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NETWORK TOPOLOGIES
There are three basic
configurations used to connect
computers they are the
Bus
Ring
Star
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Bus topology
This type of network was widely used in the 1980s In this configuration every computer (node) shares
the networks total bus capacities.
In this configuration adding more computers will
reduce the access speed on the network. Each computer communicates to other computers
on the network independently this is referred to as
PEER-TO-PEER networking
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How a Bus Peer to Peer
Network Works
All computers on a network have a distinct
address just like your house does
a message would be send from onecomputer with the address of another
computer attached to the message
The message is broadcasted to all thecomputers on the network until the
addressed PC accepts the message
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How it worked
The type of wires used for Bus Networks in the80s were called Thicknet and Thinnet
A Thicknet cable (very large about 1 inch indiameter usually yellow was hung around a room)
Thinnet cables were connected to the PCs NICand a Transceiver. The Transceiver was tappedinto the Thicknet cable
To stop the message from bouncing back and
forward down the wire (known as signal bounce)both ends of the network are terminated with 50resistors
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Problems
One of the main problems with this type of
network is that it is not very fault tolerant, a
break or defect in the bus would affect the
whole network
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Ring Topology
In Ring topology each node is connected to the
two nearest nodes so the entire network forms a
circle
Data only travels in one direction on a Ringnetwork
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How this Topology works
a node has information to send to anothercomputer on the network so it sends theinformation out on the network to the PC it isconnected to, if the information is for this PC (the
recipients NIC address is attached to themessage, which is like putting an address on anenvelope) then the PC accepts the data
otherwise it passes the information on to the next
PC by repeating the data back out on the line This method of repeating the data helps keep the
integrity of the data readable by other computers
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How it Works
As it is better to have computers take turnsusing the connecting Data cable, Ringtopologies incorporated a system called
Token passing In this topology, to transmit on the wire your
computer must have control of the token or
wait for the token to be free Larger Token Ring networks use multiple
tokens
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Problems and Solutions
The drawback to this type of topology is that a singlemalfunctioning workstation can disable the whole network
To make sure all the information is sent the receiving PCsends the token back to the sending PC after it has
received all the data If the sending PC is finished sending it passes the token to
the next PC
This type of network was also widely used in the 1980s
This type of network used Thinnet cable joining nodes.
In the mid 1980s Thinnet cable was replaced byCategory 3 Ethernet cable capable of handling up to10Mbps
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Star topology
In a Star topology every node is connected
through a central device such as a Hub,
Switch or Router Compared to a Ring or Bus topology a Star
topology requires that more thought be put
into its setup
HUB
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The Good and Bad of a
Star Network
The upside of a star network is that if any
one cable fails then only the node
connected on that cable would be affected
Another positive point to this type of network
is that it is very simple to join two star
networks together by connecting their
central devices to each other
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The Good and Bad of a
Star Network
As each computer is connected to a central
device (Hub) the location of the Hub must
be made as central as possible, so as to
reduce cable lengths
The drawback to this type of topology is if a
central device was to fail then all computers
connected to that device would not be able
to see the network
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What is a Hub?
A hub is usually a small rectangular box,
often made of plastic, which receives its
power from an ordinary wall outlet
A hub joins multiple computers (or other
network devices) together to form a single
network segment
On this network segment, all computers can
communicate directly with each other
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What is a Hub?
Ethernet hubs are by far the most common
type, but hubs for other types of networks
such as USB also exist
A hub includes a series ofports that each
accepts a network cable
Small hubs can network four computers
together
They contain four or sometimes five ports
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What is a Hub?
Many times the fifth port is reserved for
"uplink" which is the connecting of one hub
to another hub or similar device (joining two
segments together).
Larger hubs contain eight, 12, 16, and even
24 ports
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Key Features of Hubs
Hubs classify as Layer 1 devices in the OSI model
OSI stands for :
The Open Systems Interconnection Basic Reference
Model
At the physical layer, hubs can support little in the
way of sophisticated networking
Hubs do not read any of the data passing throughthem and are not aware of their source or
destination
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Key Features of Hubs
Essentially, a hub simply receives incoming
packets, possibly amplifies the electrical
signal, and broadcasts these packets out to
all devices on the network - including the
one that originally sent the packet!
a packet is a formatted block of data carried
by a computernetwork
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Different Types of Hubs
Technically speaking, three different types
of hubs exist
PassiveActive
Intelligent
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Passive hubs
Passive hubs do not amplify the electricalsignal of incoming packets before
broadcasting them out to the network
Active hubs
amplify the electrical signal of incomingpackets back to their original level before
broadcasting them back out on the network
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Intelligent hubs
add extra features to an active hub that areof particular importance to businesses
An intelligent hub is typically stackable (built
in such a way that multiple units can beplaced one on top of the other to conserve
space).
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Intelligent hubs
It also typically includes remote
management capabilities via SNMP and
virtual LAN (VLAN) support (You can
configure or check it from a computer that is
connected to it).
SNMP-Simple Network Management
Protocol
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What is a Network Switch?
A network switch is a small hardware
device that joins multiple computers
together within one local area network (LAN)
Technically, network switches operate at
layer two (Data Link Layer) of the OSI model
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Network Switch
Network switches appear nearly identical tonetwork hubs, but a switch generallycontains more "intelligence" (and a slightly
higher price tag) than a hub Unlike hubs, network switches are capable
of inspecting data packets as they are
received, determining the source anddestination device of that packet, andforwarding it appropriately
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Network Switch
By delivering each message only to the
connected device it was intended for, a
network switch conserves network
bandwidth and offers generally better
performance than a hub
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What is a Router?
Routers are physical devices that joinmultiple wired or wireless networks together
Technically, a wired or wireless router is a
Layer 3 gateway, meaning that thewired/wireless router connects networkstogether
A Gateway is a device that acts like asecurity guard and only allows data in or outif it has the right network headers
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Routers
Home networkers often use an Internet Protocol
(IP) wired or wireless router
IP is the most common OSI network layer protocol
Protocols are the rules governing the transfer of
data information, it can also be compared to how
humans use languages (to get your point across
you must talk in the same language as the personyou are speaking to).
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Routers
An IP router such as a DSL or cable modem
are broadband routers and joins the home's
local area network (LAN) to the wide-area
network (WAN) of the Internet
A Broadband Router is a device that allows
multiple PCs to access the Internet using
only one address.
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