Transmission of Data

Transmission of Data

1. Parallel

   • Uses
     • Computer Buses
     • HDMI cable
     • Computer to display cable
     • Short printer cables
   • Paralell transmission is sending data over a number of lines at once. It is very fast but suffers more from noise and it is difficult to synchronise parallel lines over longer distances so is typically only used over very short distances

2. Serial

   • Serial transmission only requires one transmission line.
   • 1 Bit is only sent over at a time
   • Serial transmission is much more common than parallel over anything but very short distances
   • Although serial transmission only transmits data 1 bit at a time rather than 8, 16, 24, 32 or even 64 it is much cheaper to implement than parallel. It is able to be used over much longer runs than parallel transmission without error and thus can be pushed a good deal faster over more than very short distances

3. Sychronous

   • For Synchronous transmission the speed of transmission is synchronised with a clock signal on a sperate wire. Almost all parallel communication is synchronous. It can be very fast.
   • Does not stop and start transmission

4. Asynchronous

   • Asynchronous communication is more flexible as it only needs to be synced when transmitting. Each word includes a start bit to signal the start
   • Stops and starts transmission to sample the data at every clock pulse on the control bus

5. Handshaking

   • Handshaking is the first part of communication between two devices.
   • It is the process by which two communication devices agree the protocols they will use to communicate.
     • Speed they can both work at (bit per second)
     • synchronous or asynchronous
     • half duplex or full duplex
     • Error handling (parity)
     • Compression

6. Protocols

   • A protocol is a set of rules used by two devices to allow them to communicate.
   • Types of protocols on the internet
     • TCP - Controls how data is transmitted
     • FTP - Controls how files are uploaded/downloaded/moved
     • HTTP - Controls how webpages are handled
     • HTTPS - Controls how secure webpages, such as for e-commerce, are handled

7. Physical protocols

   • Physical protocols ensure that it is possible for two devices to communicate.
   • Examples
     • wired v wireless
     • CAT 6
     • Microwave
     • Fibre optic

8. Packet Switching

   • Packets can be sent over the network using whichever route is free. The packets usually contain a sequence number so that the packets can be reassembled in order at the destination
   • Different packets can take entirely different routes through a network from point A to point B

9. Virtual circuit

   • An ideal circuit which there is packet order and no packet loss. This is a virtual circuit

10. Sending and receiving packets

    • Packets are sent in order, but are received in any order
    • Example
      • A sentence could be split up in 3 pieces and the packets are sent off in order. lets say the sentence is "This is" "A" "Sentence" and they get sent off at the same time and when the packet is received the sentence order is "A" "Sentence" "This is" it will then organise this sentence when it is recieved using the sequence in the header as packets have a sequence number to display which way they are displayed

11. packets

    • A network packet is the unit of data transmitted in a packet-switched network. It is also sometimes called a datagram. It is typically about 1-2 kilobytes
    • Parts of a packet
      • Trailer
        • Contains the checksum which is a form of error handling.
        • Control information
      • Payload
        • Contains all the user data of the packet
      • Header
        • Control information
        • Contains source and destination and sequence number

12. Logical protocols

    • Logical protocols specify the format of the data and control bits, the packet size and format, compressiion and encrypton