2.1 Types and methods of data transmission

## Types and Methods of Data Transmission

### Data Packets
- #### Packet Structure
  - Header
    - Contains the IP address of the sender and the receiver
    - The sequence number of the packet
    - Size of the packet
  - Payload
    - Contains the actual data
  - Trailer
    - Includes a method of identifying the end of the packet
    - Error-Checking methods
- #### Packet Switching
  - Data is broken/split/divided into packets
  - Each packet (could) take a different route
  - A router controls the route/path a packet takes selecting the shortest/fastest available route/path
  - Packets may arrive out of order
  - Once the last packet has arrived, packets are reordered
  - If a packet is missing/corrupted, it is requested again

| Advantages                                       | Disadvantages                                                |
| ------------------------------------------------ | ------------------------------------------------------------ |
| No need to create a single line of communication | Packets may be lost                                          |
| Possible to overcome failed or busy nodes        | More prone to errors in real-time streaming                  |
| High data transmission speed                     | Delay at the receiver while the packets are being re-ordered |
| Easy to expand package usage                     |                                                              |

### Data Transmission

- *Simplex data transmission* is in one direction only (e.g. computer to printer)
- *Half-duplex data transmission* is in both directions but not at the same time (e.g., in a phone conversation where only one person speaks)
- *Full-duplex data transmission* is in both directions simultaneously (e.g. broadband connection on the phone line)
- *Serial data transmission* is when data is sent one bit at a time over a single wire
- *Parallel data transmission* is when data of several bits (1 byte) are sent down several wires at the same time.

### **Comparison of Serial and Parallel Data Transmission**

| Serial                                          | Parallel                                       |
| ----------------------------------------------- | ---------------------------------------------- |
| Better for longer distances (Telephone Lines)   | Better for short distances (Internal circuits) |
| Cheaper Option                                  | Expensive (More hardware required)             |
| Used when the size of data transmitted is small | Used when speed is necessary                   |
| Slower Option                                   | Faster than Serial                             |

## Universal Serial Bus (USB)

- USB is an asynchronous serial data transmission method
- USB consists of:
  - Four-wire shielded cable
  - Two wires are used for power and earth
  - Two wires are used in data transmission

| Advantages                                       | Disadvantages                             |
| ------------------------------------------------ | ----------------------------------------- |
| Automatically detected                           | Transmission rate is less than 120 MB/sec |
| Only fit one way, prevents incorrect connections | Maximum cable length is about 5 metres    |
| Different data transmission rates                |                                           |
| Backwards compatible                             |                                           |
| Industry-standard                                |                                           |