Chapter 5: Networking Flashcards
Network
A collection of computers and peripheral devices connected together
What are a few types of networks?
- LANs
- WANs
- MANs
LAN
Local Area Network: a collection of computers and peripherals connected together within a limited area
What kind of areas are LANs used in?
- Residences
- Schools
- Laboratories
- Office buildings
WAN
Wide Area Network: a collection of computers and LANs connected together over a large geographical area, often using leased infrastructure
MAN
Metropolitan Area Network: spans an entire city or campus, formed by connecting together multiple LANs
Order the following network types in ascending order of size:
- MANs
- WANs
- LANs
3 1 2
What three main categories does the use of networks benefit?
- Sharing resources
- Communication
- Centralised management
Advantages of using networks for Sharing Resources (3)
- Shared resources can be accessed anywhere on the network from any computer
- Ability to use shared peripheral devices, e.g. printers and scanners
- Internet connection can be shared
Advantages of using networks for Communication (3)
- Email can be used to communicate with colleagues
- Messaging systems can be used to chat while working
- Files can be transferred between computers easily
Advantages of using networks for Centralised Management (4)
- User profiles and security can all be managed centrally
- Software can be distributed across the network as opposed to individual installation
- Users can use any PC on the network and access their own files
- Data can be backed up centrally
Disadvantages of using networks (5)
- Purchasing network cabling and file servers can be costly
- Managing a large network is complicated and requires training. A network manager usually needs to be employed
- If the file server goes down, files on the server become inaccessible. The computers can still be used, but are isolated
- Viruses can spread to other computers throughout a computer network
- Risk of being hacked, especially with WANs. Security measures, e.g. a firewall, are needed to prevent this
Network topology
A schematic description of the layout of a network
Bus Network
A topology where each device is connected to the main cable, referred to as the bus. Any device can transmit at any time, but only one transmission can occur along the main bus at any one time
Pros and Cons of Bus Networks (3 | 4)
Pros
- Easy and inexpensive to install
- Easy to add new computers to network
- Broadcasting onto a bus is faster than transmitting around a ring network through many devices
Cons
- Main cable failure leads to the whole network going down
- Cable failures hard to isolate: affects all attached computers
- Not secure - all data broadcasted on one cable
- Performance slows down as the amount of traffic increases
Ring Network
A topology where each device is connected to the next in a loop. Uses a token-passing protocol to manage transmission one device at a time
Pros and Cons of Ring Networks (3 | 3)
Pros
- Not dependent on a central computer
- Token passing protocol is simple and reliable
- Consistent performance even when there is a lot of traffic
Cons
- A single node or link failure could potentially disrupt the whole network
- Not secure - all connections shared
- Slow - data goes around the whole network
Star Network
A topology where each device has its own cable connecting it to a central device, which can be a switch or server
Pros and Cons of Star Networks (4 | 2)
Pros
- Failure of a cable only affects one station
- Consistent performance even when the network is heavily used
- Easy to add new computers
- Most secure - messages transmitted down unshared links
Cons
- Can be costly to install - lots of cabling needed
- Dependence on a single switch: if this fails, the whole network goes down
What kind of networks are the following topologies used in:
- Ring?
- Bus?
- Star?
- LANs and MANs
- LANs only
- LANs and WANs
What two ways can the computers in networks be configured to behave in?
- Client-server
2. Peer-to-peer
Peer-to-peer
A method of organising devices in a network where all devices are of equal status instead of being designated specialised roles. Every computer can access resources on another computer, provided access rights have been granted
How are the computers in a peer-to-peer network connected together?
They are cabled together to form a LAN
Why might a small company use a peer-to-peer network?
It is not cost-effective to have a specialised server
Peer-to-peer: 1. Computer status 2(+/-). Setting up and maintenance 3(+/-). Management 4(+/-). Backing up 5(+/-). Dependency 6. Usage 7(+/-). Number of computers
1. All computers have equal status 2+. Easy to set up and maintain 3-. No centralised management - less secure 4-. Each computer backed up separately 5+. No dependency on a server 6. LANs only 7-. Impractical for over 10 computers
Client-server
A method of organising devices in a network where some computers have roles as servers. These provide resources and services to other computers, known as clients. Management of the network and shared resources and files is centralised at the server
What are the two kinds of computers used in a client-server network?
- Servers: holds data and controls access
2. Clients: where the user actually works
What is the job of a server computer? (3)
- To control access to shared resources e.g. files, printers
- Where all the data is stored, making data storage centralised
- May have specialised roles e.g. print servers, dedicated to controlling access to shared printers and queuing print jobs
How do client and server computers interact with each other in school systems? (4)
- User logs onto client computer using login details
- Client computer connects to the server
- Server verifies user login
- Server gives user access to files they have permission for
How can a client-server network approach be used across a WAN? (2)
- The browser acts as a client to the web server, which is somewhere in the world
- Companies have centralised databases, which are accessed across a WAN by applications on client computers
Why is the client-server architecture used across a WAN?
