• Communication Systems: a system that enables people to send and receive data and information (telephone, radio and television)
• Occurs between transmitter and receiver over a network and between nodes

Framework in which communication systems function, demonstrated by the following model:

• Basic Components of a communication system are:
  • Data Source: Produces the data to be sent. E.g. Person speaking into microphone
  • Transmitter: Encodes the data into a suitable signal for a transmission medium
    • Microphone and associated electronics (that allow the sound recorded to be collected and turned into signal to be sent)
  • Transmission medium: Channel in which the signal is transmitted to the destination.
    • The signal may be changed/distorted during transmission
    • Good communication systems have an accurate, reliable and secure transmission medium
      • E.g. Cables and wires that the signal travels through
  • Receiver: decodes the signal back into original data/approximation of the data. E.g. Radio that converts signal back to original sounds
  • Destination : receiver of the information. E.g. Person listening to radio
  • Switches/ Routers: Where addresses are attached and read so that the data packets are sent on the most suitable path to destination
• Three levels of protocol: are where packets of data are encoded/decoded to or from a suitable form for transmission.
  • Where it is applied and used or made
  • Where it is encoded/decoded
  • Where it is sent
• Good communication systems have an accurate, reliable and secure transmission medium, where good communication can depend on:
  • Protocols
  • Handshaking
  • Speed of transmission:
    • Bits per second/ Bit Rate (bps) → Maximum number of bits that can be transferred in one second
    • Baud Rate → Maximum number of data symbols/electrical signals that can be transmitted in one second.
      • As data signals can contain more than one bit of data, bit rate may be different. E.g. 1200baud might transmit 4800 bps
  • Error checking

The Functions Performed by Communication Systems

Functions message undergoes when transmitting between source and destination

Data packet → a Unit of data ; data is made into a single package that travels along a given network path

• Used in IP (Internet Protocol). Helps navigate the Web, and other networks. Have payload and headers that carry metadata (I.e. routing info, address of origin/destination).

• Message creation → When the user creates a message using an application (that will be used when passing messages)
  • E.g. Using email application to write email
• Organisation of packets at the interface between source and transmitter → When the message descends the three different levels of protocol and each level adds its own header and trailer that includes data such as:
  • Address of sender/receiver (application level)
  • Error checks (communication control and addressing level)
• Signal generation by the transmitter → When the transmitter changes the data into a form suitable for transmission down the specific medium. Generates the signal to be transmitted
• Transmission → Occurs as each part of the message is sent down the transmission medium
• Synchronising the exchange → when the clocks of the sender/receiver are synchronised so transfer of data can occur in real time and without error; Involves including a series of bits at the start of the message that is embedded between the data packets.
• Addressing and routing → giving the data packet their destination and the most suitable route to get to the destination. Each hardware element (switch, etc.) on the transfer path reads the address of the data packet and sends it on the next stage of its journey. Different data packets will likely take different routes to reach the destination. Addressing and routing the data packets to their destination
• Error detection and correction → error detection methods are added to the data packet to ensure the data received is accurate ( e.g. checksum, parity bit, CRC)
• Security and management → When messages have to be secured during transmission.
  • Password protection of access
  • SSL encrypts data during transmission

The Roles of Protocols in Communication