Network StrategyThis is the way an organisation distributes the data across its network. It uses different types of networks to communicate the information across it.This is known as the Network Topology.

In the first section we will look at: Draw in jotterBus StarRing MeshTree

Topologies – Bus

TerminatorTerminator

Bus TopologyAdvantages:

•Easy to install because only needs one backbone.•Computers easily connected or disconnected by drop cable.•Inexpensive and good for temporary networks needed in a hurry.•If one node fails the rest still work data still travels along connection not through nodes.

TerminatorTerminator

Bus TopologyDisadvantages:

•If backbone is damaged then the whole network is down.•Terminators are required at each end disadvantage is that it takes time to attach them and they must be installed correctly. (Stops the data going back down the backbone causing interference).•Difficult to find the damage in the backbone. Moving terminator is one way of doing this but it is time consuming.•Not good to rely on a bus for a whole building (ok as temporary or add on to existing network)

Terminator Terminator

Topologies - Star

Star Topology

Connected to central hub or switch. All data passes through central hub. Hub can also act as repeater to boost the signal.The hub reads the destination address and passes it directly on to the correct IP address. More cable is needed but it makes it easy to add or remove nodes. (Just plug into cable outlet on wall).

Star Topology

Disadvantages:Much more cabling needed for star network.If central node fails all nodes are disabled.More expensive because of cost of hub/switch as the central node.

Advantages:Easy to install/remove a new node. No disruptions to network as this is being done.Easy to detect faults since it should only affect one node.

Topologies – Ring

Ring Topology

Nodes connected serially (one after another) in a circle. Signal travels in clockwise direction. Token needed to transmit data. It travels around the ring, when a computer wants to send message it grabs the token attaches the data and adds an address to it. This way only one message is travelling around the network at one time. No data collision. When the message has been received the receiving node sends back a message to the sending node the sender then releases the token back onto the ring. Each node boosts the signal as it travels around the ring.

Ring Topology

Advantages:Can increase the number of nodes without affecting the performance of the system.All nodes have equal access to the token and therefore have equal communication rights.Disadvantages:Most expensive because they specialist hardware.If one computer fails it may affect the rest of the nodes.

Topologies – Meshed

This is fully meshed

Mesh TopologyIn a true mesh all computers are connected to every other one. This is called fully meshed.

Fully meshed means if one node fails then the message can still travel to its destination. Fully meshed mostly used for backbone networks, i.e. the main connections between networks.

Partially meshed means all the nodes are not connected to every other one. Partially meshed means nodes may only be connected to another two nodes.

Mesh TopologyAdvantages:

If a connection is down then the data can easily travel along another route.

Disadvantages:Expensive, difficult to install because of so many connections.Difficult to manage because of complexity.Difficult to detect errors because of number of connections.

Topologies - Tree

Answer Questions page 56 of notes

Tree Topology

It is an interconnection of star topologies. It allows the expansion of existing networks.

Tree Topology -AdvantagesEasy to add new nodes, easy to add new segments.Easy to install and wire a tree network. Connect the central nodes and then the segments.Each device on the network has its own connect to the central node therefore no disruptions to network when connecting or removing devices.Easy to detect faults (only affects one node or segment).

DisadvantagesEach segment size depends on the type of cabling used. If a connecting node fails the network fails.More difficult to configure than the other networks.

Local Area Network (LAN )Network that is restricted to one room, building or site. LAN cables are commonly called UTP (Unshielded Twisted Pair). The maximum length of a cable is 1000m. Although cables can be linked together if a longer network is needed.LANs allow users to share peripherals such as printers and allow users to log on anywhere on the network.

Local Area Network (LAN )

Network StrategyNetwork Topology

Networks - LAN (Local Area Network) – in one building.

•Device Sharing.•Software Sharing.•Data Sharing.•Communication.

Wide Area Network (WAN )

WAN (Wide Area Network) – over a city, country or the world.Uses telecommunication - cable, satellite fibre optic.

Distributed Networks – lots of networks attached together.

Example is the internet

Networks

Client-Server Network Central server stores data files and log-in details.

Peer to Peer network No central server, all stations equal. Cheaper, data less secure.

NetworksNetwork Hardware

Network Adapter Card.Built-in to the computer.Allows the computer to send and receive data around the network.

Network Adapter CardStructured Cabling.

Cables made from copper wire, co-axial cable, fibre optic cable and twisted pairs.Twisted pair Ethernet most Common.Fibre Optic used to link over longer distances and to carry a very high bandwidth.

NetworksNetwork Software

Network Operating System – 2 parts

Part 1 - The version that runs on the server is needed to control which users and workstations can access the server, keep each user’s data secure. Control the flow of information around the network. It is also responsible for file and data sharing, communications between users and hardware and peripheral sharing.

Part 2 - The version that runs on the personal computers to turn them into network stations. Each workstation (computer) connected to the network needs the Network Operating System installed before it can connect successfully to the network facilities

NetworksNetwork Auditing and Monitoring Software.

This software keeps a track of network activity. It records user activity and workstation activity. In a commercial organisation this sort of auditing and monitoring can be used to detect fraud and suspicious activity.

Centralised or Decentralised

In the past decentralised because computing power was limited and could only handle the workload of a single department. A terminal attached to a mainframe. The terminal did not have a lot of computing power.

Then more powerful machines with more memory and processing power + networks + communications = centralised again.

There is still some decentralised computing - PCs and laptops for example.

Distributed DatabaseWhat is a

distributed database?

A distributed database is a database where different parts of the database or 2 or more files are located at different parts of the network.

Questions2008 Section 2Q15. A monthly report is produced by several employees creating

and editing sections of the document and then sending those to an editor over a Local Area Network.

(a)(i) Name a suitable topology for this Local Area Network and draw a diagram of this topology. 2

2006 Section 1

Q9. What is a distributed database? 2