Download networks

NETWORKS
• NEED
• HISTORY
• HARDWARE REQD.
• SOFTWARE REQD.
• TOPOLOGIES
NETWORK TOPOLOGIES
• Topology – Layout, like a map
• Two types : Physical and Logical
• Physical - layout of cables,
computers, peripherals (Roads etc)
• Logical - method used to pass the
information between computers
(Traffic Flow – Cars, Density, Jam)
PHYSICAL TOPOLOGY
• virtual shape or structure of a
network
• Actually may not correspond to the
physical design of the devices on the
computer network
• e.g. computers on the home
network may be arranged in a circle does not necessarily mean that it
presents a ring topology
PHYSICAL TOPOLOGIES
• Many Types as per history, needs
• We take a few standard ones
• Bus, Hub or Star, Ring, Mesh
• Hybrid – StarBus(Tree), StarRing
• Most common - Star Topology
BUS TOPOLOGY
• Uses a Cable as a backbone
• Thinnet (10base2) or Thicknet
(10base5) coaxial cable used
• Various Computers like Bus Stops
• Workstations connect DIRECTLY to
the backbone
• Terminals at the two ends like
“shock absorbers” so that signal
does not reflect back (“Bus Parks” RBS,BHU)
BUS TOPOLOGY
• The device, which wants to
communicate, sends the broadcast
message
• All the devices attached with the
shared cable receive it
• Only the intended recipient accepts
and processes that message.
BUS TOPOLOGY
BUS TOPOLOGY
• Easy to install and don’t require
much cabling
•Any defect in the main cable (Bus)
results in breakdown of network
• As computers increase, traffic
becomes too much
• So good only for small networks
(upto 10 workstations)
• Old – not in much use now
HUB OR STAR TOPOLOGY
• Most Common – Popular because of
low cost & ease of troubelshooting
• All workstations connected to a
central “device” – hub or switch
• Evenif one workstation fails, the
network goes on working for the rest
• But if the hub/switch fails, the entire
network is down
HUB OR STAR TOPOLOGY
HUB OR STAR TOPOLOGY
• A HUB transmits data to all the
nodes (normally “passive”)
• An “active” hub is a “multiport
concentrator” (A “repeater” is a
“concentrator”) – amplifies
• A Switch maintains “switching
tables” & sends to “destination”
• Hubs & Switches are specified
by the number of “ports”
HUB OR STAR TOPOLOGY
• On bigger networks & gateways, a
“router” used
• A “gateway” is connection between
two networks
• Routers keep “route tables” and are
programmable
• More devices in Star topology
RING TOPOLOGY
• Computers connected on a single
circle of cable
• Unlike the bus topology, there are
no terminated ends
• The signals travel around the loop
in ONE direction
• every computer or devices has two
adjacent neighbors for
communication
RING TOPOLOGY
RING TOPOLOGY
• Signals pass through each
computer which acts as a “repeater”
to boost the signal and send it to the
neighbour
• FDDI, SONET or Token Ring
Technology can be used
• A token is a special series of bits
that contains control information
• The token allows a workstation to
transmit data to the network
RING TOPOLOGY
• Used only for small networks,
earlier
• Any damage of the cable of any
cable or device can result in the
breakdown of the whole network
• Has become almost obsolete.
MESH TOPOLOGY
• Each computer connected to every
other computer by a separate cable
• Partial (not complete) mesh has each
computer connected to more than one
(also called Graph Topology)
• Provides redundant paths
• If one computer fails, the network
does not stop
MESH TOPOLOGY
•Router works in finding the routes
for the messages and reaching them
to their destinations.
• When every devices connects to every
other device -full Mesh topology
• In the partial mesh every device
indirectly connected to the other devices.
MESH TOPOLOGY
MESH TOPOLOGY
• On a large scale, multiple LANs
connected using mesh topology
• Leased telephone lines, Thicknet
coaxial cable or fiber optic cable used
• The big advantage - its backup
capabilities by providing multiple
paths through the network
• Hence used on the Internet
MESH TOPOLOGY
• Works on the concept of routes
• The message finds its route for its
destination
• Message sent to the destination can
take any possible shortest, easiest
route to reach its destination
• In Bus, Star topologies messages are
usually broadcast to every computer
• In Ring topology message can travel
in only one direction
HYBRID TOPOLOGIES
• In hybrid topology, two or more
topologies combined to form network
• These are the most common in use.
• For example, a combination of a star
and bus topology
• May be used in a campus network
• Each LAN a “star”, LANs connected
in a “ring”
STAR-BUS OR TREE TOPOLOGY
• Several star topology networks are
linked to a bus connection
• If a computer fails, it will not affect
the rest of the network
• However, if the central hub, that
attaches all computers in a star, big
problems since no computer will be
able to communicate.
STAR-BUS OR TREE
TOPOLOGY
STAR-BUS OR TREE TOPOLOGY
• Only the hub devices can connect
directly with the tree bus
• Each Hub functions as a root of a
tree of the network devices
• Supports future expandability of the
computer networks, much better than
a bus or star
STAR-RING TOPOLOGY
• Computers are connected to a central
component as in a star network
• These components, however, are
wired to form a ring network
• Like the star-bus topology, if a single
computer fails, it will not affect the rest
of the network
STAR-RING TOPOLOGY
STAR-RING TOPOLOGY
•By using token passing, each
computer in a star-ring topology has
an equal chance of communicating
• Allows for greater network traffic
between segments than in a star-bus
topology.
SUMMARY
• Topologies important part of the
network design
• the knowledge of & the difference
between each topology essential
• Also necessary is knowledge of each
network device to design a network
• Badly designed network can result in
waste of time in troubleshooting