Algorithm for Dynamic Time out timer Calculation Last Updated : 09 Aug, 2019 Comments Improve Suggest changes Like Article Like Report Prerequisite – Computer Network | TCP Timers Calculating Time out timer (TOT) at transport layer is tricky as propagation delay is not constant i.e. path may change continuously and traffic is dynamic. So, static TOT cannot be used at TCP. And unnecessarily retransmitting the same data packet multiple times may cause congestion. Solution for this is we need dynamic TOT which can adjust to changes in round trip time (RTT). Algorithm for Dynamic TOT calculation: Basic algorithm Jacobson's algorithm Karn's modification 1. Basic algorithm - We assume initial round trip time i.e PRTT. On sending out each packet TOT = 2 * PRTT. The next round trip time is calculated using PRTTn+1 = α PRTTn + (1 - α)ARTTn where PRTT = predicted round trip time ARTT = actual round trip time α = smoothing factor such that 0<= α <=1 Example - Let PRTT1 = 10ms and α = 0.5 TOT = 2 * PRTT1 = 20ms Let ARTT1 = 15ms Then, PRTT2 = (0.5 * 10) + (0.5 * 15) = 12.5ms TOT = 2 * 12.5 = 25ms Let ARTT2 = 20ms PRTT3 = (0.5 * 12.5) + (0.5 * 20) = 16.25ms TOT = 2 * 16.25 = 32.5ms And so on TOT is calculated. Advantages - better than static TOT. TOT is flexible to dynamic round trip time. It takes into consideration all packets to derive new PRTT. Disadvantages - TOT = 2 * PRTT is used to allow a grace time for returning acknowledgement. It is wasteful. 2. Jacobson's algorithm - Calculates TOT value more intuitively than basic algorithm. We assume initial round trip time i.e. PRTT. PRTTn+1 = α PRTTn + (1 - α)ARTTn PDn+1 = α PDn + (1 - α)ADn where ADn = |PRTTn - ARTTn| AD = Actual deviation PD = predicted deviation On sending out each packet, TOT = (4 * PD) + PRTT. Example - Iteration 1 Given α = 0.5, PRTT1 = 10ms, PD1 = 5ms and ARTT1 = 20ms TOT = (4 * 5) + 10 = 30ms AD1 = |10 - 20| = 10ms Iteration 2 PRTT2 = α PRTT1 + (1 - α)ARTT1 = (0.5 * 10) + (0.5 * 20) = 15ms PD2 = α PD1 + (1 - α)AD1 = (0.5 * 5) + (0.5 * 10) = 7.5ms TOT = (4 * 7.5) + 15 = 45ms Given ARTT2 = 30ms AD2 = |15 - 30| = 15ms Iteration 3 PRTT3 = α PRTT2 + (1 - α)ARTT2 = (0.5 * 15) + (0.5 * 30) = 22.5ms PD3 = α PD2 + (1 - α)AD2 = (0.5 * 7.5) + (0.5 * 15) = 11.25ms TOT = (4 * 11.25) + 22.5 = 67.5ms Given ARTT3 = 10ms AD2 = |22.5 - 10| = 12.5ms And so on TOT is calculated. Problem with Basic and Jacobson's Algorithm In both, PRTTn+1 = α PRTTn + (1 - α)ARTTn i.e both depend on previous segment ARTT. But if initial time out timer times out then what next TOT will be chosen since the acknowledgement is delayed i.e its coming after time out so ARTT is not available. 3. Karn's Modification - Whenever the timer times out do not apply either of Basic or Jacobson algorithm as ARTT is not available instead double the time out timer(TOT) whenever the timer times out and a retransmission is made. GATE | Gate IT 2007 | Question 13 Comment More infoAdvertise with us Next Article Algorithm for Dynamic Time out timer Calculation A Ankit87 Follow Improve Article Tags : Misc Technical Scripter Computer Networks GATE CS Practice Tags : Misc Similar Reads Program to calculate the Round Trip Time (RTT) Round trip time(RTT) is the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgment of that signal to be received. This time, therefore, consists of the propagation times between the two-point of the signal. On the Internet, an end-user can determine th 2 min read How to Calculate Expected Round Trip Time? Round-trip time (RTT) is a critical metric in computer networks that measures the time it takes for a data packet to travel from a source to a destination and back again. It plays a crucial role in various networking protocols and is used to determine network performance, estimate latency, and optim 5 min read Step Count Method for Time Complexity Analysis What is Time Complexity? Time Complexity is the amount of time taken by the algorithm to run. It measures the time taken to execute each statement of code in an algorithm. Time Complexity can be calculated by using Two types of methods. They are: Step Count MethodAsymptotic Notation. Here, we will d 4 min read Program for HRRN CPU Scheduling Algorithm The Highest Response Ratio Next (HRRN) scheduling algorithm is a non-preemptive scheduling technique used in operating systems to manage the execution of processes. It is designed to improve upon simpler algorithms like First-Come-First-Serve (FCFS) and Shortest Job Next (SJN) by balancing both the 15 min read Longest Remaining Time First (LRTF) or Preemptive Longest Job First CPU Scheduling Algorithm Longest Remaining Time First (LRTF) is a preemptive version of Longest Job First (LJF) scheduling algorithm. In this scheduling algorithm, we find the process with the maximum remaining time and then process it, i.e. check for the maximum remaining time after some interval of time(say 1 unit each) t 7 min read How to set an input time limit in Python? In this article, we will explain how to set an input time limit in Python. It is one of the easiest programming languages which is not only dynamically typed but also garbage collected. Here we will look at different methods to set an input time limit. Below are the methods we will use in this artic 6 min read JavaScript - How To Create A Countdown Timer? A countdown timer is a timer that runs for a specific time limit and when that limit get crossed then it stops the timer and the message get displayed on the screen. it can be used for a website or blog to display the countdown to any special event, such as a birthday or anniversary.The Basics of a 4 min read Timer in C++ using system calls The task is to create timer without using any graphics or animation. The timer will be made using system calls wherever necessary. Timer in this context means a stopwatch with up-counting of time.The timer is created in Linux. Following system calls of Linux are used: sleep() : It will make the prog 2 min read Add given n time durations Given n time durations in the form of MM : SS, where MM denotes minutes and SS denotes seconds. The task is to add all the time duration and output answers in the form of HH : MM : SS. Examples: Input : n = 5 duration1 = 0 : 45 duration1 = 2 : 31 duration1 = 3 : 11 duration1 = 2 : 27 duration1 = 1 : 6 min read Java.util.Timer Class in Java Timer class provides a method call that is used by a thread to schedule a task, such as running a block of code after some regular instant of time. Each task may be scheduled to run once or for a repeated number of executions. Each timer object is associated with a background thread that is responsi 6 min read Like