networks

• Wired networks


  Networks identified by their use of physical wiring to connect devices
• Wired networks


  • Most often used for office networks or for devices that are unlikely to move as the cables limit the ability to move away from the connection point
• Wireless networks


  Networks that use radio waves to carry signals
• Wireless networks


  • Signals are limited in range - usually up to 50 metres
  • Subject to interference
  • Can be blocked by walls
  • Ideal for mobile devices as a device can connect to a network as long as it is in the range of a wireless access point (WAP)
• Bluetooth


  A form of wireless communication that enables different devices to connect
• Bluetooth


  • Works like a small private network between two devices, allowing them to share data and documents
  • Many modern devices incorporate Bluetooth
  • Often used to connect wireless devices such as a keyboard or a mouse to a computer, a speaker to a smartphone, a smartphone to a car's multimedia system
• Bluetooth transmission speed


  Often only up to 2 megabits per second
• Bluetooth provides a simple way of connecting devices
• Bluetooth is limited in transmission speed and range
• Encryption


  The process of disguising a message so that it cannot be understood by anyone but its intended recipient
• Encryption


  • Requires the use of a key
  • The key is secret as to how the message has been disguised
• Five facts about encryption


  • Encryption does not prevent someone from intercepting a message - instead it prevents them from being able to understand it
  • Unencrypted messages are referred to as plaintext messages. Encrypted messages are known as ciphertext
  • A simple method of encryption requires the use of a technique known as the Caesar cipher
  • To decrypt the message, the process is reversed
  • Although this is a good example of encryption, in real life much more complicated algorithms are used to encrypt messages
• Protocol


  A set of rules that governs transmission of data
• Protocols that govern addressing


  • Internet Protocol (IP) addressing
  • media access control (MAC) addressing
• IP Addressing


  When connected to a network each device is given a unique IP address
• IP address


  • 192.168.0.254
• Sending a message to another node

  1. Use the recipient node's address as the destination

  2. Switch on the network knows where the node with this address is and routes the message to it accordingly
• Static IP address


  A node given a static address always keeps the same address
• Dynamic IP address


  A node given a dynamic address has a different address assigned to it each time it connects to the network
• Dynamic host configuration protocol (DHCP)


  Method of assigning dynamic IP addresses
• IPv4 allows for up to 4.3 billion addresses to be used
• IPv4 has run out of addresses due to the huge increase in internet-enabled devices
• IPv6


  New version with eight sets of four-digit hexadecimal values, separated by colons, greatly increasing the number of possible addresses, to around 340 trillion, trillion, trillion
• MAC address


  Unique serial number assigned to each network interface controller (NIC)
• MAC address


  • 1A:5B:6H:98:78:35
• The MAC address is assigned by the NIC's manufacturer and cannot be changed
• Other common protocols


  • TCP/IP
  • HTTP and HTTPS
  • FTP
  • SMTP
  • POP and IMAP
• Layering


  Breaking up the sending of messages into separate components and activities, where each component handles a different part of the communication
• TCP/IP


  Transmission Control Protocol/Internet Protocol - enables communication over the internet
• TCP/IP model


  The model for layering in networking
• HTTP and HTTPS


  Hypertext Transfer Protocol - governs communication between a webserver and a client. HTTPS (secure) includes secure encryption to allow transactions to be made over the internet
• Layers in the TCP/IP model


  • Application layer
  • Transport layer
  • Network layer
  • Link layer
• FTP


  File Transfer Protocol - governs the transmission of files across a network and the internet
• SMTP


  Simple Mail Transfer Protocol - governs the sending of email over a network to a mail server
• Application layer


  Encodes/decodes the message in a form that is understood by the sender and the recipient
• POP and IMAP


  Post Office Protocol and Internet Message Access Protocol - govern retrieving emails from email servers. POP is an older implementation, largely replaced by IMAP
• Transport layer


  Breaks down the message into small chunks (packets), gives each packet a number and the total number of packets, allows the recipient to assemble the packets in the correct order and see if any are missing
• Network layer


  Adds the sender's IP address and that of the recipient, so the network knows where to send the message and where it came from
• Link layer


  Enables the transfer of packets between nodes on a network, and between one network and another
• Layering


  • Allows standards to be developed and adapted to new hardware and software over time
  • Different software packages (applications) may use the same transport, network and link layers but have their own application layer