Understanding the network.pdf - Back to Home

Coaxial cable has a single solid copper core and a braided or foil shield. The core and
the shield are separated by a plastic insulator. Thin coaxial cable is used with
connectors known as British Naval Connectors (BNCs). Thick coaxial cable is used
with coax or vampire taps. Installing taps requires that the cable have a small hole
drilled into the casing and through the shielding. Then, the tap is inserted in the hole
and tightened down so the tap pierces firmly into the copper core. Coaxial cable has
very desirable transmission characteristics.
Twisted-pair cable is by far the most common data transmission medium.A
twisted-pair cable is two solid copper wire strands of either 22 or 24 AWG, wound
around each other in a double helix, similar to a DNA strand. As with coaxial cable
transmission, signals are sent using DC voltage. Then, the twisted pairs are put
inside a larger casing to finish the cable. Twisted-pair cables range in size from a
single pair to 1,000 pairs. The amount of twists, known as the pitch, is measured in
pitch per foot. The cable pitch reduces the amount of crosstalk (electrical
interference) between signals sent across the cable. A cable's pitch, along with the
medium's signal latency, resistance (its diameter), and physical strength,
determines its grade. Under the cable grading system, there are service levels
(transmission speeds) associated with different grades. Most enterprises use cable
up to Category 5. Table 1.1 lists the common cable types and their application.
NOTE
AWG refers to the American Wire Gauge standard for thickness. The higher the AWG,
the smaller the diameter of the wire.
Table 1.1. Common Twisted-Pair Cable Types
Category 1 Voice or low-speed data transfers up to 56Kbps.
Category 2 Data transfers up to 1Mbps.
Category 3 Data transfers up to 16Mbps.
Category 4 Data transfers up to 20Mbps.
Category 5 Data transfers up to 100Mbps.
Voice Grade Cable (VGC) is Category 3 and is used for telephone and low-speed
data transmission. Data Grade Cable (DGC) is Category 5 and is used for high-speed
data transmission. Twisted-pair cable has limited bandwidth, high attenuation and
is susceptible to electronic interference. By using a signal repeater, the bandwidth
and attenuation can be addressed.