Physical Layer in Computer Networks

Physical Layer Kya Hai?

Physical Layer, OSI model ki sabse neeche wali (1st) layer hoti hai.

Iska main kaam:

Data ko signal ke form mein ek device se doosre device tak physically bhejna — chahe wo wire se ho, fiber optic cable se, ya wireless signal se.

Physical Layer Kya-Kya Karti Hai?

Yeh layer sirf 0 aur 1 (bits) ko electrical ya optical signals mein badal kar bhejti hai. Isse data ka matlab nahi samajh aata — iska kaam sirf “data bhejna” hota hai.

Physical Layer ke Important Kaam:

Kaam	Asaan Explanation
Bit Transmission	0s aur 1s ko signals mein convert karna
Data Rate Control	Kitni speed se data bhejna hai (Mbps, Gbps)
Topology Decide Karna	Devices ka layout (Star, Bus, etc.)
Transmission Medium	Kaunsa wire ya wireless system use hoga
Synchronization	Sender aur receiver same speed pe kaam karein
Line Configuration	Devices kaise connected hain (Point to Point ya Multipoint)
Modulation	Zarurat ho to digital data ko analog signal mein badalna

Physical Layer Par Data Kaise Dikhta Hai?

Upper layers se data binary form mein aata hai:

Physical layer ko sirf bits se matlab hota hai, meaning se nahi.

Diagram – OSI Model Aur Physical Layer

Physical Layer Kaunse Medium Use Karti Hai?

Medium Type	Kya Hota Hai
Copper Cable	LAN wires – electric signals bhejte hain
Fiber Optic	Internet cables – light signals use hote hain
Wireless	Wi-Fi, Bluetooth, 4G – radio waves use hote hain

Real-Life Example

Maan lijiye aap “Hi” likh ke bhej rahe ho internet pe:

“Hi” → 01001000 01101001 (binary bits)
Yeh bits Physical Layer tak jaate hain
Yeh bits ban jaate hain:
- Electricity (wired)
- Light pulses (fiber)
- Radio signals (Wi-Fi)
Receiver in signals ko wapas bits mein badalkar upper layers ko bhejta hai

Devices Jo Physical Layer Pe Kaam Karte Hain

Device	Use
Hub	Sabhi devices ko bits forward karta hai
Repeater	Weak signal ko strong karta hai
Cables	Signal bhejne ka rasta
NIC (Network Card)	Signal send/receive karta hai
Modem	Digital signal ko analog mein aur wapas convert karta hai

Physical Layer Se Jude Important Terms

Term	Kya Matlab Hai
Baud Rate	Kitne signal changes per second hote hain
Bandwidth	Max data speed jo medium handle kar sakta hai
Latency	Signal bhejne mein lagne wala delay
Attenuation	Signal ka distance ke saath weak ho jaana

Summary

Physical Layer = OSI Model ki pehli layer
Sirf bits ko signal mein badalti hai aur bhejti hai
Use karti hai: wires, fiber optics, wireless
Devices: Hub, NIC, Modem, Repeater
Is layer ko data ke meaning se koi lena dena nahi hota

The Hingineer