Computer Networks
CN Part-1
- What is a Computer Network?
- Goals and Applications of Computer Networking
- Computer Network Components
- Types of Computer Networks
- Network Topology
- Difference between Client Server and Peer to Peer Network
- Layered Architecture in Computer Networks
- Protocol Hierarchy in Computer Networks
- Interfaces and Services in Computer Networks
- Connection Oriented and Connectionless Services
- Service Primitives
- OSI Model
- TCP/IP Model
- Difference between OSI Model and TCP/IP Model
- Encapsulation and Decapsulation in Computer Networks
- Queueing Models in Computer Network
CN Part-2
- Physical Layer in Computer Networks
- Transmission Media in Computer Networks
- Analog and Digital Signals
- Data Rate and Bandwidth
- Encoding Techniques
- Multiplexing in Computer Networks
- Transmission Modes in Computer Networks
- Data Link Layer
- Framing in Data Link Layer
- Flow Control in Data Link Layer
- Error Control in Data Link Layer
- Error Detection and Correction in Computer Networks
- Stop and Wait Protocol
- Sliding Window Protocol
- SDLC(Synchronous Data Link Control) Protocol
- High-Level Data Link Control (HDLC) Protocol
- Point-to-Point Protocol (PPP)
CN Part-3
- MAC Sublayer and MAC Addressing
- Channel Allocation Methods
- ALOHA Protocol (Pure and Slotted ALOHA)
- CSMA/CD and CSMA/CA in Computer Networks
- Ethernet (IEEE 802.3)
- Wireless LANs (IEEE 802.11, Wi-Fi, and Bluetooth Basics)
- Network Layer and Design Issues
- IPv4 and IPv6 Protocols
- Addressing: IP Address, Subnetting, and Supernetting
- Routing Algorithms: Static vs Dynamic, Distance Vector, and Link State
- Routing Protocols: RIP, OSPF, and BGP
- Packet Switching and IP Fragmentation
- Network Layer Protocols: ICMP, ARP, RARP, DHCP, and NAT
CN Part-4
- Transport Layer and Functions
- Process-to-Process Delivery, Ports, and Sockets
- TCP Segment and Three-Way Handshake Connection Establishment
- UDP (User Datagram Protocol): Format and Features
- Flow Control and Error Control in Transport Layer
- Congestion Control: Leaky Bucket, Token Bucket, and TCP Congestion Control
CN Part-5
- Application Layer Architecture and Principles
- Domain Name System (DNS)
- Email Protocols: SMTP, POP3, and IMAP
- File and Web Protocols: FTP, HTTP, and HTTPS
- Remote Access Protocols: Telnet and SSH
- World Wide Web (WWW) and Web Architecture
- Network Security Basics: SSL, TLS, and Cryptography Fundamentals
Transport Layer and Functions in Computer Networks
Transport Layer kya hai? (What is Transport Layer?)
Transport Layer OSI Model ki Layer 4 hoti hai, jise networking ka “Heart of OSI Model” kaha jaata hai.
Yeh Upper application software layers (Application, Presentation, Session) aur Lower hardware network layers (Network, Data Link, Physical) ke beech ek vital bridge ka kaam karti hai.
Network layer packets ko sirf ek computer se doosre computer (Host-to-Host) tak pahunchati hai. Lekin aapke computer par ek saath Chrome, WhatsApp, Zoom aur Spotify chal rahe hain. Network layer se aane wala packet computer ke kis particular software application ke liye hai? Yeh ensure karna Transport Layer ka kaam hai (jise Process-to-Process Delivery kehte hain).
Transport Layer par data unit ko Segment (TCP ke liye) ya User Datagram (UDP ke liye) kaha jaata hai.
Core Functions of Transport Layer
-> Service-Point (Port) Addressing: Har running application process ko ek unique 16-bit Port Number assign karta hai taaki data sahi application tab tak deliver ho.
-> Segmentation and Reassembly: Application layer se aane wale bade message ko manageable pieces (Segments) mein divide karta hai, har segment ko Sequence Number deta hai, aur receiver par unhe sequentially reassemble karta hai.
-> Connection Control: Do tarah ki services provide karta hai: Connection-Oriented (TCP) with 3-way handshake, aur Connectionless (UDP).
-> Flow Control: End-to-End flow control provide karta hai using Sliding Window protocol taaki fast sender slow receiver ke buffer ko overflow na kare.
-> Error Control: Checksum aur ARQ mechanisms ke zariye corrupted, lost, ya duplicate segments ko detect karke retransmission ensure karta hai.
-> Multiplexing and Demultiplexing: Multiple applications ke data streams ko combine karke single network layer ko dena (Multiplexing) aur destination par alag-alag apps ko deliver karna (Demultiplexing).
Data Link Layer Flow/Error Control vs Transport Layer Flow/Error Control
College exams mein aksar students confuse hote hain ki Layer 2 aur Layer 4 dono flow/error control karti hain, toh farq kya hai?
| Parameter | Data Link Layer (Layer 2) | Transport Layer (Layer 4) |
|---|---|---|
| Scope of Delivery | Node-to-Node (Hop-to-Hop): Sirf do directly connected padosi switches ya routers ke beech. | End-to-End (Process-to-Process): Source application se final destination application tak. |
| Addressing Used | Physical MAC Address (48 bits). | Port Address / Socket Address (16 bits). |
| Intermediate Routers | Har intermediate router Layer 2 frame ko unpack aur check karta hai. | Intermediate routers Transport layer header ko touch nahi karte; yeh sirf Source aur Destination end-hosts par run hota hai. |
Two Main Transport Layer Protocols
| Feature | TCP (Transmission Control Protocol) | UDP (User Datagram Protocol) |
|---|---|---|
| Connection Type | Connection-oriented (3-way handshake required). | Connectionless (No handshake, sends immediately). |
| Reliability | 100% Reliable (Acknowledgments, Retransmissions). | Unreliable (Best effort, no ACK, no retransmission). |
| Speed & Overhead | Slower (20 to 60 Bytes header, overhead of ACK). | Blazing Fast (Fixed 8 Bytes header, minimal overhead). |
| Use Cases | Web browsing (HTTP/HTTPS), File transfer (FTP), Emails (SMTP). | Live streaming, Online gaming, Video calls (Zoom), DNS queries. |
Summary Table
| Aspect | Summary Point |
|---|---|
| OSI Position | Layer 4 – True End-to-End layer connecting userspace software with the network. |
| Key Responsibility | Process-to-Process communication using 16-bit Port Numbers. |
| Protocols | TCP (Reliable, heavy) and UDP (Lightweight, real-time speed). |