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Data communication


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Data communication

  1. 1. Data Communication Flow Control by Md.Javedul Ferdous East West University
  2. 2. Flow Control Flow control is the process of managing the rate of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with data from transmitting node.
  3. 3. So why need it ?????
  4. 4. Prevent degradation and loss of efficiency due to overload Deadlock avoidance Fair allocation of resources among competing users Speed matching between the network and its attached users.
  5. 5. Type of ‘Flow Control’ • Stop-and-wait • Sliding Window
  6. 6. Stop-and-wait • Fundamental technique to provide reliable transfer under unreliable packet delivery system • simplest form of flow control • inefficiencies when sending longer transmissions
  7. 7. Stop-and-wait
  8. 8. Sliding Window • Technique for controlling transmitted data packets between two network computers where reliable and sequential delivery of data packets is required • • Best utilized when the buffer size is limited and pre-established. • Better Performance
  9. 9. Levels of Flow Control Hop Level Entry-to-Exit Level Network Access Level Transport Level
  10. 10. Hop Level Prevent store and forward buffer congestion and its consequences Maintain a smooth flow of traffic between two neighboring nodes In a computer network
  11. 11. Entry-to-Exit Level Implement as a protocol between the source and destination switch Protect the exit node from congestion
  12. 12. Network Access Level Throttle external inputs based on measurements of internal network congestion.
  13. 13. Transport Level Efficient and reliable transmission of messages within each user session and the efficient sharing of common network resources by several user sessions Events destination buffer congestion and overflow is known as transport level flow control
  14. 14. Problem of ‘Flow Control’ Can’t send too slow or too fast Too slow wastes time Too fast can lead to buffer overflow