NETWORK TOPOLOGIES
There are three basic
configurations used to connect
computers they are the
Bus
Ring
Star
Bus topology
 This type of network was widely used in the 1980’s
 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
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 one
computer with the address of another
computer attached to the message
 The message is broadcasted to all the
computers on the network until the
addressed PC accepts the message
How it worked
 The type of wires used for Bus Networks in the
80’s were called Thicknet and Thinnet
 A Thicknet cable (very large about 1 inch in
diameter usually yellow was hung around a room)
 Thinnet cables were connected to the PC’s NIC
and a Transceiver. The Transceiver was tapped
into 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 50Ω
resistors
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
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 Ring
network
How this Topology works
 a node has information to send to another
computer on the network so it sends the
information out on the network to the PC it is
connected to, if the information is for this PC (the
recipients NIC address is attached to the
message, which is like putting an address on an
envelope) 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
How it Works
 As it is better to have computers take turns
using the connecting Data cable, Ring
topologies 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
Problems and Solutions
 The drawback to this type of topology is that a single
malfunctioning workstation can disable the whole network
 To make sure all the information is sent the receiving PC
sends 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 1980’s
 This type of network used Thinnet cable joining nodes.
 In the mid 1980’s Thinnet cable was replaced by
Category 3 Ethernet cable capable of handling up to
10Mbps
Star topology
HUB
 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
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
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
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
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 of ports that each
accepts a network cable
 Small hubs can network four computers
together
 They contain four or sometimes five ports
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
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 through
them and are not aware of their source or
destination
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 computer network
Different Types of Hubs
 Technically speaking, three different types of
hubs exist
Passive
Active
Intelligent
Passive hubs
 Passive hubs do not amplify the electrical
signal of incoming packets before
broadcasting them out to the network
Active hubs
 amplify the electrical signal of incoming
packets back to their original level before
broadcasting them back out on the network
Intelligent hubs
 add extra features to an active hub that are
of particular importance to businesses
 An intelligent hub is typically stackable (built
in such a way that multiple units can be
placed one on top of the other to conserve
space).
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
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
Network Switch
 Network switches appear nearly identical to
network hubs, but a switch generally
contains 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 and
destination device of that packet, and
forwarding it appropriately
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
What is a Router?
 Routers are physical devices that join
multiple wired or wireless networks together
 Technically, a wired or wireless router is a
Layer 3 gateway, meaning that the
wired/wireless router connects networks
together
 A Gateway is a device that acts like a
security guard and only allows data in or out
if it has the right network headers
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 person
you are speaking to).
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 PC’s to access the Internet using
only one address.