Networks

• What is a Network A network is a set of interconnected devices that can commumnicate with eachother through exchanging data.
• What is the purpose of a network To enable datasharing between devices Allows commnunication between two or more users
• What is a protocol A protocol is a set of rules that are responsible for data transmission
• What is the importance of protocols Protocols ensure there is a successful and secure transmission of data and helps maintain efficiency during communication.
• Examples of protocols TCP IP UDP FTP HTTP/HTTPS SMTP IMAP POP
• What is a standard A standard is a set of specifications that govern how a product should function
• What is the importance of standards Standards ensure different devices from various manafacturers can communicate seamlessly regardless of their model. Standards ensure there is compatability and consistency across different devices.
• TCP Transmission Control Protocol Protocol that provides error free transmission between two routers.
• IP Internet Protocol Protocol which routes packets across a WAN.
• UDP User Datagram Protocol Protocol that uses a simple connectionless transmission model. Behaves like TCP except it has no error checking. Used for areas where speed is more important than accuracy.
• HTTP/S Hyper Text Transfer Protocol Protocol that allows a client and server to send and recieve requests and deliver HTML webpages. S stands for secure. This adds encryption.
• FTP File Transmission Protocol Protocol that is used for sending files between computers normally on a WAN.
• SMTP Simple Mail Transfer Protocol Protocol that transfers outgoing emails between servers from email clients to servers.
• POP Post Office Protocol Protocol that retrieves emails from a mail server and transfers them to the user device. By doing this the original email is deleted from the server.
• IMAP Internet Message Access Protocol Protocol that retrieves emails from a mail server and transfers them to the user device. After this process a copy of the email is kept on the server. This allows the user to access the email from multiple devices. (Synchronicity)
• Protocol Layering Divides complex tasks of networking into smaller simpler tasks that work in tandem with eachother.
• Advantages of Protocol Layering Reduces a complex problem into smaller sub-problems. (Decomposition) Devices can be manafactured to operate at a particular layer. Products from different manafactures can work together.
• TCP/IP Stack A step of 4 networking layers working together responsible for transmission of data packets.
• 4 Networking Layers

  
  

  Application Layer

  Transport Layer

  Internet Layer

  Link Layer
• Application Layer Interacts directly with software applications preparing data for transmission by converting it into a format that can be sent and recieved over the network. Web browsers and email applications operate at this layer.
• Transport Layer Responsible for end to end communication between the source and destination. Breaks the data into packets and assigns each packet a port number.
• Internet Layer Adds a header to each packet containing sender and reciever IP address. Responsible for routing each packet across the network using the IP addresses.
• Link Layer Network Interface Layer Recieves packets from internet layer and prepares them for transmission over the physical network. This layer translates digital packets into an electrical, optical or wireless signal that can be sent over the network.
• IP Address Unique identifier for a device on a network. Used to deliver packets to the correct destination.
• DNS Domain Name Server Translates human readable domain names to their corresponding IP addresses
• What happens during a search.

  
  

  URL Entry - User enters url into browser

  DNS Query - Browser sends query to DNS to translate the url into the corresponding IP address.

  DNS Resolver - If IP address is not found DNS sends query to another server.

  DNS returns the corresponding IP address of the webserver.

  Browser queries the webserver using the IP for the data needed to host the webpage.
• LAN Local Area Network A network that consists of multiple devices connected together within a small geographical location.
• WAN Wide Area Network Network consisting of multiple LANs connected together within a large geographical area.
• Advantages of LAN Security - LAN can secure its devices through the use of firewalls and antivirus software to prevent unauthorised access. Centralised Management - Allows for centralised management of updates and backups.
• Disadvantages of LANs If hardware fails the network will not function properly. Access to data can be slow depending on network traffic. LAN networks require maintenance to ensure software is up to date.
• Packet Switching Communication method that breaks down data into packets and routing them seperately along different routes.
• Advantages of Packet Switching Efficient use of network resources - packets follow different paths to the destination using the most available bandwidth. More reliable - If a packet fails to reach its destination only that packet needs to be resent. Lower cost - Network resources are shared.
• Disadvantages of Packet Switching Not ideal for real time services - These require a steady stream of data without delays. Packets can arrive out of order - This requires reassembly and error checking which takes time. Congestion - Network traffic can be high and cause congestion slowing the flow of packets.
• Circuit Switching Communication method where a dedicated communication path is established between two devices for the duration of their conversation. All packets are sent along the same route.
• Advantages of Circuit Switching Ideal for real time services - constant and steady rate of data transmission. No delays - A dedicated path is established each packet will be at its destination. Data arrives in order - Packets are not seperated and so arrive in order which does not need error checking or reassembly.
• Disadvantages of Circuit Switching Less efficient - Network resources remain allocated during the whole conversation. Expensive - Dedicated line requirement can be costly. Less scalable - Adding new devices can be complex.
• DOS attack Denial of Service A computer floods a server with many requests which causes it to crash
• SQL Injection Malicious SQL statements are inserted into an entry field for execution exposing a companys database to hackers.
• Phishing Attempt to gain sensitive information by pretending to be a trustworthy entity through electronic communication.
• Ways of preventing malware FirewallsAntivirus softwareSecure PasswordsEncryption softwareRegular software updates