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)

• 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

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

•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

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