Analyzing the effect of timer timeout and packet length on the performance of error control protocols

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1 Analyzing the effect of timer timeout and packet length on the performance of error control protocols Abstract: In the present day computer networks quality of service is a major issue, which invariably depends on the network performance under various network constraints such as flow control, error control, bandwidth, data traffic, buffer handling etc. In this paper we are Analyzing the Effect of Timer timeout and length on the performance of error control protocols and conclusions are drawn Keywords: Quality of Service, Go-Back-N ARQ, Selective Repeat ARQ, Timer Timeout, Length, Throughput 1. INTRODUCTION In computer networks, mostly we come across three types of errors. Lost frames Lost Acknowledgements Delayed Acknowledgements Most Error Control techniques are based on either Error Detection Scheme (e.g., Parity checks, CRC), or Retransmission Scheme. Error control schemes that involve error detection and retransmission of lost or corrupted frames are referred to as Automatic Repeat Request (ARQ) error control. Error control protocols, as the name implies, these protocols are used to recover from errors. When some user submits a message to the network to be transmitted to another user, the message is usually split into packets which are transmitted over the network and reassembled at the other end. A packet in transit encounters one or more channels, (e.g., satellite, copper wire or optical fiber), and nodes (or routers), which route the packet to the destination. These intermediate elements can induce errors in the packet in that either the packet could get garbled, or dropped altogether. The former is usually due to random electrical noise in the channels while the latter is due to buffer overruns at the nodes and is caused by contention for resources, a phenomenon often referred to as congestion. Two error control protocols that we are primarily interested in analysis are the Go-Back-N and the Selective Repeat protocols. We shall however not Shashi Kumar D1, Nagamani A2 1 Christ University, Faculty of Engineering, Kaniminike, Bangalore-56, India 2 Dept. of Electronics and Communication Engineering, Bhaskar Engineering College, Hyderabad, India consider the Stop-And-Wait protocol because it is known to perform poorly [1]. In both cases, an error is detected at the sender by either a timer interrupt or a NACK from the receiver. At this point, if the sender backs up to the first packet in error, i.e., the first packet that is not yet ACKed, and restarts the transmission, the strategy is referred to as Go-Back-N [2]. Figure 1: Go-Back-N ARQ with lost frame [2] If, on the other hand, the sender retransmits only those packets which are in error, the strategy is called selectiverepeat. Fig. 1, Fig. 2.and Fig. 3 shows the flow diagrams of Go-Back-N and Selective Repeat ARQ s. Figure 2 Go-Back-N ARQ with lost Acknowledgement [2] Volume 1, Issue 2 July-August 212 Page 19

2 (Timer Timeout vs. Throughput) Tout (ms) Figure 3: Selective Repeat ARQ with lost frame [2] 2. SIMULATIONS AND RESULTS The analysis on the performance of error control protocols, such as Go-Back-N ARQ and Selective Repeat ARQ is done by conducting experiments using BENCHMARK LAN TRAINER KIT and the simulation software. 2.1 Setting the configuration menu In both, the sender and receiver machines the following values needed to be entered in the configuration windows. After calculating the timer timeout values for various data rates experiments are conducted for constant experimental duration. Then the values of successful transmission are noted for different timer timeout values and packet lengths. TABLE 1: Configuration windows at sender and receiver PC 1 PC 2 Node Id Node Id Protocol CSMA/C D Protocol CSMA/C D Baud rate 8Kbps (at both the config menu and NEU) Baud Rate 8Kbps (at both the config menu and NEU) Duration 1s Duration 1s length 1 bytes Length 1 bytes Inter Delay 4 ms Inter Delay 4 ms Direction Sender Direction Receiver A. Go-Back-N ARQ TABLE 2: Results for Go-Back-N ARQ Figure 4: Timer Timeout Vs. Throughput TABLE 3: Results for Go-Back-N ARQ ( length Vs. Throughput) Pl in Bytes Volume 1, Issue 2 July-August 212 Page 191

