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Communication Networks NETW 501

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Presentation on theme: "Communication Networks NETW 501"— Presentation transcript:

1 Communication Networks NETW 501
Lecture 9 Data Link Layer: Error Control & Flow Control Course Instructor: Dr.-Ing. Maggie Mashaly C3.220

2 Selective Repeat ARQ Protocol

3 Selective Repeat ARQ Basics
What is the problem of Go-Back N? Go Back-N retransmits the erroneous frame and all subsequent frames This reduces efficiency especially for High Error Channels Selective Repeat ARQ Introduce a receive window to store CORRECT out of sequence frames Retransmit individual frames TCP uses a form of selective repeat

4 Error Recovery in Selective Repeat ARQ
Receiver Sender Fr_0 ACK_1 Fr_1 ACK_2 Fr_2 Fr_3 Fr_4 NAK_2 ACK_2 Fr_2 ACK_5 Fr_5 ACK_6

5 Operation of Selective Repeat
WS=WR=2 , m=2 Receiver Sender Fr_0 Sending Window Fr_1 Receiving Window NAK_0 Fr_0 Fr_0 Fr_0 Fr_1 Fr_1 ACK_2 Fr_2 Fr_3 ACK_3 ACK_0 Frame Sequences that are allowed to be sent Frame Sequences that are allowed to be received Outstanding Frame Sequences Frame Sequences that are received correctly and buffered

6 Operation of Selective Repeat
WS=WR=2 , m=2 Receiver Sender Fr_0 Sending Window Fr_1 Receiving Window NAK_0 Fr_0 Fr_0 Fr_0 Fr_1 Fr_1 ACK_2 Fr_2 Fr_3 ACK_3 ACK_0 Frame Sequences that are allowed to be sent Frame Sequences that are allowed to be received Outstanding Frame Sequences Frame Sequences that are received correctly and buffered

7 Operation of Selective Repeat
WS=WR=2 , m=2 Receiver Sender Fr_0 Sending Window Fr_1 Receiving Window NAK_0 Fr_0 Fr_0 Fr_0 Fr_1 Fr_1 ACK_2 Fr_2 Fr_3 ACK_3 ACK_0 Frame Sequences that are allowed to be sent Frame Sequences that are allowed to be received Outstanding Frame Sequences Frame Sequences that are received correctly and buffered

8 Operation of Selective Repeat
WS=WR=2 , m=2 Receiver Sender Fr_0 Sending Window Fr_1 Receiving Window NAK_0 Fr_0 Fr_0 Fr_0 Fr_1 Fr_1 ACK_2 Fr_2 Fr_3 ACK_3 ACK_0 Frame Sequences that are allowed to be sent Frame Sequences that are allowed to be received Outstanding Frame Sequences Frame Sequences that are received correctly and buffered

9 Operation of Selective Repeat
WS=WR=2 , m=2 Receiver Sender Fr_0 Sending Window Fr_1 Receiving Window NAK_0 Fr_0 Fr_0 Fr_0 Fr_1 Fr_1 ACK_2 Fr_2 Fr_3 ACK_3 ACK_0 Frame Sequences that are allowed to be sent Frame Sequences that are allowed to be received Outstanding Frame Sequences Frame Sequences that are received correctly and buffered

10 Operation of Selective Repeat
WS=WR=2 , m=2 Receiver Sender Fr_0 Sending Window Fr_1 Receiving Window NAK_0 Fr_0 Fr_2 Fr_0 Fr_1 Fr_3 ACK_2 Fr_2 Fr_3 ACK_3 ACK_0 Frame Sequences that are allowed to be sent Frame Sequences that are allowed to be received Outstanding Frame Sequences Frame Sequences that are received correctly and buffered

11 Operation of Selective Repeat
WS=WR=2 , m=2 Receiver Sender Fr_0 Sending Window Fr_1 Receiving Window NAK_0 Fr_2 Fr_2 Fr_0 Fr_3 Fr_3 ACK_2 Fr_2 Fr_3 ACK_3 ACK_0 Frame Sequences that are allowed to be sent Frame Sequences that are allowed to be received Outstanding Frame Sequences Frame Sequences that are received correctly and buffered

12 Operation of Selective Repeat
WS=WR=2 , m=2 Receiver Sender Fr_0 Sending Window Fr_1 Receiving Window NAK_0 Fr_2 Fr_2 Fr_0 Fr_3 Fr_3 ACK_2 Fr_2 Fr_3 ACK_3 ACK_0 Frame Sequences that are allowed to be sent Frame Sequences that are allowed to be received Outstanding Frame Sequences Frame Sequences that are received correctly and buffered

13 Operation of Selective Repeat
WS=WR=2 , m=2 Receiver Sender Fr_0 Sending Window Fr_1 Receiving Window NAK_0 Fr_2 Fr_3 Fr_0 Fr_3 Fr_0 ACK_2 Fr_2 Fr_3 ACK_3 ACK_0 Frame Sequences that are allowed to be sent Frame Sequences that are allowed to be received Outstanding Frame Sequences Frame Sequences that are received correctly and buffered

14 Operation of Selective Repeat
WS=WR=2 , m=2 Receiver Sender Fr_0 Sending Window Fr_1 Receiving Window NAK_0 Fr_2 Fr_3 Fr_0 Fr_3 Fr_0 ACK_2 Fr_2 Fr_3 ACK_3 ACK_0 Frame Sequences that are allowed to be sent Frame Sequences that are allowed to be received Outstanding Frame Sequences Frame Sequences that are received correctly and buffered

15 Send and Receive Window Size
m=2 WS=WR=3 WS=WR=2 Receiver Receiver Sender Sender Fr_0 Fr_0 ACK_1 ACK_1 Fr_1 Fr_1 ACK_2 ACK_0 Fr_2 Fr_0 Receive Window {2,3} Fr_0 ACK_3 Fr_0 rejected Receive Window {3,0,1} GENERAL RULE: WS+ WR ≤2m

16 Efficiency Plots Frame Size 1024, R=1.5 Mbps, tprop=5 ms, Window Size = 4

17 References NETW 501 Lectures slides by Assoc. Prof. Tallal El-Shabrawy
“Communication Networks 2nd Edition”, A. Leon-Garcia and I. Widjaja, McGraw Hill, 2013 “Computer Networks 4th Edition”, A. S. Tanenbaum, Pearson International

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