TCP Retransmission

Duration: 4 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
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  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
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  8. Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos
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  13. Full Length Mock Tests:
  14. Sectional Tests:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This lecture explains TCP retransmission, focusing on how a sender recovers from lost segments. The instructor first introduces the two mechanisms that trigger retransmission: timeout timer expiry and receipt of three duplicate acknowledgements. The first part details the timeout process, where a sender starts a timer for each segment; if an ACK is not received before the timer expires, the same segment is retransmitted. The second part introduces fast retransmission using a worked example of five segments where segment 2 is lost. The receiver sends an original ACK for segment 1, then duplicate ACKs upon receiving segments 3, 4, and 5. After the sender receives three duplicate ACKs requesting segment 2, it retransmits segment 2 immediately without waiting for the timer to expire. This is termed early or fast retransmission.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The lecture begins with a slide titled 'TCP Retransmission,' explaining that a lost segment causes the receiver to send an acknowledgement with the same ACK number. The instructor outlines two triggers for retransmission: 'Either Time Out Timer expire or it receives three duplicate acknowledgements.' The slide then transitions to 'Retransmission after Time out Timer Expiry,' showing a Sender-Receiver diagram. A red X marks the 'Lost Segment' before it reaches the receiver, while a timer icon tracks from 'Timer Starts' to 'Timer Expires.' A blue arrow labeled 'Retransmit Same Segment' illustrates the sender's action after expiry.

  2. 2:00 – 4:13 02:00-04:13

    The instructor presents a worked example where 'Sender sends 5 TCP segments' and the second segment is lost. The receiver's behavior is detailed: it sends an original ACK for segment 1, followed by the '1st duplicate ACK' upon receiving segment 3. As segments 4 and 5 arrive, the receiver sends the '2nd' and '3rd duplicate ACKs,' all asking for segment 2. The diagram shows a red X over 'Segment 2' and labels reading '3 duplicate acks received.' The instructor concludes that the sender retransmits segment 2 without waiting for its timer to go off, a process identified as 'early retransmission or Fast retransmission.'

The lesson progresses from general TCP recovery principles to a specific fast retransmission scenario. The core concept is that TCP uses two distinct methods to handle packet loss: a passive timeout mechanism and an active fast retransmission triggered by duplicate ACKs. The worked example of five segments effectively demonstrates how the receiver's inability to process out-of-order data (segments 3-5) generates duplicate ACKs. This allows the sender to infer loss and act faster than a timeout would permit, which is central to maintaining efficient data flow.

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