TCP Header-Header Length Field

Duration: 3 min

This video lesson is available to enrolled students.

Return to /learn/HPSC-PGT-COMPUTER-SCIENCE/computer-networks/transport-layer-services/tcp-header-fields/asset-tcp-header-header-length-field after enrolling

Inside: a video lesson and guided study material.

Module outline

  1. HPSC Interview Preparation: Interview Preparation
  2. Python Language: Introduction to Python, Tokens, Variables, Data Types, I/O, Operators & Expressions, Control Flow & Looping, Collections & Strings, Functions & Modules, File Handling & Data Analysis, DSA using Python
  3. Data Structure & Algorithms: Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing, Algorithm Analysis, Sorting Algorithms, Minimum Spanning Trees, Time Complexity Analysis, Graph Theory, Shortest Path Algos
  4. Computer Networks: Introduction to CN, Data Communication, DLL: Access Control, DLL: Flow Control, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware basics, Network Security
  5. Computer System & Organisation: Basics of COA, Cache Memory Organization, Input Output Organisation, Pipelining, Instr Formats & Modes, Control Unit Design, Programming the Basic Computer
  6. Database Management System: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, SQL, File Organization & Indexing, Transaction Management, Concurrency Control
  7. Operating Systems: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Deadlock, Threads & Process Creation, Memory Management, Virtual Memory, Disc Scheduling
  8. Digital Logic & Circuits: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Number System, Number Representation
  9. Theory Of Computation: Introduction to TOC, Deterministic FA (DFA), Non-Deterministic FA, Regular Expressions, Grammar, Regular Language Properties, Pushdown Automata & CFG, Turing Machines, Moore & Mealy Machines
  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. Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management, Data Warehousing & Mining
  12. Introduction to Emerging Trends: Emerging Tech Trends
  13. Digital Society & Cyber Law: Society, Law & Ethics
  14. HPSC PGT Previous Year Paper:
  15. HPSC Assistant Professor Previous Year Paper:
  16. Live Sessions: HPSC Live Sessions, EMRS TGT/PGT Live Class
  17. Full Mock Test:
  18. HPSC PGT - MOCK Test Series:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This lecture segment explains the TCP header length field, emphasizing that it is a 4-bit value representing the number of 4-byte words in the header. The instructor shows that the field can range from 5 to 15, producing a total header length of 20 to 60 bytes. The formula “Header length = Header length field value x 4 bytes” is used repeatedly to connect the bit-field value with actual byte count. The slide also identifies the adjacent 6-bit Reserved field as space kept for future use, and includes a TCP segment diagram with header and data blocks plus a table of header fields such as source/destination port, sequence number, acknowledgment number, HLEN, Reserved, window size, checksum, urgent pointer, and options/padding.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The instructor introduces the TCP header length field using a slide that states it is a 4-bit field indicating the number of 4-byte words in the TCP header. The on-screen formula “Header length = Header length field value x 4 bytes” is highlighted, and the instructor explains that valid values are from 5 to 15, giving a header length of 20 to 60 bytes. The slide also shows the adjacent “Reserved” field as a 6-bit space reserved for future use. Around the middle of this window, the instructor writes bit examples on the board, including “0000” and “1111 (15),” to illustrate how the 4-bit field maps to decimal values and byte lengths.

  2. 2:00 – 3:00 02:00-03:00

    The slide remains focused on the “Header length” topic, showing that the 4-bit field corresponds to 20 to 60 bytes and that values run from 5 (5 x 4 = 20) to 15 (15 x 4 = 60). A bullet under “Concept of Scaling Factor” repeats the formula “Header length = Header length field value x 4 bytes,” while another line notes that Reserved is a 6-bit field reserved for future use. A segment diagram labeled “a. Segment” shows Header and Data blocks, with a TCP header table listing Source/Destination port address, Sequence number, Acknowledgment number, HLEN 4 bits, Reserved 6 bit, Window size, Checksum, Urgent pointer, and Options and padding (up to 40 bytes). A hand points at the HLEN cell, and handwritten “1111 (15) = 60” appears in the margin.

The central teaching point is that TCP header length is not stored directly in bytes but as a 4-bit count of 32-bit words. Because each word is 4 bytes, the actual header length equals the field value multiplied by 4. The minimum useful value is 5, giving a basic header of 20 bytes; the maximum possible 4-bit value is 15, giving 60 bytes. The lecture reinforces this with the formula “Header length = Header length field value x 4 bytes” and connects it to the TCP segment structure, where options and padding can extend the header up to 40 extra bytes. The Reserved field is presented as a minor adjacent detail: a 6-bit area kept for future use. The progression moves from defining the field, to showing its numeric range, to applying the scaling formula, and finally locating HLEN within the full TCP header table.

Loading lesson…