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132B_1_Recitation5_ARQ_Schemes

132B_1_Recitation5_ARQ_Schemes - EE132B Recitation 5 ARQ...

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EE132B - Recitation 5 ARQ Schemes Prof. Izhak Rubin [email protected] Electrical Engineering Department UCLA 1
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ARQ Schemes Various Schemes: Stop and Wait Go back N Selective Repeat Example: we send a total of 6 packets For Go Back N, use N = 3 P e = 0.25 (for simplicity, assume every fourth packet has an error). 2
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Stop and Wait Half duplex It is important to number the packet and ACK PKT 1 ACK 1 PKT 3 ACK 3 transmitter receiver Send PKT 1 Time expires PKT 2 ACK 2 PKT 4 (error) PKT 4 ACK 4 PKT 5 ACK 5 PKT 6 ACK 6 3
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Go back N Full duplex Pipelining Ensure the oldest frame transmitted successfully 1 ACK 1 transmitter receiver Time expires 2 3 ACK 2 ACK 3 4 5 6 Ignored by receiver (out of sequence packets) 4 5 6 ACK 4 5 6 ACK 5 ACK 6 4
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