Transcript Presentation on Network Topology

3 Computing System
Fundamentals
3.4 Networked Computer Systems
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3.4.1 Network Topology
Network: definition
• A way of connecting computers so they can:
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share software (programs and data),
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allow communication.
share hardware (expensive peripheral
devices e.g. laser printers) and
• The computers and peripherals on a network
are collectively called nodes.
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LANs
• A Local Area Network (LAN) connects
nodes over a single building or site.
• They tend to use electrical cable or shortrange radio signals (wifi).
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WANs
• Wide Area Networks (WANs) operate over
much larger distances than LAN’s.
• They tend to use other communications
systems such as telephone lines, long-range
radio signals (wi-max), microwave links and
satellite links.
• The internet is a WAN.
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Network organisation
• Older LANs had a central mainframe
computer and associated non-processing
(dumb) terminals.
• Modern tendency in business is away from
mainframes towards networked PC’s
(workstations), which can also work as
stand-alone machines, connecting to a PC
working as a server.
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Network organisation
• The cost of a network is always greater than
that of the individual computers.
• Networks may be peer-to-peer (all
machines
equal) or there may be one or several
network servers, which control security and
hold users' files and other resources. Such
client/server networks are more common in
business.
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Network topology
• The four main LAN topologies (shapes) are
bus , ring, star and mesh.
• They may be connected to other networks via
bridges or routers and a large network will
probably be a hybrid type i.e. it will involve
two or more of these topologies.
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Bus topology
• Cheapest since they use a common cable or
backbone to which all devices are
connected.
• The cable must be properly terminated so
that signals are absorbed and don't bounce
up and down the bus.
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Bus topology
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Bus topology
• Bus networks can be fragile - a bad
connection or actual break can bring down
most of the network.
• Bus networks can be slow when large data
files are being transferred (they can only send
one message at a time).
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Ring topology
• Nodes are connected in a ring (bus with the
ends joined).
• More robust than a bus since data can go
round either way.
• An electronic token can be used to regulate
transmission (if a node has the token, it can
receive/transmit, if it is finished it passes the
token on).
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Ring topology
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Star topology
• Individual computers radiate out from the
server or via a switch or hub .
• The cabling is more expensive, but wifi is now
cheaper (wifi is always star).
• Vulnerable to a hub failure but if a cable
breaks the other computers still operate.
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Star topology
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Hybrid topology
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Mesh topology
• Nodes to several or many of their nearest
neighbours.
• Very reliable since data can be transmitted
along any of several routes (the network can
route around any failures).
• The internet is a mesh network.
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Mesh topology
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Node