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Transcript
Networks & Communications
Introduction
Overview
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Network Topology
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Bus Network
Ring Network
Star Network
Tree Network
Mesh Network
Network Characteristics
Network Applications
The Internet
Bus Network
Bus Network
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A bus network is an arrangement in a local area network (LAN) in
which each node (workstation or other device) is connected to a
main cable or link called the bus. The illustration shows a bus
network with five nodes. Each node is shown as a sphere, the bus
appears as a heavy horizontal line, and connections to the bus
appear as vertical lines.
A bus network is simple and reliable. If one node fails to operate, all
the rest can still communicate with each other. For a major
disruption to take place, the bus itself must be broken somewhere.
Bus networks are easy to expand. Additional nodes can be added
anywhere along the bus.
There are several limitations to the bus network topology. The
length of the bus is limited by cable loss. A bus network may not
work well if the nodes are located at scattered points that do not lie
near a common line.
Ring Network
Ring Network
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A ring network is a local area network (LAN) in which the nodes
(workstations or other devices) are connected in a closed loop
configuration. Adjacent pairs of nodes are directly connected. Other
pairs of nodes are indirectly connected, the data passing through
one or more intermediate nodes. The illustration shows a ring
network with five nodes. Each node is shown as a sphere, and
connections are shown as straight lines. The connections can consist
of wired or wireless links.
A break in the cable of a ring network may result in degraded data
speed between pairs of workstations for which the data path is
increased as a result of the break. If two breaks occur and they are
not both in the same section of cable, some workstations will be cut
off from some of the others. When system reliability is a critical
concern, a bus network or star network may prove superior to a ring
network. If redundancy is required, the mesh network topology may
be preferable.
Star Network
Star Network
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A star network is a local area network (LAN) in which all nodes
(workstations or other devices) are directly connected to a common central
computer. Every workstation is indirectly connected to every other through
the central computer. In some star networks, the central computer can also
operate as a workstation. The illustration shows a star network with five
workstations (or six, if the central computer acts as a workstation). Each
workstation is shown as a sphere, the central computer is shown as a larger
sphere, and connections are shown as straight lines. The connections can be
wired or wireless links.
In a star network, a cable failure will isolate the workstation that it links to
the central computer, but only that workstation will be isolated. All the
other workstations will continue to function normally, except that they will
not be able to communicate with the isolated workstation. If any workstation
goes down, none of the other workstations will be affected. But if the central
computer goes down, the entire network will suffer degraded performance or
complete failure. If redundancy is required, the mesh network topology may
be preferable.
Tree (star-bus) Network
Tree Network
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In telecommunication networks, a tree network is a combination of
two or more star networks connected together. Each star network is
a local area network in which there is a central computer or server
to which all the workstations or nodes are directly linked. The
central computers of the star networks are connected to a main
cable called the bus. Thus, a tree network is a bus network of star
networks. The illustration shows a tree network with five star
networks interconnected. The workstations are shown as small
spheres, the central computers of the star networks are shown as
larger spheres, connections within star networks are shown as short
lines, and the bus is shown as a backbone. The connections can
consist of wire cables, optical fiber cables, or wireless links.
Tree Network
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In a tree network, a cable failure in one of the star networks will
isolate the workstation that it links to the central computer of that
star network, but only that workstation will be isolated. All the
other workstations will continue to function normally, except that
they will not be able to communicate with the isolated workstation.
If any workstation goes down, none of the other workstations will be
affected. If a central computer goes down, the entire portion of the
network served by it will suffer degraded performance or complete
failure, but rest of the network will continue to function normally. If
the bus is broken, serious network disruption may occur.
Mesh Network
Mesh Network
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A mesh network is a network that employs one of two
connection arrangements, full mesh topology or partial mesh
topology. In the full mesh topology, each node (workstation or
other device) is connected directly to each of the others. In
the partial mesh topology, some nodes are connected to all
the others, but some of the nodes are connected only to those
other nodes with which they exchange the most data. The
illustration shows a mesh network with eight nodes. Each
node is shown as a sphere, and connections are shown as
straight lines. The connections can be wired or wireless.
A mesh network is reliable and offers redundancy. If one
node can no longer operate, all the rest can still communicate
with each other, directly or through one or more intermediate
nodes. Mesh networks work well when the nodes are located
at scattered points that do not lie near a common line.
Mesh Network
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The chief drawback of the mesh topology is expense, because of the
large number of cables and connections required. In some scenarios,
a ring network or star network may prove more cost effective than a
mesh network. If all the nodes lie near a common line, the bus
network topology is often the best alternative in terms of cost.
Network Characteristics
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Media used for connection
– Copper Cable
– Fiber Optic Cable
– Broadband Cable
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Speed of connection
Type of Signal
– Analog
– Digital
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Type of Data Movement
– Full Duplex
– Half Duplex
– Simplex
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Method of Movement
– Asynchronous
– Synchronous (polled)
Network Applications
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Email
Web Servers & Browsers
FTP Servers
Instant Messaging
Server no purpose without the network
Did not exist before networks were created
New applications created daily, weekly, annually
The Internet
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Wide area Network
Utilizes mesh topology
TCP/IP is protocol used to drive the network
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FTP
HTTP
HTTPS
Telnet