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

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

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

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

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

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

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