Transcript document
Hardware Concepts
Chapter 4
Contents
• Explain the different types of network topology
• Describe the different types of network cabling
• Describe and distinguish between the 802.2,
802.3, 802.5, and 802.11 IEEE networking
standards
Topology
Topology
• A topology describes how computers connect to
each other
Types of Topologies
• Bus
– All computers connect via a main line, called a bus
cable
• Ring
– All computers attach to a central ring of cable
• Star
– All computers connect to a central wiring point,
usually a hub
• Mesh
– Each computer has a dedicated line to every other
computer
Types of Topologies
Network Technologies
• A network technology is a practical application
of a topology to get data from one computer or
network to another
– Ethernet
– Token Ring
– FDDI-(Fiber Distributed Data Interface) is a standard
for data transmission on fiber optic lines in a local
area network (LAN) that can extend in range up to 200
km
Bus Topology
• Ethernet was the first network technology that
used the bus topology
• Each computer on the network is connected to
the single cable
Bus Topology
• If there is a break in the cable, the entire network
would stop functioning
– It has no fault tolerance to survive a problem
Star Topology
• Each computer is connected to a central device
such as a hub
– If a cable breaks only the one computer is affected
Star Bus Topology
• A star bus topology is a hybrid topology
– Uses a physical star topology
– Uses a logical bus topology
– Most common topology used today
Token Ring Topology
• Token ring uses a star ring topology
– Uses a physical star topology
– Uses a logical ring topology
– Declining in popularity
Cabling
Coax
• Coaxial cable (or coax)
contains a central
conductor wire,
surrounded by an
insulating material,
which in turn is
surrounded by a
braided metal shield
EMI
• Electro-magnetic
interference (EMI)
is caused by lights,
fans, copy machines,
and other devices
• EMI corrupts the
signal flowing
through the cable
• The braided shield
helps to reduce the
effects of EMI
Types of Coax Cable
• The Ohm rating is a measure of resistance in the
cable and differentiates different types of coaxial
cable
• RG-8, RG-62, and RG-58 are used in computer
networks
RG-8
• RG-8 cable is also called Thick Ethernet
– Oldest type of coax still in use
– Rated at 50 ohms
– Yellow or orange/brown color
RG-62
• RG-62 cable is never
installed in networks
today
– Was used with ARCnet
RG-58
• RG-58 is also called
Thin Ethernet
– Still in widespread
use today
Twisted Pair
• Shielded Twisted Pair (STP) and Unshielded
Twisted Pair (UTP) are the most common types
of cabling used today
– Composed of multiple pairs of wires twisted together
to reduce interference from adjacent wires, called
crosstalk
Shielded Twisted Pair (STP)
• Twisted pairs of wires surrounded by shielding
to protect them from EMI
– Only used in older Token Ring networks
Unshielded Twisted Pair (UTP)
• Most common type of cabling used in networks
– Twisted pairs of wires surrounded by a plastic jacket
– Inexpensive and flexible
CAT Ratings
• Twisted pair cabling varies by things like the
number of twists per foot
• Cables are rated in categories or CAT ratings (or
levels)
CAT Ratings
CAT Rating
Bandwidth
Typical Throughput in Networks
CAT 1
<1 MHz
Analog phone lines – not data
CAT 2
4 MHz
Speeds up to 4 Mbps
CAT 3
16 MHz
Speeds up to 16 Mbps
CAT 4
20 MHz
Speeds up to 20 Mbps
CAT 5
100 MHz
Speeds up to 100 Mbps
CAT 5e
100 MHz
Speeds up to 1000 Mbps
CAT 6
200-250 MHz
Speeds up to 10000 Mbps
CAT Usage
• Most new installations use CAT 5e cable since it
is cheaper than CAT 6 cable
CAT level
CAT level
Fiber Optic
• Fiber optic cabling
transmits light rather than
electricity
– Immune to EMI
– Very long distances
– Consists of the fiber,
cladding, and insulating
jacket
– Defined by fiber and
cladding measurements
– Most common is 62.5/125
µm
– Fiber generally requires
two cables
Light Sources
• Fiber optic cables use two possible light
sources
– Light Emitting Diodes (LEDs) – called multimode
– Lasers – called single-mode
• Supports faster speeds and longer lengths
Networking Industry Standards
IEEE
• Institute of Electrical and Electronic Engineers
(IEEE) defines industry-wide standards
• Organized the 802 committee in February of
1980 to define networking standards
– Split up into smaller subcommittees
IEEE Subcommittees
IEEE 802
LAN/MAN Overview & Architecture
IEEE 802.2
Logical Link Control (LLC)
IEEE 802.3
CSMA/CD access method (Ethernet)
IEEE 802.3ae
10 Gigabit Ethernet
IEEE 802.5
Token Ring access method and Physical layer
specifications
IEEE 802.8
Fiber Optic
IEEE 802.11
Wireless LAN Medium Access Control (MAC) and
Physical layer specifications
There are more subcommittees than listed in this table.