Topic 19- Networks

What is a computer Network?:

• A network is two or more compters that are linked together so that they are able to share resources, such as a printer, scanner, software and data

Shared resources include:

• Hardware- printers, scanners, storage, etc
• Software- need only to be installed on one computer
• Data
• An internet connection

2 types of networks:

• There are two specfic types of networks:
• LAN (Local Area Networks)
• WAN (Wide Area Networks)
• Basically a WANis much bigger type of network and spread over a much larger georgraphical area

LANs and WANs

Local Area Networks:

• Confined to a small area
• Usually located in a single building
• Use cables, wireless, infrared and microwave links that  are usually owned by the organization
• Cheap to build
• Cheap to run

Wide Area Networks:

• Cover a wide geographical area
• In lots of different buildings and cities, countries
• Use more expensive telecommunication links that are supplied by telecom companies
• Expensive to build 
• Expensive to run

Network Topologies/configurations:

• The device in a network may be arranged in different ways. Each way is called a topology
• The devices are the computers, printers, scanners

Star Network Configuration:

• In a star network layout, each workstation is connected by its own cable directly to the server. Star networks are usually the layout of choice in schools and offices because they tend to be the most reliable of the topologies

Ring Network Configuration:

• In a ring network layout, all of the computers are connected to one another in a circle. The data passes from one computer to the next one and then all the way around the ring layout until it reaches the destination computer

Bus Network Configuration:

• A single cable joins all of the workstations, printer, file server and other components together. At each end of the bus is a "terminator". This is a piece of hardware which prevents signals bouncing back and forward

Characteristics of Networks:

• Internet and the WWW (World Wide Web)
• These are not the same thing
• Internet- a huge froup of networks joined together, each of which containg smaller networks. This means the Internet contains hardware
• WWW- a means of accessing information contained on the Internet. An information sharing model built on top of the internet. Use http, a language, to transmit information.

Intranets:

• A private network that uses the same technology as that used by the Internet for sending of messages around the networks
• Main use of an Internet is to share organisational information and reources

• The concept of Client Server is used along witht eh same photocols-http, FTP. email
• Main feature of an Internet is that only employes of the organisation are able to use it
• Not necessarily confines to one site and the Internet will still be freely available

Extranets:

• Intranets are restricted to employees of an organisation whereas an Extranet is accessible by customers, suppliers and other partners
• This is feasible by the username and passwords
• As every one may not be on the same site data needs to be send using 3rd party communication lines
• When the internet is used to send data, gateways, firewalls, encryption and user authentication must be used

An ICT network consits of:

• Hardware/ communication devices
• Network software

• Data transfer media

Communication devices:

A network interface card:

• Prepares data for sending over the network
• Sends the data
• Controls the flow of data

A hub:

• Is used to join computers ina network
• Allows the connection of cables
• Allows the sharing of files and Internet access

A switch:

• Is similar to a hub but more intelligent

• Can look at a packet of data to decide where it should go
• Reduces the number of packets of data on a network, which speeds it up

A router:

• Can be wired or wireless
• Is used to join several networks together
• Is often used to connect devices Computers in the home to the internet

Brides:

• These are devices that connect separate LANs together to form on large LAN

Gateways:

• This is a device or software that translates between two different kinds of computer network, for example between a LAN and a WAN

Network software:

Network software consists of:

• Network operating systems- specialist operating systems designed specifically for networks
• Network management software- used to help a network manager run a network by keeping track of software, keeping software up-tp-date, installing software security patches, helping to manage the help-desk, etc

Data transfer media:

The medium/method by which the data is transferred in a netowkr can be:

• Metal wire
• Fibre optic cable
• Wireless

Advantages and disadvantages of network systems:

What are the advantages of networked computers over a stand alone computer:

Advantages:

• Improved security- work can be saved on the network. The network manager will make sure tat the work is back up. Password make sure that other people cannot access your work unless you want them to
• Speed- it is very quick to copy and transfer files
• Cost- when software is bought, the schools can buy network versions. These are much cheaper tan buying a copy for each stand-alone computer
• You can share hardware- you can just have one printer and one scanner, as any of the computers connected to the network can use them
• Software can be installed in one place- you do not install software on each computer. This makes it faster to install and easier to maintain. f the software needs to be upgraded, then this is mich easier if only one copy is used
• Eamil facilities- any user of the network will be able to communicate using electronic mail. This will be much more efficient compared to paper-based documents such as memos, etc
• Access to a central store of data- users will have access to centerally stored data

Disadvantages:

• A network manager will need to be employed- this can be quite expensive 
• Security problems- a virus could get onto the system and cause problems, or hackers may gain access to the data on the networks
• Breakdown problems- if the network breaks down, users will not have access to the important information held
• Expensive- a server and cables and/ or other communication devices will be needed. The installation costs of a network are also high

Intergrated Point of Sale System (POS):

• POS systems are where you pay for goods in a store. They are networked together.This means when an item is sold and its bar code is scanned, the system looks up the price and description details to print out an itemized receipt. At the same time the system will deduct an item from the stock so the stock control system is kept up to date

Hardware used at a POS:

• Bar code reader/laser scanner- this is used to input a number that is coded in the bar code as a series of light and dark lines
• Keyboard- the keyboard is used to enter codes on items if the bar code is damaged
• Touch screens- these are often used in restaurants where there are no goods to scan
• Swipe card readers- there are used to swipe to magnetic strips on loyalty cards
• Chips and pin reader- there are used by customers to insert their credit/debit card containing a chip.The system then asks them to enter their PIN (personal identification number) whihc is a number only they know and this proves to the system that they are the genuine owner of the card

Other systems connected to the POS:

POS terminals are connected via networks to other systems such as:

• Loyalty card systems- where customers are given loyalty points according to how much they spend
• Accounts systems- where the money coming into the shop is accounted for

• Automatic stock control systems- they system knows what has been sold, so that is can automatically recorded more one the stock falls below a certain amount
• Payment systems- where the customers can pay using credit/debit cards

Automatic Stock Control:

• When an item is sold at the POS terminal the number of that particular item is reduced by one. This means the computer know s how many items of are in stock. Once the number of items has fallen below a certain level the computer system will automatically order more stock from the supplier. This means the shop should never run out so popular selling items