# 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
second
   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
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
DSL
   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
that.
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
connections.
Fiber Optic – LC Connector
Fiber Optic – MT-RJ Connector

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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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 views: 5 posted: 2/17/2012 language: pages: 18