3 Figure 5: length Vs. Throughput B. Selective Repeat ARQ TABLE 4: Results for Selective Repeat ARQ (Timer Timeout Vs. Throughput) Tout (ms) Figure 6: Timer Timeout Vs. Throughput TABLE 5: Results for Selective Repeat ARQ ( length Vs. Throughput) Pl in Bytes Figure 7: length Vs. Throughput C. Comparison of Go-Back-N ARQ & Selective Repeat ARQ Volume 1, Issue 2 July-August 212 Page 192

4 with Go-Back-N protocol for a given packet length. In the other hand Go-Back-N ARQ will give better throughput for lower values of length than compared to the Selective Repeat ARQ. 4. FORMULA USED Formula used to calculate throughput is. Figure 8: Timer Timeout Vs. Throughput Where = Throughput =Successfully Transmitted packets Pl= Length in Bytes De=Duration of Experiment in seconds Dr=Data rate in Kbps Tout= Timer Timeout value in seconds Figure 9: length Vs. Throughput 3. RESULT ANALYSIS The simulation results are obtained for Go-Back-N ARQ and Selective Repeat ARQ by varying packet length and Timer timeout values, using BENCHMARK LAN TRAINER KIT and the simulation software. Fig. 4 and Fig. 6 show the plots of Timer timeout Vs. Throughput for Go-Back-N ARQ and Selective Repeat ARQ. In this experiment, the value of packet length, 1Bytes and duration of the experiment, 3 seconds is taken for the simulation. From plots it is clear that as we increase the timer timeout, the throughput of the system is increasing up to certain level and then it is almost same for all other values. For the current scenario, the throughput is increasing up to the timeout value of 225; thereafter it is almost equal for all other values. Fig. 5 and Fig. 7 show the plots of length Vs. Throughput for Go-Back-N ARQ and Selective Repeat ARQ. From plots it is very clear that the throughput of the system will increase up to certain range of packet lengths then it returns back to zero and continuous to be in zero for further increase in the packet length. Fig. 8 and Fig.9 gives us the comparison results of Go- Back-N ARQ and Selective Repeat ARQ protocols for Timer timeout Vs. Throughput and length Vs. Throughput respectively. From these plots we can infer that for lesser timer timeout values we will get more throughput in case of Selective Repeat when compared 5. CONCLUSION AND FUTURE WORK In this paper we made an analysis of the effect of timer timeout values and packet length on throughput of data link layer error control protocols, conducting experiments using BENCH MARK LAN TRAINER KIT and simulation software without considering the bit errors. Further enhancement can be made to analyze the effect of timer timeout and packet length on the throughput of the system considering bit errors. Also we can analyze the effect of data rate on throughput. References [1] Zwaenepoel, W., Protocols for Large Data Transfers on Local Networks, Proc. of the ACM Sigcomm, pp 22-32, 1985 [2] Tanenbaum, A.S., Computer Networks, Prentice- Hall Inc.,Englewood Cliffs, NJ 7632, 1981 [3] S. Lin, D. J. Costello, Jr., and M. J. Miller, Automatic-repeat-requesterror-control scheme, IEEE Commun., vol. 22, pp. 5-17, Dec [4] M. Moeneclaey, H. Bruneel, I. Bruyland, and D. Y. Chung, Throughput optimization for a generalized stop-and-wait ARQ scheme, IEEE Trans.Commun., vol. COM-34, pp , Feb [5] Anagnostou, M.E. and E.N. Protonotarios, "Performance analysis of the selective repeat ARQ protocol," IEEE Trans.Commun., vol. COM-34, pp , Feb AUTHOR Shashi Kumar D received the B.E degree from SJC Institute of Technology in 27 and MTech degree in Electrical Engineering from Indian Institute of Technology Madras in 21. During June, 21- July, 211, he stayed in ICFAI University Dehradun as a Volume 1, Issue 2 July-August 212 Page 193

5 Faculty member, from July-211 to till date working as Assistant Professor in Christ University, Faculty of Engineering. Nagamani A received the B.Tech from Bhojreddy College of Engineering & Technology for women in 24, MTech degree in Electrical Engineering from Indian Institute of Technology Madras in 21, From August 21 to till date working as Assistant Professor in Bhaskar Engineering College (JB group of institutions). Volume 1, Issue 2 July-August 212 Page 194