Complete Computer Networks Notes for GATE CSE 2026 – Best Notes

Computer Networks GATE CSE ka sabse zyada search hone wala subject hai. Har saal 4-6 marks aate hain. Isme IP Addressing, TCP/UDP aur Routing Algorithms se direct numerical aate hain. Ye notes PYQ analysis se banaye gaye hain.

1. OSI and TCP/IP Model – Base

OSI Model 7 Layers: Physical, Data Link, Network, Transport, Session, Presentation, Application. Yaad karne ki Trick: All People Seem To Need Data Processing. GATE me kaunsa protocol kis layer par hai ye poochte hain.

Physical: Bits, Hub, Repeater
Data Link: Frames, Switch, MAC Address, CSMA/CD
Network: Packets, Router, IP Address
Transport: Segments, Port Number, TCP/UDP
Application: HTTP, FTP, DNS, SMTP

TCP/IP Model: 4 Layers (Network Access, Internet, Transport, Application). Real Internet isi par chalta hai.

2. IP Addressing and Subnetting – Har Saal 2 Marks

IPv4 32-bit ka hota hai. 2^p hosts, 2^p -2 usable hosts (Network aur Broadcast hata ke).

Classful: Class A (0-127), B (128-191), C (192-223). Class A me N=8,H=24. Class B me N=16,H=16. Class C me N=24,H=8.

Subnetting: Host ID se bits leke Subnet ID banate hain. Formula: Number of Subnets = 2^n, Hosts per Subnet = 2^h -2. Subnet Mask: Network bits 1, Host bits 0.

Supernetting/CIDR: Subnetting ka ulta. Multiple Networks ko ek me jodna. CIDR notation: 192.168.1.0/24 matlab 24 bits Network ke.

GATE Trick: 192.168.1.5/30 me kitne hosts? /30 matlab 32-30=2 host bits, 2^2-2=2 hosts. Is type ke numerical har saal aate hain. Private IP: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.

3. Routing Algorithms

Distance Vector (Bellman-Ford): Har router apne neighbor ko apna Routing Table bhejta hai. Count to Infinity Problem hota hai. Solution: Split Horizon.

Link State (Dijkstra): Har router pure network ko apna Link State bhejta hai. OSPF is par kaam karta hai. Fast aur No Loop.

Protocols: RIP (Distance Vector, Hop Count 15 max), OSPF (Link State), BGP (Path Vector).

4. Transport Layer – TCP vs UDP – Most Important

UDP: Connectionless, Unreliable, No Flow Control, Fast. Header 8 Byte. Video Streaming, DNS, DHCP me use hota hai.

TCP: Connection Oriented, Reliable, Flow Control + Congestion Control. Header 20 Byte minimum. 3-Way Handshake: SYN, SYN-ACK, ACK.

Flow Control: Receiver kitna data le sakta hai. Sliding Window Protocol, Go-Back-N aur Selective Repeat.

Go-Back-N: Window Size = 2^m -1. Agar ek packet loss to pura window dubara bhejta hai.
Selective Repeat: Window Size = 2^(m-1). Sirf loss wala packet bhejta hai. Efficient hai.

Congestion Control: Slow Start, AIMD, Fast Retransmit. Congestion Window (cwnd) ka concept.

GATE Formula: Efficiency = (Window Size * Transmission Time) / (Transmission Time + 2*Propagation Time). Utilization nikalna har saal aata hai.

5. Application Layer and Others

DNS: Domain Name ko IP me convert karta hai. Port 53. UDP use karta hai.

HTTP: Port 80, Persistent aur Non-Persistent. HTTPS Port 443.

SMTP/POP: Email ke liye. SMTP Port 25.

CSMA/CD: Data Link Layer me Collision Detection. Efficiency = 1 / (1 + 6.44*a) jahan a = Tp/Tt. CSMA/CA Wifi me use hota hai.

Final Checklist: Subnetting Numerical, TCP Flow Control Window Size, Distance Vector vs Link State, TCP vs UDP Difference. Ye 4 pakka kar lo to 5 marks pakke.

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Computer Networks Notes for GATE CSE