On a local area network (LAN), network devices will traditionally connect to each other using some type of cabling. Even on LANs that
has a wireless segments, the access points will be connected to the core network using a physical network connection. Over the years, different
types of networks have used a number of different types of cables. As layer 2 technologies have developed, so has network cabling.
All cables used in the computer networking industry, past and present, can be categorized in three distinct groups: coaxial (coax),
twisted pair, and fiber-optic.
Coaxial (coax) cable has been around for many years and is very commonly used in the video industry. Coax was also used on early networks,
but is no longer being widely implemented for network communication. Coax is a very sturdy cable and contains a central conductor wire
surrounded by an insulating material, which in turn is surrounded by a braided metal shield. There are few variations of this cable some with
thicker copper cores than others. The differences in the type of coax that you use may allow you to use them in different capacities, such as
in running longer distance cabling. Coax wire was used on the original Ethernet networks implemented with a Bus Topology. Computer networks that use
coax cable will use a thicker type of coax known as RG-6 (75 Ohms). For television and other video transmissions, RG-59 is was historically
used. It is now more common to find both networking and video applications to use RG-6.
Coaxial cable shields data transmissions from electro-magnetic interference (EMI). Electrical devices produce EMI. When a metal wire
encounters these magnetic fields, electrical current is generated along the wire. This electric current on your network wire will cause major issues. The outer mesh layer of a coaxial cable shields the
center from the unwanted interference. Even though the wire is protected, you want to make sure you keep your wires away from electrical devices.
Twisted Pair Cable
By far, the most common type of cabling used on modern networks today consists of twisted pair cabling. Twisted pair cabling is a type of cabling,
that contains individual stands of copper cables bundled together into a common jacket. Individual pairs of cable are twisted together. You will find two types of twisted-pair cabling on modern
networks: shielded twisted pair (STP) and unshielded twisted pair (UTP). The primary reason for twisted pair cabling is to reduce interference, also
known as crosstalk. As mentioned in the Coaxial section, cabling is susceptible to magnetic interference. The twists in UTP and STP cables is used
to mitigate the crosstalk problem. The more twists, the less crosstalk.
STP, or Shielded twisted pair, as its name implies, consists of twisted pairs of wires surrounded by shielding to protect them from EMI. STP is not generally
implemented on networks unless it is absolutely necessary. It is more costly than UTP cabling and in many cases, to mitigate EMI, you simply just need to
run the UTP cabling away from electrical devices that produce magnetic interference. UTP consists of twisted pairs of wires surrounded by a
plastic jacket. This jacket does not provide any protection from EMI, so as mentioned earlier, you must keep the cable away from electrical interference.
UTP cabling has a number of variations, such as the number of twists per foot. The more twists, the faster you can move data on the wire. The
cabling industry has developed a variety of grades called category (CAT) ratings. CAT ratings are rated in megahertz (MHz)
|Category||Max Frequency||Max Bandwidth|
|CAT 1||1 MHz|| |
|CAT 2||4 MHz||4 Mbps|
|CAT 3||16 MHz||16 Mbs|
|CAT 4||20 MHz||20 Mbs|
|CAT 5||100 MHz||100 Mbs|
|CAT 5e||100 MHz||1 Gbs|
|CAT 6||250 MHz||10 Gbs|
Fiber Optic Cable
Fiber optic cable has one main advantage over copper cabling. It transmits light rather than electricity. Therefore, fiber optic cabling is not
susceptible to EMI. While a copper cable is unable to carry a signal more than a few hundred meters, fiber optic cabling can be run for distances up to
tens of kilometers.
A fiber optic cable generally has four components: the core (glass fiber), the cladding (reflects light down the fiber), buffer material for
strength, and the insulating jacket for protection. Fiber optic cabling is manufactured with different diameters of core and cladding. The most
common fiber optic cable size is 62.5/125 μm. Fiber optic cable will either be multimode or single mode cable. Multimode fiber is used with LEDs to
transmit data, while singlemode fiber is used with Lasers. Singlemode cable is generally more expensive and can be used for longer distances when compared
to multimode fiber cable.
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