SHAPE OF A NETWORK

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TOPOLOGY

• The way the computers are cabled together

• Four different layouts

• Logical topology describes the way data travels across the network

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FOUR TYPES

• Bus Network

• Star Network

• Ring Network

• Mesh

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BUS NETWORK

• Simplest/easiest

• Linear

• Single cable – trunk

• Computers are passive participants

• Any computer (node) can pass a message

• Transmissions are limited to one computer at a time – one computer is the master

• Other computers must wait until the line is free

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COLLISION

• Data runs into each other• Both nodes must back off and wait for line to be free• Single bounce – caused by single that continues

uninterrupted to the end of the bus and then keeps bouncing back and forth along the cable, keeping other nodes from using the line

• Terminator – absorbs signals and keeps them from bouncing back along the trunk – usually only in BUS networks

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DISRUPTING COMMUNICATION

• Break in the cable

• Physically separated

• One end is disconnected

• All activity stops

• Computers can still function as stand-alone

• Just can’t communicate or share resources

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NETWORK EXPANSION

• Cable in a bus network can be expanded in one of two ways:• Barrel connector – connects two pieces of cable to make

longer• Connectors weaken signal

• Continuous cable is preferable

• Repeater – used to connect two cables• Boosts signal before it sends it on its way

• Better than connector because allows signal to travel further and still be correctly received

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ADVANTAGE/DISADVANTAGE• Advantages

• Easy to implement and extend• Well suited for temporary networks (quick setup)• Initially less expensive than other topologies• Cheap

• Disadvantages• Difficult to administer/troubleshoot.• Limited cable length and number of stations.• If there is a problem with the cable, the entire network goes down.• Performance degrades as additional computers are added or on heavy traffic.• Low security (all computers on the bus can see all data transmissions).• Proper termination is required.(loop must be in closed path).• If many computers are attached, the amount of data flowing causes the network

to slow down.

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STAR NETWORK

• Like arms of octopus• Stretches out in different directions• Hub /Switch – device in the middle • Hub / Switch– connects nodes in the arms• Hub/Switch participates actively in the network boosting

signals as they pass• It can be a passive wiring panel that simply relays

transmission through the network

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ADVANTAGES/DISADVANTAGES• Advantages• Centralized resources and management

• Very expandable

• Nodes added easily

• Problems are easier to find

• Break in cable brings down only the node directly affected

• Disadvantages• Requires great deal of cable

• If central point fails, everything shuts down

• More expensive to install

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RING NETWORK

• Nodes form a circle• Data is quickly transferred without a ‘bottle neck’. (very

fast, all data traffic is in the same direction)• Each node communicates with only two others:• The one that transmits to it • The one to which it transmits

• The failure of one node can bring down the whole system

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TOKEN PASSING

• A way to avoid collisions and help data run smoothly• Computers pass a small collection of bits – tokens• A node has to wait until it has a token to transmit data• Computer then modifies token to let other nodes know

that a token is in use• Token travels at speed of light – 186,000 miles per

second

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ADVANTAGES/DISADVANTAGES• Advantages

• Each node has equal opportunity to transmit

• Do not require a lot of cable or fancy equipment

• The transmission of data is relatively simple as packets travel in one direction only.

• Disadvantages

• Problems are difficult to find

• Total dependence upon the one cable

• Break in cabling brings down network

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MESH NETWORK• Computer is connected to every other computer by separate cable

or by wireless

• Uses mainly for Backbone networks

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ADVANTAGES/DISADVANTAGES

• Advantages

• Provides redundant or backup paths

• If one cable is broken, another takes over the traffic

• Easy to find problems

• Disadvantages

• Expensive to install because of all the cabling – Wireless connectivity can alleviate the cable cost but can be less reliable than cable and less bandwidth.

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SUMMARY OF NETWORK TOPOLOGIES

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TopologyPerformance with few nodes or low network

traffic

Change in performance with many nodes or high

network traffic

Ease of troubleshooting

(compared to other topologies)

Cost of installation (compared to other

topologies)

Ease of setting up and modifying (compared to

other topologies)

Problems to the network caused by cable or node

failure

LINE (BUS) Medium Most affected Fairly easy Low Easy to set up and modify

Failure of the bus cable causes total failure. Failure

of a node has no affect.

RING Slow Least affected Hard High Easy to set up but harder to modify

Cable or node failure causes total network failure.

STAR FastSome affect but the

switch/hub can be upgraded easily

Easy High Easy to set up and modify

Cable or node failure only affects that node. Failure of the hub/switch or the server causes total network failure

ASSIGNMENT 1 • List the 4 types of topologies:

• _____________ _______________ _________________ _________________

• Which topology is probably the least expensive initially? __________________

• This type network requires a hub or switch: _______________________

• A _____________ network is the network behind the network for extreme bandwidths and high speed data.

• This type network would be the most reliable, but the most expensive to use if using wire or fiber, so mostly only used in backbone networks: ___________________

• Collisions between data occur mostly in this type network, especially when the network grows to large: _______________________

• All the nodes in this type network form a closed circle and pass tokens: ____________

• These two types of network shapes are mainly used for backbone networks:

• _________________________ __________________________

ASSIGNMENT 2

• Select the type of network you think based on the scenario:

• BUS / STAR / RING / MESH

• The node in this network failed, and brought down the entire network: __________

• A cable was cut but only brought the one client down: ____________

• The problem appears to be the switch, may need replaced: _________________

• We are using wireless instead of wire, we’ll have tons of redundancy but will be to expensive to use wire: ___________________

• A cable cut had brought down the entire network: __________________

• It was easy to setup this network, but going to be hard to modify_____________

• We’ve had to add 10 clients, now up to 20, the network speed is terrible:_____________

• Adding a client is just connecting another wire into the switch: _______________

ASSIGNMENT 3

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NODE SWITCHNODE NODE

NODE

NODE NODE

Given the scenario:Construct and draw a network diagram for: 5 Nodes

Using the following symbols

For each type network create a slide: Bus network / Star Network/ Ring Network

So there will be a total of 3 networks, one on each slide.

Example of a mesh network with the symbols given: