Data transmission

• Packets


  Small chunks of information/data that information on the internet is broken down into and created by TCP for transmission over the internet
• TCP (Transmission Control Protocol)

  Used for organizing data transmission over networks
• Small chunks of data are easier and quicker to route over the internet than big chunks of data
• Routing involves finding the most optimal path over a network
• Packet header

  Contains source IP, destination IP, packet number, and error checker
• Packet payload


  The actual data
• Packet trailer


  Contains additional error checks and end of packet notification
• Error checks make sure that when a packet is received there is minimal or no corruption of the data
• Parity bit

  Checks that no bits have been flipped from 0 to 1 or vice versa
• Checksum

  Performs a calculation and compares the result to the checksum value to check for data corruption
• Packet switching

  The process of sending packets over the internet, which is more efficient than circuit switching
• Packet switching


  • Routers know which nearby router is closer to the destination device
  • Packets from the same message can take different routes from the sender to the receiver, and may arrive in different orders
  • The receiver's computer reassembles the message by reordering the packets using the packet numbers
• Routing table

  Keeps track of nearby routers like a map or contacts list
• If a packet does not reach its destination the receiver can send a resend request to the sender to resend the packet
• Advantages of packet switching

  • Interference and corruption are minimal as individual packets can be resent if they are lost or damaged
  • The whole file doesn't need to be resent if a corruption occurs, only the individual packets that were corrupted need to be resent
  • Packet switching is quicker than sending a large packet as each packet finds the quickest way around the network
  • It's harder to hack an individual's data as each packet contains minimal data, and travels through the network separately
• Sending an email using packet switching

  1. Email is broken down into packets

  2. Each packet receives a source address, destination address, and packet number

  3. Each packet receives an error check like a parity bit

  4. Packets are sent over the internet via routers

  5. Packets may take different routes and arrive in any order

  6. Packets are checked for errors and missing packets can be requested to be resent

  7. Once all packets are received they are put together in order using the packet numbers
• Serial transmission


  One bit is sent at a time across a single wire
• Parallel transmission

  Multiple bits are sent at a time across several wires, but transmission is asynchronous as some bits may arrive quicker than others
• Simplex transmission


  Unidirectional, data travels in only one direction
• Half-duplex transmission


  Bidirectional, but data cannot be transmitted in both directions simultaneously
• Full-duplex transmission


  Bidirectional, data can be transmitted in both directions at the same time
• Wire types


  • Serial-Simplex
  • Serial-Half-duplex
  • Serial-Full-duplex
  • Parallel-Simplex
  • Parallel-Half-duplex
  • Parallel-Full-duplex
• Serial-Simplex

  Data is transmitted one bit at a time in a single direction on one wire
• Serial-Half-duplex

  Data can be transmitted in both directions on a single wire but only one bit at a time can be transmitted in one direction at a time
• Serial-Full-duplex


  Data can be transmitted in both directions at the same time on a single wire one bit at a time
• Parallel-Simplex


  Multiple wires transmit one bit at a time in one direction
• Parallel-Half-duplex


  Multiple wires send multiple bits of data in both directions but only one direction at a time
• Parallel-Full-duplex

  Multiple wires send multiple bits of data in both directions at the same time
• Advantages of serial transmission

  • The data will arrive in the order it is sent
  • It is less likely to have errors
  • Serial transmission is cheap over short and long distances as the cost of wire is fairly inexpensive
• Disadvantages of serial transmission

  • Data transmission is slow, especially over long distances as only small quantities of data can be transmitted at a time
• Advantages of serial transmission

  • The data will arrive in the order it is sent
  • It is less likely to have errors
  • Serial transmission is cheap over short and long distances as the cost of wire is fairly inexpensive
• Disadvantages of serial transmission

  • Data transmission is slow, especially over long distances as only small quantities of data can be transmitted at a time
  • Serial transmission is expensive over very long distances as the cost of wire dramatically increases
• Advantages of parallel transmission

  • Parallel transmission is fast as large quantities of data can be transmitted at any one time
• Disadvantages of parallel transmission

  • Parallel transmission is expensive over short distances as multiple wires need to be purchased
  • Transmission is very expensive over long distances as the cost of wires dramatically increases with the distance
  • Delays can be caused if data arrives asynchronously as the receiver has to wait for all of the bits before accepting new data
  • Buyers may be used to store data temporarily while waiting for all bits to arrive
• Advantages of simplex transmission

  • Simplex wires are cheap as only one wire is used
• Disadvantages of simplex transmission

  • Data transmission is slow as data still travels one bit at a time in only one direction at a time
  • Simplex transmission requires two sets of wires for bidirectional transmission meaning it can become expensive
• Advantages of half-duplex transmission

  • Half-duplex transmission is cheaper than simplex for bidirectional transmission as it requires fewer wires
• Disadvantages of half-duplex transmission

  • Transmission is still slow as data travels one bit at a time in only one direction at a time
• Advantages of full-duplex transmission

  • Full-duplex transmission is faster as data can travel in both directions simultaneously
  • The receiver does not have to wait for the sender to stop before they can start transmitting their data
• Disadvantages of full-duplex transmission

  • Full-duplex is expensive as the wire technology to transmit in both directions is more difficult to implement