Transmisson media
TRANSMISSION MEDIA
The means through which data is transformed from one place to
another is called transmission or communication media. There are two categories
of transmission media used in computer communications.
·
BOUNDED/GUIDED MEDIA
·
UNBOUNDED/UNGUIDED MEDIA
1. BOUNDED MEDIA:
Bounded media are the physical links through which signals are
confined to narrow path. These are also called guide media. Bounded media are
made up o a external conductor (Usually Copper) bounded by jacket material.
Bounded media are great for LABS because they offer high speed, good security
and low cast. However, some time they cannot be used due distance
communication. Three common types of bounded media are used of the data
transmission. These are
·
Coaxial Cable
·
Twisted Pairs Cable
·
Fiber Optics Cable
COAXIAL CABLE:
Coaxial cable is very common & widely used commutation media.
For example TV wire is usually coaxial.
Coaxial cable gets its name because it contains two conductors
that are parallel to each other. The center conductor in the cable is usually
copper. The copper can be either a solid wire or stranded martial.
Outside this central Conductor is a non-conductive material. It is
usually white, plastic material used to separate the inner Conductor form the
outer Conductor. The other Conductor is a fine mesh made from Copper. It is
used to help shield the cable form EMI.
Outside the copper mesh is the final protective cover. (as shown
in Fig)
The actual data travels through the center conductor in the cable.
EMI interference is caught by outer copper mesh. There are different types of
coaxial cable vary by gauge & impedance.
Gauge is the measure of the cable thickness. It is measured by the
Radio grade measurement, or RG number. The high the RG number, the thinner the
central conductor core, the lower the number the thicker the core.
Here the most common coaxial standards.
·
50-Ohm RG-7 or RG-11 :
used with thick Ethernet.
·
50-Ohm RG-58 : used with
thin Ethernet
·
75-Ohm RG-59 : used with
cable television
·
93-Ohm RG-62 : used with
ARCNET.
CHARACTERISTICS OF COAXIAL CABLE
·
Low cost
·
Easy to install
·
Up to 10Mbps capacity
·
Medium immunity form EMI
·
Medium of attenuation
ADVANTAGES COAXIAL CABLE
·
Inexpensive
·
Easy to wire
·
Easy to expand
·
Moderate level of EMI
immunity
DISADVANTAGE COAXIAL CABLE
·
Single cable failure can
take down an entire network
Twisted Pair Cable
The most popular network cabling is Twisted pair. It is light
weight, easy to install, inexpensive and support many different types of
network. It also supports the speed of 100 mps.Twisted pair cabling is made of pairs of solid or stranded copper
twisted along each other. The twists are done to reduce vulnerably to EMI and
cross talk. The number of pairs in the cable depends on the type. The copper
core is usually 22-AWG or 24-AWG, as measured on the American wire gauge standard. There are two types
of twisted pairs cabling
1. Unshielded twisted pair (UTP)
2. Shielded twisted pair (STP
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