414Lecture7

414Lecture7 - Lecture 7 Transport Layer Reliable data...

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Lecture 7 Transport Layer Reliable data transfer, Stop-and-Wait ARQ, Go-Back-N ECSE 414 – Fall 2010
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ECSE 414, Lecture 7 2 Announcements Project topics Homework Assignment #1 Due now Homework Assignment #2 Will be posted soon 2010 Michael Rabbat
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Transport Layer Issues Characteristics of an unreliable data channel Bit errors Dropped packets Delayed packets Goal: Deal with these issues without too much added complexity ACK/NAK Sequence numbers Timers ECSE 414, Lecture 7 3 2010 Michael Rabbat
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ECSE 414, Lecture 7 4 Stop-and-wait protocols Only one unacknowledged packet allowed in flight. acknowledgements (ACKs): receiver explicitly tells sender that packet was received successfully Sender waits until it receives confirmation of correct receipt before sending the next packet. 2010 Michael Rabbat
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ECSE 414, Lecture 7 5 Stop-and-wait Transport Transport Layer needs to handle: Transmission errors In-order delivery Dropped packets Stop-and-Wait ARQ Automatic Repeat reQuest “Repeat request” is implicit in absence of ACK 2010 Michael Rabbat
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ECSE 414, Lecture 7 6 Stop-and-Wait ARQ Ideal (drop-free, error-free) operation: Sender transmits Receiver responds with an ACK No NAKs in this version Instead of NAK, send ACK for previous sequence number Sequence numbers (SNs) to keep sender and receiver synchronized Remarks: Only need one bit for sequence number Sender and receiver only need two states (one bit each) Sender is proactive (transmits and retransmits) Receiver is reactive (only responds to received packets) 2010 Michael Rabbat
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ECSE 414, Lecture 7 7 Stop-and-Wait Sender Means trying to send packet with SN=0 After sending a packet with SN= Sender State : If (ACK is error-free and SN= Sender State ) Increment Sender State
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This note was uploaded on 05/09/2011 for the course ECSE 414 taught by Professor Rabbat during the Fall '10 term at McGill.

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414Lecture7 - Lecture 7 Transport Layer Reliable data...

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