It means that the data can be stored in one place, and can still be accessed by a large number of client devices worldwide
Client-server: 1. Computer status 2(+/-). Setting up and maintenance 3(+/-). Management 4(+/-). Backing up 5(+/-). Dependency 6. Usage 7(+/-). Number of computers
- Specialised roles of either clients and servers
2-. Needs a network manager to run the network or web server
3+. Centralised security and management
4+. Backup done from central server
5-. Dependent on central server - Large LANs and WANs
7+. Can contain hundreds of computers
What is the basic principle of a client-server system? (3)
- The client requests data
- The server processes the request
- The server returns a response accordingly
Fill in the blanks:
In client-server architectures, there are __ distinct parts to the coded solution, with a __________ between them. Part of this solution will execute at the __________, part at the __________.
- 2
- Network connection
- Server end
- Client end
Internet
A global computer network providing a variety of information and communication facilities through the use of standardized communication protocols
What kind of network is the Internet?
A WAN
World Wide Web
An information-sharing model that is built on top of the Internet, making up a subset of the Internet
What are some examples of things that are part of the Internet, but not part of the World Wide Web? (4)
- Email (relies on a mail transfer protocol)
- Instant messaging OR Internet Relay Chat (IRC)
- Internet gaming
- File Transfer Protocol (FTP)
Protocol
A set of rules that defines how information is transferred over the Internet
HTTP
HyperText Transfer Protocol: the set of rules for transferring files on the World Wide Web
What happens when a browser requests a webpage using HTTP? (3)
- Browser requests webpage
- Server finds page
- Webpage is sent back to the browser
Standalone applications:
- Data storage
- Network connection
- Number of users
- Availability needed
- Code structure
- Security measures
- All data stored locally (disk or main memory)
- No network connection to manage
- Single
- Used as needed, can be closed between uses
- Modular structure less important
- Local access rights on host PC is sufficient security
What happens when a browser sends a request for product information using a form on a webpage, which is connected to a database? (3)
- Browser sends SQL data request
- Server selects data from database from database and completes page
- The webpage with the relevant data filled in is returned to the browser
Client-server applications:
- Data storage
- Network connection
- Number of users
- Availability needed
- Code structure
- Security measures
- Data must be passed between the client and server
- Must manage a network link
- Multiple clients per server, so a request queue must be managed
- Must be available all the time
- Must be designed and created in a modular fashion
- Clients have to be authenticated before data sent to them
Handshake
The communication between a client and server device that initiates communication
Three-way handshake
The TCP/IP handshaking process that consists of three exchanges
What are the steps of the three-way handshake? (3)
What is the result?
- The client sends a SYN to the server
- The server sends back the client’s SYN with an ACK
- The client sends back an ACK
The client can now communicate with the server.
What is:
- A SYN?
- An ACK?
- A synchronisation request
2. An acknowledgement
TCP/IP
Transmission Control Protocol/Internet Protocol: the basic communication language of the Internet
Static webpage
The contents of the page are all coded into the page itself i.e. it does not have any content that updates automatically
Dynamic webpage
A webpage that is populated from a database, meaning that its contents are always current
Server end programming
Code that is executed at the server side of a client-server system
Client end programming
Code that is executed by the browser at the client side of a client-server system
What happens when an Internet sales company makes a website? (3)
- A basic page layout is made
- This is populated with relevant product details
- Contents are usually based on search criteria
What are some examples of client-side programming? (4)
- Storing data in cookies
- Validating data form entries
- Flash animations and Java applets that run on a page
- Displaying pop-up ads when the mouse hovers over keywords
Validation
Where the computer software checks that data entered by the user is sensible and conforms to any defined rules
Examples of validation checks carried out on the client end (5)
- Range
- Type
- Length: e.g. password length longer than 8 characters
- Presence: makes sure needed information is entered
- Format: e.g. postcode, email address
What does validation do?
It checks that entered data is reasonable, not whether or not it is correct
What does verification do?
It double-checks that data is entered correctly e.g. passwords, email addresses
Cookies
Stored on the client computer, used by websites to store data which makes the pages more user-friendly
What is an example of what cookies do to make a page more user-friendly?
Prompting the user when they enter a username or search for something on the website
Applets
Small client-end programs that are embedded in webpages
What are some examples of server-side programming? (5)
- Retrieving data from a database
- Populating a page with the latest details
- Checking usernames and passwords
- Some forms of validation e.g. existence checks
- Counting the number of site visitors
HTML
Hypertext Markup Language: defines the content and structure of a webpage using tags
CSS
Cascading Style Sheets: defines how components within a page will be styled using selectors
When creating a website, what is it considered good practice to do?
Use HTML for content and CSS for styling, as opposed to using inline styles
How was the content of webpages arranged in the past? (2)
- The content and style were mixed together
2. In order to get a semblance of webpage design, content such as images were placed in invisible tables
Markup language
A language designed for the processing, definition and presentation of text
Scripting language
A language that allows you to record a set of repeatable instructions
What are a couple of examples of web scripting languages?
- PHP
2. ASP
How can Python be used in web scripting?
Through the use of a special library such as Django
