Chapter 2

• All devices are connected to the network using a network interface card (NIC)
• advantages of serial transmission

  1 simple and reliable

  2 used over distances

  3 errors reduced
• disadvantage of serial transmission it is slow
• 8 bits is 1 byte
• Advantage of parallel transmission is that it is fast
• Disadvantage parallel transmission

  1 less reliable

  2 data may be skewed

  3 suitable for only short distances
• Parallel data transmission


  Transmitting multiple bits simultaneously
• Serial data transmission


  Transmitting one bit at a time
• Serial Transmission

  • Economical
  • 1 bit per clock pulse
  • Slow
  • Used for long distances
  • Less risk of external interference
  • Data is synchronized
• Parallel Transmission

  • Expensive
  • 8 bits per clock pulse
  • Fast
  • Used for short distances
  • More risk of interference
  • Risk of data being skewed
• When transmission is over longer distances, there is a risk of data being skewed
• Simplex transmission

  One-way data flow
• Half-duplex transmission

  Data can flow in both directions, but not simultaneously
• Full-duplex transmission


  Data can flow in both directions simultaneously
• Simplex transmission


  The data flow between source and desination occurs in unly une direction
• Simplex transmission

  • The source can only send the data, and the destination can only receive the data
  • Example: keyboard sending input signals to the monitor
  • Example: radio broadcast - user can only receive radio signals from the radio station but cannot reply
• Half-Duplex transmission


  The data flow between source and receiver occurs in both directions, but in only one direction at a time
• Half-Duplex transmission


  • Walkie-talkie - a person can either speak or hear but not at the same time
• Full-Duplex transmission


  The data flow between source and destination can occur simultaneasly
• Full-Duplex transmission

  • Video call - two people can see and hear each other at the same time
  • Broadband internet connection - data may be both sent and received
• Synchronous Transmission


  Bits of a message are combined into frames that are transmitted on a regular basis, without downtime or separation between the characters. Transmission of bits is synchronized by timing signals controlled by clock systems built into each of the sender and receiver machines.
• Synchronous Connection

  • Provides higher flow rates than asynchronous connection
  • May have more errors because a large number of bits are transmitted
• Asynchronous Transmission

  Characters are transmitted irregularly, one character at a time. Time interval between two characters is random, so the beginning of a character can occur at any time. No clock system is used. Timing or synchronization is guaranteed using control bits (start and stop bits) or flags that indicate the beginning and end of each character.
• Asynchronous Transmissions


  • Simple and cheap since there is no need to add clock components to the communicating machines
  • Appropriate for applications where messages are generated at irregular intervals, such as in keyboard data entry
  • Disadvantage is the large quantity of bits used for synchronization, which are transmitted uniquely for timing control purposes and transport no useful information
• Parity bit is used as error control mechanism
• Address Bus - carries addresses from CPU to RAM, ROM or other device
• Data bus - carries data between CPU and memory or peripherals
• Address Bus - carries addresses from CPU to RAM, ROM or other device
• SECTIC


  Error-Detection Techniques
• Leaving Pol

  Describe the proceso involved in das ane
• There are many sethniques in detect data transmision errors
• Echo Check


  Echoing back transmitted data means sending die data back again, from destination to sourer. If the data set back is the same as the data sent initially then the latter has been delivent comctly. If the echoed data is incorret, then the original data is ream. This method bellective; however, is efficent see it requires data to be sent twice. In addition, this method is not diable boca, if an error occurs, there is no way of telling if the error ocnard when the data was sent the fint time or when the data was sent hack to be checked.
• Simple Parity Check

  The main idea behind this technique is to append a bit to each data unui sent, so that the total number of Is, including the appended hit (also known as a parity bit, is even or odd. If the total number of Is is even, it is called even parity. If the total number of 1s is odd, it is called odd pants The source and destination should agree on whether they will be wing odd or even parity balone data transmissies.
• If the w devices that a coenomanicating agree to use, for example, odd parity, then there must always be an odd number of Is. When the transmision begins the transmitting device counts the number of Is in each set of seven birs. If the mamber is ockl, it sets the purity hit to 0. If the ber is even, it sets the parity bit se L. Similarly, every lyse sent has an odd number of 1s. On the receiving side, if a byte is reed with an ewn mumber of s, then this implies that an error has occurred during transnusson, This error is reported, and the unit of data is on
• Parity bit

  • 0
• Even parity error detection

  Ineration of the process
• Even parity error detection

  1. Source

  2. Compute parity

  3. Transmit

  4. Compute parity

  5. Destination

  6. Accept data
• A parity check is effective only if one bit gets erroneously changed
• If two bits change, the parity will still change because it will remain as even or odd, and the check will not discover the error
• Even if an error is detected, it is impossible to tell exactly which bit had the error