Karn's Algorithm for Time out Timer

Duration: 3 min

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Module outline

  1. General Intelligence & Reasoning: Analogy, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Blood Relations, Directions (Direction Test), Ranking, Order and Sequence, Logical Sequence Of Words, Syllogisms, Venn Diagram, Deductive and Inductive Reasoning (Logical Deduction and Induction) (Prepositional Reasoning), Selection Decision Table (Decision Making), Data Sufficiency, Puzzle Solving (Puzzles), Data Arrangement, Cubes & Dices, Calendar, Clock, Arithmetic, Number System, HCF LCM, Verbal Analogy (Word Based Analogy), Visual Recognition and Figure Completion, Paper Folding and Cutting, Transformation of Shapes, Clocks and Calendars, Direction Sense, Cubes and Dice, Patterns in Two-Dimensional Figures, Seating Arrangements, Analogy and Classification, Logical Deduction and Induction, Alphabet and Word Tests, Mathematical Operations, Series Completion, Simplification and Approximation, Coding and Decoding, Numerical Reasoning, Assembling and Grouping of Shapes, Three-Dimensional Patterns and Visualization, Vocabulary, Number System, Averages, Mixtures and Alligation, Simple and Compound Interest, Percentages, Algebra, Speed, Time and Distance, Seating and Arrangement Puzzles, Traverse Surveying, Order, Ranking and Sequence, Constraint Puzzles, Syllogisms and Venn Diagrams, Reading Comprehension, Critical Reasoning, Permutations and Combinations, Narrative Sequencing, Project Monitoring, Resources and Safety, Profit, Loss and Discount, Ratio and Proportion, Time and Work, Mensuration, Data Interpretation, Powers, Surds and Logarithms, Sequences and Series, Articles and Determiners, Sentence Completion, Data Sufficiency, Blood Relations, Simple Interest and Compound Interest, Mixture and Alligation, Sequence and Series (Series), Speed Time and Distance, Algebra, Profit and Loss, Powers and Exponents (Surds and Indices), Permutation and Combination
  2. General Awareness: Physics, Chemistry, Biology, History, Geography, Polity, Indian Economy, Environment, Static General Knowledge, GK- Current Affairs, Artificial Intelligence, MS Office Applications, Terms & Abbreviations, Keyboard Shortcuts, Evolution of Indian Banking (Banking & Financial Awareness), Emerging Tech Trends
  3. Engineering Mathematics: Set Theory, Relations, Functions, Graph Theory, Group Theory, Propositional and Predicate Logic, Linear Algebra, Calculus, Probability, Statistics, Signal Space and Optimum Detection, Probability, Statistics
  4. Digital Logic: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Number System, Number Representation, Floating Point Rep, Number Systems and Codes, Registers and Counters, Boolean Algebra and Logic Gates, Microprocessors and Microcontrollers, Logic Families and CMOS Logic, Microprocessors, Logic Gates and Boolean Algebra, Minimization of Boolean Functions, Timing, Hazards and Testing, Logic Families, Combinational Logic Design, Arithmetic Circuits, Waveform Generators and Timer Circuits, Semiconductor Memories and Programmable Logic Devices, Combinational Logic Circuits, Latches and Flip-Flops, Finite State Machines, Sequential Circuits and State Machines, Minimization of Boolean Functions, Arithmetic Circuits, Latches and Flip-Flops, Number Systems and Codes, Registers and Counters
  5. Computer Organisation & Architecture: Basics of COA, Cache Memory Organization, Input Output Organisation, Pipelining, Instr Formats & Modes, Control Unit Design, Programming the Basic Computer, Register Transfer and Microoperations, Semiconductor Memories and Programmable Logic, Processor Organization and Instructions, Memory Hierarchy and Input/Output, Registers and Counters
  6. Programming & Data Structures: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling, Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing, HTML Basics, OOPS with C++, Java, Object Oriented Technology
  7. Databases: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, File Organization & Indexing, Relational Algebra, SQL, Relational Calculus, Transaction Management, Concurrency Control, Database Recovery, Database Security & Authorization
  8. Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos
  9. Theory of Computation: Introduction to TOC, Deterministic FA (DFA), Non-Deterministic FA, Regular Expressions, Grammar, Regular Language Properties, Moore & Mealy Machines, Pushdown Automata & CFG, Turing Machines, Complexity Theory
  10. Compiler Design: Intro to Compilers, Lexical Analysis, Grammar & CFG, Syntax Analysis: Top-Down, Syntax Analysis: Bottom-Up, Semantic Analysis & SDT, Intermediate Code Gen, Code Optimization, Run Time Environment
  11. Operating System: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Threads & Process Creation, Deadlock, Memory Management, Virtual Memory, Disc Scheduling, File Management, Security, Windows OS, Distributed Systems, Unix OS, Linux OS
  12. Computer Networks: Introduction to CN, DLL: Access Control, DLL: Flow Control, DLL: Error Control, DLL: Framing, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Net Layer:Routing Protocol, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware Basics, Data Communication, Website, Browser & Services, Web Design & Development, Network Security, Cyber Threats and Malware Attacks, Cyber Safety and Security
  13. Full Length Mock Tests:
  14. Sectional Tests:
  15. Paper 2 - Full-length Mock Tests:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This lecture segment introduces Karn's Algorithm for TCP timeout timers, focusing on the limitations of basic and Jacobson's algorithms. The instructor explains that both prior methods rely on the actual round-trip time (ARTT) of previous segments to calculate the initial round-trip time (IRTT), using the formula IRTT_{n+1} = α IRTT_n + (1 − α) ARTT_n. A critical problem arises when a segment is retransmitted after its timeout expires: the acknowledgment (ACK) arrives too late to provide a valid ARTT measurement, making standard updates unreliable. The instructor demonstrates this with a numerical example, showing how IRTT values shift from initial estimates (e.g., 10 and 15) to updated figures (12.5 and 25) when invalid data is incorporated. Karn's modification, proposed by Phil Karn and Craig Partridge in 1987, resolves this issue. The core rule is that when a segment is retransmitted due to timeout, the sender must not use the resulting ACK's RTT for estimation; instead, it should double the timeout timer (TOT) to account for potential congestion. This approach prevents skewed IRTT calculations and improves TCP reliability.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The slide titled 'Problems with Basic Algorithm and Jacobson's Algorithm' presents the core issue: both algorithms depend on previous ARTT via IRTT_{n+1} = α IRTT_n + (1 − α) ARTT_n. The instructor uses red pen to underline 'Basic Algorithm' and cross out the α IRTT_n term, emphasizing the dependency problem. A numerical example follows where initial IRTT values of 10 and 15 are crossed out and replaced with 12.5 and 25, illustrating how invalid ACKs after timeout corrupt the estimate. The slide notes that 'Consider ACK of some segment arrives to the sender after its initial time out timer goes off,' highlighting why standard updates fail in retransmission scenarios.

