Lecture19_2up

Lecture19_2up - ECE-547 Introduction to Computer...

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1 Purdue University ECE ECE -547 547 Introduction to Computer Introduction to Computer Communication Networks Communication Networks Instructor: Instructor: Xiaojun Xiaojun Lin Lin Lecture Lecture 19 19 Purdue University Go Back N Go Back N ¾ Go-back-N Protocol ± Data frames are Xmitted continuously without waiting for an Ack ± On receipt of a Nack or time out the frame is retransmitted and all frames following it are also transmitted
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2 Purdue University Go back n Protocol Go back n Protocol ¾ Example: A1 A2 A5 A3 A4 A6 A3 A4 A5 Ack A1 Ack A2 Nack A3 or timeout occurs Station A Station B ¾ We expect Go-Back-N to outperform stop and wait. ¾ Note: In practical applications, often not all packets are acked. An Ack may positively Ack all frames preceding it Purdue University Selective Repeat Protocol Selective Repeat Protocol ¾ Selective Repeat: In this case, only the frame that is Nacked or the frame for which time out has occurred needs to be retransmitted ¾ A reordering buffer is required at the receiver since frames may be Xmitted out of order
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Lecture19_2up - ECE-547 Introduction to Computer...

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