    on the wire without disturbing the line's ability to carry conversations. The entire plan
    is based on matching particular frequencies to specific tasks.
   The use of such a small portion of the wire's total bandwidth is historical -- remember
    that the telephone system has been in place, using a pair of copper wires to each
    home, for about a century. By limiting the frequencies carried over the lines, the
    telephone system can pack lots of wires into a very small space without worrying
    about interference between lines. Modern equipment that sends digital rather than
    analog data can safely use much more of the telephone line's capacity. DSL does just
Networking Cables

   Category 5 cable, commonly known as Cat 5 or
    "Cable and Telephone", is a twisted pair cable type
    designed for high signal integrity. Many such cables
    are unshielded but some are shielded. Category 5
    has been superseded by the Category 5e
    specification. This type of cable is often used in
    structured cabling for computer networks such as
    Ethernet, and is also used to carry many other
    signals such as basic voice services, token ring, and
    ATM (at up to 155 Mbit/s, over short distances).
Ethernet Cable – RJ45 Connector
Networking Cables - Fiber

   An optical fiber (or fibre) is a glass or plastic fiber
    designed to guide light along its length. Optical
    fibers are widely used in fiber-optic communication,
    which permits transmission over longer distances
    and at higher data rates than other forms of
    communications. Fibers are used instead of metal
    wires because signals travel along them with less
    loss, and they are immune to electromagnetic
    interference. Optical fibers are also used to form
    sensors, and in a variety of other applications.
Fiber Optic

   Joining lengths of optical
    fiber is more complex than
    joining electrical wire or
    cable. The ends of the
    fibers must be carefully
    cleaved, and then spliced
    together either mechanically
    or by fusing them together
    with an electric arc. Special
    connectors are used to
    make removable
Fiber Optic – LC Connector
Fiber Optic – MT-RJ Connector,85,772&mid=4983
Crossover Cables

   This slideshow shows how to properly construct a
    Crossover network cable. This cable can be used to
    directly connect two computers to each other without
    the use of a hub or switch. The ends on a crossover
    cable are different from each other, whereas a
    normal 'straight through' cable has identical ends.
    Their uses are shown in the following diagrams.
The Crossover Difference

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