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SESSION 7,8- SLIDOP WINDOW,STOP AND WAIT.ppt

SESSION 7,8- SLIDOP WINDOW,STOP AND WAIT.ppt - PROTOCOLS...

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PROTOCOLS PROTOCOLS COMPUTER NETWORKS © KLU TEAM
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Our first protocol is a simple protocol with neither flow nor error control. We assume that the receiver can immediately handle any frame it receives. Simple Protocol COMPUTER NETWORKS © KLU TEAM
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Simple Protocol COMPUTER NETWORKS © KLU TEAM
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Simple Protocol Flow Diagram COMPUTER NETWORKS © KLU TEAM
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Our second protocol is called the Stop-and-Wait protocol, which uses both flow and error control. In this protocol, the sender sends one frame at a time and waits for an acknowledgment before sending the next one. To detect corrupted frames, we need to add a CRC to each data frame. When a frame arrives at the receiver site, it is checked. If its CRC is incorrect, the frame is corrupted and silently discarded. Stop & Wait Protocol COMPUTER NETWORKS © KLU TEAM
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The silence of the receiver is a signal for the sender that a frame was either corrupted or lost. Every time the sender sends a frame, it starts a timer. If an acknowledgment arrives before the timer expires, the timer is stopped and the sender sends the next frame (if it has one to send). If the timer expires, the sender resends the previous frame, assuming that the frame was either lost or corrupted. Stop & Wait Protocol COMPUTER NETWORKS © KLU TEAM
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This means that the sender needs to keep a copy of the frame until its acknowledgment arrives. When the corresponding acknowledgment arrives, the sender discards the copy and sends the next frame if it is ready. Stop & Wait Protocol COMPUTER NETWORKS © KLU TEAM
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Stop & Wait Protocol COMPUTER NETWORKS © KLU TEAM
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1. The ACK is received before the timer expires 1. The original frame is lost 2. The ACK is lost 3. The timeout fires too soon. Stop & Wait Protocol COMPUTER NETWORKS © KLU TEAM
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We need to add sequence numbers to the data frames and a cknowledgment numbers to the ACK frames. However, numbering in this case is very simple. Sequence numbers are 0, 1, 0, 1, 0, 1, . . . ; the acknowledgment numbers can also be 1, 0, 1, 0, 1, 0, … In other words, the sequence numbers start with 0, the acknowledgment numbers start with 1. An acknowledgment number always defines the sequence number of the next frame to receive. Stop & Wait Protocol COMPUTER NETWORKS © KLU TEAM
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Stop & Wait Protocol Normal Operation COMPUTER NETWORKS © KLU TEAM
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Stop & Wait ARQ, Lost frame COMPUTER NETWORKS © KLU TEAM
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Stop & Wait ARQ, Lost ACK frame COMPUTER NETWORKS © KLU TEAM
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Stop & Wait ARQ, Delayed ACK frame COMPUTER NETWORKS © KLU TEAM
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Stop & Wait Protocol COMPUTER NETWORKS © KLU TEAM
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Stop & Wait Protocol COMPUTER NETWORKS © KLU TEAM
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Stop & Wait Protocol COMPUTER NETWORKS © KLU TEAM
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In stop-and-wait, at any point in time, there is only one frame that is sent and waiting to be acknowledged.
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