Selective Repeat - ARQ

Duration: 5 min

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Inside: a video lesson and guided study material.

Module outline

  1. About Course: About the Course
  2. Paper 1 | General Studies: State Wise GK
  3. Paper 1 | Information and Communication Technology: Role of Internet and Web Services, Security in Mobile and Wireless Computing
  4. Paper 1 | Current Affairs: GK- Current Affairs
  5. Paper 2 | Discrete Mathematical Structure: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Set Theory, Relations, Functions, Graph Theory, Group Theory, Propositional and Predicate Logic, Probability
  6. Paper 2 | Digital Computer Organization And Architecture: Number System, Number Representation, Sequential Circuits, Combinational Circuit, Basics of COA, Floating Point Rep, Cache Memory Organization, Input Output Organisation, Pipelining, Instr Formats & Modes, Register Transfer and Microoperations, Control Unit Design, Programming the Basic Computer
  7. Paper 2 | C Programming: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling
  8. Paper 2 | Programming Languages & Object-Oriented Programming Concepts: Java, OOPS with C++, Java Fundamentals, Array, String, IO & References
  9. 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
  10. Paper 2 | Data Structure And Algorithms: Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing, Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Minimum Spanning Trees, Advanced Algorithms
  11. Paper 2 | Operating System: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Deadlock, Threads & Process Creation, Memory Management, Virtual Memory, Disc Scheduling, File Management, Unix OS
  12. Paper 2 | 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
  13. Paper 2 | 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
  14. 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, Transaction Management, Concurrency Control, Database Recovery, Database Security & Authorization, Enhanced Data Models
  15. Paper 2 | Computer Network And Information Security: Introduction to CN, Data Communication, Application Layer, Hardware basics, Cyber Threats and Malware Attacks, Network Security, 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
  16. Paper 2 | Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management
  17. Paper 2 | Current Trends & Technologies: Emerging Tech Trends, Approaches to AI, Search Algorithms, Game Playing, Knowledge Representation, Planning, Multi Agent Systems, Fuzzy Sets, Natural Language Processing, Artificial Neural Networks, Genetic Algorithms, Artificial Intelligence, Data Warehousing & Mining, Electronic Data Interchange and E-Commerce, Terms & Abbreviations
  18. Paper 2 | Full Length Mock Tests:
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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