Selective Repeat - ARQ

Duration: 5 min

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Module outline

  1. About the Course: About the Course
  2. Paper-1 & 2 | Basic Numeracy: Ratio and Proportion (Ratios), Divisibility Rules, Mixture and Alligation, Permutation and Combination, Logarithm, Number System, HCF LCM, Sequence and Series (Series), Speed Time and Distance, Percentage, Average, Mensuration and Geometry, Age Problems, Arithmetic, Statistics, Probability, Profit and Loss, Simple Interest and Compound Interest, Partnership, Speed Mathematics and Basic Mathematics, Algebra, Powers and Exponents (Surds and Indices), Time and Work, Pipe and Cistern, RSSB Specific Videos - Basic Numeracy
  3. Paper-1 & 2 | Data Interpretation: Data Interpretation
  4. Paper-1 & 2 | General Mental Ability: Mental Ability, RSSB Specific Videos - Mental Ability
  5. Paper-1 & 2 | Logical Reasoning and Analytical Ability: Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Data Sufficiency, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Syllogisms, Seating Arrangements, Blood Relations, Directions (Direction Test), Analytical Reasoning (Counting Figures Reasoning), Puzzle Solving (Puzzles), Calendar, Clock, Cubes & Dices, Venn Diagram, Analogy, Ranking, Order and Sequence, Deductive and Inductive Reasoning (Logical Deduction and Induction) (Prepositional Reasoning), Data Arrangement, Logical Sequence Of Words, Crypt Arithmetic
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  7. Paper-1 | General Science: Physics, Biology, Chemistry, RSSB Specific Videos
  8. Paper-1 | General Awareness: State Wise GK, GK- Current Affairs
  9. Paper-2 | Fundamentals of Computer: Basics of COA, Number System, Floating Point Rep, Number Representation
  10. Paper - 2 | Digital Logic Systems: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits
  11. Paper-2 | Operating Systems: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Deadlock, Threads & Process Creation, Memory Management, Virtual Memory, Disc Scheduling, File Management, Linux OS, Distributed Systems
  12. Paper-2 | Database Management System: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, Relational Algebra, SQL, Relational Calculus, File Organization & Indexing, Transaction Management, Concurrency Control
  13. Paper-2 | Data Structures: Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing
  14. Paper-2 | C Programming: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling
  15. Paper 2 | Oops, C++, Java: Language Design, OOPS with C++, Java, .Net Programming, Java Fundamentals
  16. Paper 2 | Python: Introduction to Python, Tokens, Variables, Data Types, I/O, Operators & Expressions, Control Flow & Looping, Collections & Strings, Functions & Modules, File Handling & Data Analysis
  17. Paper 2 | Emerging Trends and AI: Emerging Tech Trends, Artificial Intelligence
  18. Paper-2 | Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Advanced Algorithms
  19. Paper 2 | Data Communication and Network Security: Introduction to CN, Data Communication, DLL: Access Control, DLL: Flow Control, DLL: Error Control, 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, Network Security, Ethical Hacking
  20. Paper-2 I Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management
  21. Paper-2 | Computer Organization and Architecture: Cache Memory Organization, Input Output Organisation, Instr Formats & Modes, Control Unit Design, Register Transfer and Microoperations
  22. Paper-2 | Web Development: JavaScript-Basics, HTML Basics, CSS, XML
  23. Pedagogy: Child Development, Concept of Pedagogy, Psychology, Theories, Inclusive Education, Experiential Pedagogy, Curriculum Framework & Reforms, National Education Policy (NEP) 2020
  24. Live Sessions: RSSB Live Sessions
  25. RSSB Paper 1 - Full Mock Tests:
  26. RSSB Paper 2 - Full Mock Tests:
  27. SCI Previous Year Papers:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This lecture introduces Selective Repeat Automatic Repeat Request (ARQ), a protocol designed for noisy links where only damaged frames are resent rather than multiple frames. The instructor contrasts this with Go-Back-N ARQ, emphasizing that Selective Repeat requires the sender and receiver window size to be at most one-half of 2^m. The session progresses through timer handling mechanisms, where a tree diagram illustrates that one timer is used for each frame sent. Key events include the loss of Frame 1, triggering a NAK and subsequent retransmission of specific frames. The instructor explains that if a valid NAK frame arrives, the sender resends only the corresponding frame. The lecture concludes with mathematical derivations for sequence and acknowledgement numbers, utilizing formulas like $W_s = (1 + 2a)$ to maximize efficiency and calculating bits required as $ ext{ceil}( ext{log}_2(1 + 2a))$.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The video begins with a presentation slide titled "Selective Repeat Automatic Repeat Request" contrasting the protocol with Go-Back-N ARQ. Text on screen explains that for noisy links, a mechanism exists where only damaged frames are resent rather than multiple frames. The scene shifts to a detailed timing diagram illustrating communication between Sender A and Receiver B, showing frame transmission, acknowledgments, a lost frame event, and subsequent retransmission. Visible text notes that the sender and receiver window size must be at most one-half of 2^m.

  2. 2:00 – 5:00 02:00-05:00

    The instructor explains the timer handling mechanism in Selective Repeat ARQ, drawing a tree diagram to illustrate how timers are managed for each frame sent. The slide details a sequence where Frame 1 is lost, triggering a NAK and subsequent retransmission of frames. The instructor highlights the NAK arrow to emphasize that a valid NAK triggers a retransmission of only the specific missing frame. On-screen text states, "If a valid NAK frame arrives, we just resend the corresponding frame," and shows Frame 1 (resend) following a NAK.

  3. 5:00 – 5:26 05:00-05:26

    The video features a lecturer explaining "Sequence and Acknowledgement Numbers" for Selective Repeat ARQ. The whiteboard displays formulas for maximizing efficiency, specifically the window size $W_s = (1 + 2a)$ and the bits required $ ext{ceil}( ext{log}_2(1 + 2a))$. Handwritten calculations show the derivation of sequence number bits, starting with $75 + 1 = 76$ and comparing powers of 2 like $2^6=64$, $2^7=128$, and $2^8=256$. The instructor writes out utilization formulas involving transmission time ($T_T$) and propagation delay ($T_P$).

The lecture systematically builds understanding of Selective Repeat ARQ by first defining its core advantage over Go-Back-N: selective retransmission of only damaged frames. The instructor uses visual timing diagrams to demonstrate the protocol's operation, specifically focusing on how lost frames trigger NAKs and specific retransmissions. A critical constraint highlighted is the window size limitation of $2^{m-1}$ to prevent ambiguity. The session concludes with practical mathematical applications, deriving the necessary sequence number bits and window sizes to maximize channel utilization based on propagation delay and transmission time. This progression from conceptual definition to operational mechanics and finally to mathematical optimization provides a comprehensive overview of the protocol's design principles.

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