TCP/IP Application layer maps to which OSI layers?
Application + Presentation + Session (top 3)
TCP/IP Network Access maps to which OSI layers?
Data Link + Physical (bottom 2)
TCP/IP Internet layer corresponds to which OSI layer?
Network (Layer 3)
TCP/IP Transport maps to which OSI layer(s)?
Transport only (1-to-1)
The merge pattern of OSI→TCP/IP from top to bottom is?
3 → 1 → 1 → 2
Which layer uses port numbers?
Transport layer
Which layer uses IP addresses and routing?
Internet layer
Which layer uses MAC addresses and framing?
Network Access layer
Data unit at Transport (TCP)?
Segment
Data unit at Internet layer?
Packet
Data unit at Network Access layer?
Frame (then bits)
Name two Transport-layer protocols.
TCP and UDP
Name three Application-layer protocols.
HTTP, FTP, SMTP (also DNS, HTTPS)
What is encapsulation?
Each layer wrapping the data above it in its own header as it moves down the stack
Why does TCP/IP merge OSI's top 3 layers?
In practice the application handles session/presentation duties itself, so they need no separate layers
Recall Feynman: explain to a 12-year-old
Sending a letter has steps: you write it (your message), put it in an envelope with the person's name (so it reaches the right person = ports/Transport), write the city & street address (so the mail system routes it = IP/Internet), and finally a truck physically drives it on roads (the wires/WiFi = Network Access). The TCP/IP model is just these 4 steps. OSI is the same idea but breaks "write the letter" into 3 tinier steps and "drive it" into 2 — so 7 boxes instead of 4. Same journey, just chopped differently.
Dekho, internet ko sirf paper pe nahi, real hardware pe chalna tha — isliye jo model actually internet chala raha hai woh hai TCP/IP model with 4 layers. OSI model textbook wala reference hai jisme 7 layers hote hain. Dono same kaam karte hain — data ko ek computer se doosre tak pohanchana — bas OSI ne chhote-chhote tukdo me toda hai, TCP/IP ne unko merge karke 4 hi rakha.
Mapping yaad rakhne ka simplest tareeka: pattern 3-1-1-2 (upar se neeche). Matlab TCP/IP ka Application layer = OSI ke top 3 (Application + Presentation + Session) kyunki real life me application khud hi session aur formatting handle kar leti hai. Phir Transport = Transport (one-to-one), Internet = Network (sirf naam alag, kaam wahi — IP aur routing), aur Network Access = Data Link + Physical (bottom 2, jahan actual bits wire/WiFi pe jaate hain).
Layers ka kaam yaad rakho function se: Transport me port numbers (sahi program tak pohanchao — TCP/UDP), Internet me IP address aur routing (sahi computer dhoondo), Network Access me MAC address aur framing (physically agle hop tak bhejo). Aur data ka naam har layer pe badalta hai — Transport pe segment, Internet pe packet, Network Access pe frame. Exam me ye precision marks dilati hai.
Ek common galti: agar question bole "TCP/IP model" toh answer 4 layers hai. Kuch books 5-layer hybrid sikhati hain (Network Access ko Data Link + Physical me todke) — woh teaching ke liye hai, original TCP/IP toh 4 hi hai. Aur "Internet layer" ko app/browsing samajhne ki galti mat karna — woh OSI Network layer hai, routing ka kaam.
