1. COMMUNICATION NETWORKS NETW 501 TUTORIAL 9 Presented by: Eng. Hana Hesham Eng. Mohamed Atef

2. Sheet 8 – Problem 3  Consider a link that uses Selective Repeat ARQ with a sending window size of WS=4 and receiving window size WR = 2. Suppose that frames use a time-out value of 3 units. Also, assume that ACK transmission time and the processing time are negligible. Figure (1) shows the operation of the ARQ protocol during the sending of M frames.

3. Sheet 8 – Problem 3  What is the minimum number of bits that should be used for sequencing?

4. Sheet 8 – Problem 3 Insert the appropriate frames & ACKs numbers in the gray boxes in figure (1).

5. Efficiency of Stop and Wait

6. Efficiency of Stop and Wait in Error Free Channel

7. Efficiency of Stop and Wait in Channel with Error

8. Efficiency of Go Back N

9. Efficiency of Selective Repeat

10. Efficiency Comparison

11. Sheet 9 problem 1  The message size is 10KB, transmission rate is 1Mbps. The frame has fixed size 1500B (including headers). The header size is 300B. The ACK size is also 300B. The processing time is 10 μ sec. in each machine. Assume electrical signals propagate at a speed of 2*10^8 m/sec. and the distance of the physical channel is 500m.  I. Plot the time diagram and sliding window(s) within first nine frames then find the total time required to deliver all frames assuming error free channel.  II. The Effective transmission rate (Reff).  III. Assuming error free channel, find the transmission efficiency ( η No Error)  IV. If the first frame received in error and Tout = 50msec, plot the time diagram and sliding window(s) within first three frames, then find the transmission efficiency.

12. Sheet 9 problem 1

16. Sheet 9 problem 2  A 64-kilobyte message is to be transmitted from the source to the destination. The network limits packets to a fixed size of two kilobytes, and each packet has a 32-byte header. The transmission lines in the network have a bit error rate of 10 6, and Stop-and- Wait ARQ is used in each transmission line.  How long does it take on average to get the message from the source to the destination? Assume that the signal propagates at a speed of 2x108 km/second.

17. Sheet 9 problem 2  Stop-and-Wait ARQ  File size = 64 kB  Pkt size = 2 kB (including 32 B header)  Bit Error Rate (BER) = 10^-6  Signal Speed = 2x10^8 km/second  Neglect Tproc. And Ta (Tt of ACK)

18. Sheet 9 problem 2