Networks

Networks

1. The Internet

   • Worldwide connection of inter-connected networks
   • No-one owns it and everyone can access it
   • Websites are stored on web servers connected to the internet
   • Info on the WWW is accessed using a web browser

2. Domain Names

   • Easy to remember
   • DNS server translates the domain name into an IP address
   • Humans do not have to remember the IP address
   • If IP address changes, the DNS servers can keep their domain name

3. MAC addressing

   • NIC's allow devices to connect to the internet
   • All NIC's have a MAC address assigned to it.
   • MAC addresses are 48 bits long (12 hex digits)

4. WAN's

   • The Internet is the largest WAN
   • Spread over a large geographical area
   • Cables, telephone lines, satellites, and radio waves connect the components

5. Circuit Switching and Packet Switching

   • When calling someone, the connection between you and the receiver is called circuit switching
   • As there are not enough lines for people sending data, packet switching is needed
   • If a 3MB file is sent across the internet, the file is broken into 'packets' of around 512 bytes
   • Each packet contains: IP address it is going to, IP address it has come from, sequence number of packets, number of packets needed and error checking data
   • Packets are sent along different routes and reassembled at its destination

6. LAN's

   • Covers a small geographical area
   • Collection of computers and peripheral devices connected together
   • Often owned by a person or small organisation

7. Star Topology

   • Failure of one node does not affect the whole network
   • Easy to expand
   • Performance is dependent on the central device
   • Expensive
   • If the central device fails, everything fails

8. Mesh Topologies

   • Failure of one node does not affect the whole network
   • Data can be transmitted simultaneously
   • Expansion and modification is easy
   • Expensive
   • Lots of cabling
   • Maintenance is difficult

9. Network Hardware

   • NIC's
     • Any device that can connect to a network has a NIC
     • Can be wired or wireless in order to connect to the Internet
   • Ethernet
     • Refers to a family of networking rules or protocols primarily used in LAN's
     • Divides data into frames
     • Faulty frames are dropped
   • Routers guide packets across a WAN
   • Switches know the MAC addresses of each device

10. Virtual Networks

    • Subset of computers connected together as part of a larger network
    • Computers act a a smaller, private network
    • A Virtual Private Network (VPN), is set up when an employee of a company in a remote area needs to connect to the company's private network
    • Communications need to be encrypted as there is risk of hacking

11. Wi-Fi frequency and channels

    • 2.4GHz
      • Greater range and coverage
      • More interference from other devices, and only three non-overlapping channels
    • 5GHz
      • Less crowded space with 23 non-overlapping channels and higher data transmission rates
      • Fewer devices can use the 5GHz frequency, less able to penetrate through walls.

12. Encryption

    • Secures data by scrambling the information
    • Encyrption denies hackers to be able to delete, add and modify confidential data
    • Plaintext - original message to be encrypted
    • Cipher text - the encrypted message
    • Encryption - the process of converting plaintext into cipher text
    • Key - a sequence of numbers used to encrypt or decrypt, often using a mathematical formula
    • The two types of encryption are: symmetric and asymmetric

13. Client-server and P2P networks

    • Client-Server
      • Central backing store is available to all computers
      • Security controlled by the central computer
      • Backup done centrally
      • Users reliant on the central server
      • Can support hundreds of users and can constantly grow
    • P2P
      • Storage facilities are distributed across all computers
      • Security is not centrally controlled
      • Backup done separately
      • No central server
      • Easy to set up but suited to homes and small businesses

14. Protocols

    • TCP/IP
      • TCP defines how messages are broken up and reassembled again
      • IP identifies the location of a device on the Internet and routes the packets there
    • HTTP/HTTPS
      • HTTP is used for accessing and receiving web pages in the HTML form
      • HTTPS encrypts the information so it cannot be understood if it is hacked,
    • FTP
      • File Transfer Protocol transfers files between a client and a server
    • POP
      • Receives and holds emails
      • Creates local copies of emails and deletes the original
      • Works best with one computer
    • IMAP
      • Stores email messages onto a server
      • Allows users to view and manipulate messages
      • Allows simultaneous access between files
      • Multiple computers can be used to check email
    • SMTP
      • Sends messages between servers
      • SMTP typically used for sending emails whereas POP and IMAP are used for receiving emails.

15. Concept of Layers

    • Application Layer
      • Encodes the data so it will be understandable to the recipient
    • Transport Layer
      • Splits the data into packets
      • Adds extra info like packet numbers so it can be reassembled quickly
    • Network/Internet Layer
      • Attaches IP address of the sender so the recipient knows who sent it
      • Attaches the IP address of the host and the destination IP address
    • Link Layer
      • Attaches the MAC addresses of the sender and the recipient, allowing the packet to be directed to a specific device on a LAN