  2. 2:00 – 2:57 02:00-02:57

    The lecture transitions to Karn's solution with a slide stating that Karn's algorithm estimates round-trip time for TCP messages, proposed by Phil Karn and Craig Partridge in 1987. Red annotations underline 'Karn' and 'Craig Partridge,' with an arrow pointing to a portrait. The next slide, 'Karn's Modification,' lists the key rule: when a segment is retransmitted (underlined in red), do not use its ACK for RTT estimation. Instead, double the timeout timer (TOT), as emphasized by a red underline and curved stroke beneath 'time out timer (TOT).' Red X marks over 'Basic' and 'Jacobson's' reinforce that this modification supersedes earlier approaches.

The lesson progresses from problem identification to solution. First, it establishes that basic and Jacobson's algorithms fail when ACKs arrive after timeout because they incorporate invalid ARTT data into IRTT calculations. The numerical example concretizes this flaw by showing how estimates drift when corrupted data is used. Karn's modification then provides a clear corrective rule: ignore RTT measurements from retransmitted segments and double the timeout timer instead. This two-part strategy—excluding invalid data and adjusting for congestion—ensures more accurate IRTT estimation. The instructor's red pen annotations (cross-outs, underlines, arrows) visually reinforce these key points, distinguishing the problematic terms in the formula and highlighting Karn's specific modifications. The content is grounded entirely in visible slide text and annotations, with no audio transcript available to confirm additional verbal explanations.

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