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
SDLC (Synchronous Data Link Control) Protocol
SDLC kya hai?
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SDLC ek bit-oriented protocol hai jo IBM ne develop kiya tha.
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Yeh OSI Model ke Data Link Layer (Layer 2) par kaam karta hai.
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Iska kaam hai data ko synchronous link par reliable tareeke se bhejna aur receive karna.
SDLC HDLC (High-level Data Link Control) ka base protocol hai.
Key Features of SDLC
-> Bit-oriented protocol – Data ko bits ke continuous stream mein bhejta hai
-> Synchronous mode – Sender aur Receiver ke beech timing (clock) same hoti hai
-> Error detection ke liye CRC ka use hota hai
-> Full-duplex communication support karta hai (dono taraf se ek saath data exchange ho sakta hai)
-> Point-to-point aur multipoint link dono support karta hai
SDLC Frame ke Parts
Ek SDLC frame ke different fields hote hain:
| Field | Kya Kaam Hai? |
|---|---|
| Flag | Frame ka start aur end batata hai (01111110) |
| Address | Kis receiver (station) ko data bhejna hai, uska address hota hai |
| Control | Batata hai frame ka type (Information, Supervisory, Unnumbered) |
| Information | Actual data jo bhejna hai |
| FCS (CRC) | Error checking bits |
| Flag | Frame ka end (same as starting flag) |
SDLC Frame Format
Types of Frames
1. Information Frames (I-Frames) – Data bhejne ke liye
2. Supervisory Frames (S-Frames) – Flow control aur error control ke liye (ACK/NACK)
3. Unnumbered Frames (U-Frames) – Control kaam ke liye (link establish ya disconnect karne ke liye)
Modes of Communication
1. Normal Response Mode (NRM)
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Primary station control karta hai.
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Secondary station sirf tab data bhej sakta hai jab primary allow kare.
2. Asynchronous Balanced Mode (ABM)
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Dono stations equal hote hain, dono kabhi bhi data bhej sakte hain.
3. Asynchronous Response Mode (ARM)
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NRM jaise hi hai, par secondary kabhi-kabhi bina permission ke bhi data bhej sakta hai.
Example
Station A (Primary) ko Station B (Secondary) ko “HELLO” bhejna hai.
Frame kuch aisa hoga:
Receiver (B) data check karega (error ke liye FCS ka use hoga) aur ACK bhej dega.
Communication Diagram
Advantages
-> Reliable data transfer
-> Synchronous link par efficient kaam karta hai
-> Point-to-point aur multipoint dono support karta hai
Disadvantages
-> Purana protocol hai, ab zyada use nahi hota
-> Synchronization ka extra overhead hota hai
Summary Table
| Feature | SDLC |
|---|---|
| Developed By | IBM |
| Type | Bit-oriented protocol |
| Layer | Data Link Layer |
| Modes | NRM, ABM, ARM |
| Frame Types | I-Frame, S-Frame, U-Frame |
| Basis For | HDLC aur modern protocols |