Presentation on Flow Control (noisy and non-noisy channels))
- 1. PRESENTATION ON FLOW CONTROL Anubhav Mishra E219 Shashank E204 Vivek Kumar E205 Ujjwal Sen E203
- 2. WHAT IS FLOW CONTROL? Flow control in computer networks is defined as the process of managing the rate of transmission of data between two systems
- 3. CLASSIFICATION OF FLOW CONTROL FLOW CONTROL PROTOCOLS FOR NON NOISY CHANNELS STOP & WAIT FOR NOISY CHANNELS STOP & WAIT ARQ GO BACK N ARQ SELECTIVE REPEAT ARQ
- 4. STOP AND WAIT PROTOCOL The Stop-and-Wait Protocol is a simple method used for reliable data transmission. It ensures that data frames are transmitted correctly, one at a time, by waiting for an acknowledgment before sending the next frame.
- 5. STOP AND WAIT PROTOCOL Receiver Sender Data Data Data Acknowledgment Acknowledgment Acknowledgment
- 6. PROBLEMS IN STOP AND WAIT PROBLEM 1: LOST DATA Receiver Sender Data X Sender waits infinite time for acknowledgement
- 7. STOP AND WAIT ARQ (AUTOMATIC REPEAT REQUEST) In STOP and WAIT ARQ, the sender is able to transmit data without receiving acknowledgment. It is a sliding window protocol with size of window = 1 It solves the problem of STOP and WAIT
- 8. SOLUTIONS USING STOP AND WAIT ARQ SOLUTION 1: TIME OUT TIMER Receiver Sender Data X Data Acknowledgement Time out timer
- 9. PROBLEMS IN STOP AND WAIT PROBLEM 2: LOST ACKNOWLEDGMENT Receiver Sender Data Data Acknowledgement Same data packet is sent 2 times X Ack
- 10. SOLUTIONS USING STOP AND WAIT ARQ SOLUTION 2: PUTTING SEQUENCE NUMBER ON DATA PACKETS Receiver Sender Data-p1 Data-p1 Acknowledgement X Ack
- 11. PROBLEMS IN STOP AND WAIT PROBLEM 3: DELAYED ACKNOWLEDGEMENT Receiver Sender Data-p1 Data-p1 Ack X Ack Delayed Ack
- 12. SOLUTIONS USING STOP AND WAIT ARQ SOLUTION 3: PUTTING SEQUENCE NUMBER ON ACKNOWLEDGEMENT Receiver Sender Data-p1 Data-p1 Discards duplicate packet and then resends acknowledgement-1 X Ack-1 Delayed Ack Ack-1
- 13. LIMITATIONS OF STOP AND WAIT ARQ Inefficient Utilization of Bandwidth: Only one frame is sent at a time, and the sender must wait for an acknowledgment before sending the next frame. This causes underutilization of the available bandwidth, especially on high-latency networks. High Latency: The protocol introduces high delays, as the sender must wait for each acknowledgment before proceeding, making it unsuitable for networks with long propagation delays. Idle Sender: The sender remains idle after sending each
- 14. GO BACK-N ARQ Go-Back-N ARQ (Automatic Repeat Request) is a data link layer protocol used for reliable data transmission, improving on the limitations of the Stop-and-Wait ARQ. In Go-Back-N, multiple frames can be sent without waiting for individual acknowledgments, which allows better utilization of network bandwidth.
- 15. GO BACK-N ARQ Receiver Sender 1 1 2 3 4 5 6 7 Sliding Window Window Size: 3 2 3 4 Packet Lost: 5th 1 2 3 4 5 6 7 5 X 1 2 X X X 5 6 7 3 4 5 X X 7 1
- 16. LIMITATIONS OF GO BACK-N ARQ Redundant Retransmissions: If a single frame is lost or corrupted, Go-Back-N requires the sender to retransmit not only the lost frame but also all subsequent frames, even if those frames were received correctly by the receiver. This leads to inefficient use of bandwidth, especially when errors are rare. Increased Delay Due to Errors: When errors occur, retransmitting a large number of frames (because the entire window may need to be retransmitted) can cause delays in the network, leading to higher latency in the
- 17. SELECTIVE REPEAT ARQ Selective Repeat ARQ (Automatic Repeat Request) is a reliable data transmission protocol that overcomes the limitations of both Stop-and-Wait ARQ and Go-Back-N ARQ. It allows the sender to send multiple frames at a time, similar to Go-Back- N, but it only retransmits frames that were received with errors or were lost, instead of retransmitting all subsequent frames.
- 19. ADVANTAGES OF SELECTIVE REPEAT ARQ Efficient Use of Bandwidth: Only the frames that were lost or corrupted are retransmitted, rather than all subsequent frames. This significantly reduces redundant retransmissions and makes better use of network bandwidth, especially in error-prone environments. Minimizes Delays: Selective Repeat minimizes the delays caused by retransmissions since only the erroneous or lost frames are retransmitted. This improves overall performance, especially in
- 20. LIMITATIONS OF SELECTIVE REPEAT ARQ Increased Complexity: Selective Repeat requires both the sender and receiver to maintain separate buffers to store out-of-order frames. This adds to the complexity of the protocol compared to simpler mechanisms like Stop-and-Wait or Go-Back-N ARQ. Larger Buffer Requirement: Since the receiver can accept and store out-of-order frames until missing ones are retransmitted, it needs sufficient buffer memory to hold these frames. This increases the hardware or memory overhead, especially for high-window sizes. More Complex Window Management: Both the sender and receiver must keep track of individual frame acknowledgments, making the sliding window management more complicated. Each frame has to be tracked separately, as opposed to cumulative acknowledgments in Go-
- 21. THANK YOU!!! Anubhav Mishra E219 Shashank E204 Vivek Kumar E205 Ujjwal Sen E203
Editor's Notes
- #9: Same data packet is sent again