TCP/IP Model
The TCP/IP model is the practical networking model that powers the internet. It has 4 layers and maps to the OSI model's 7 layers. Developed by DARPA in the 1970s.
Application Layer
PDU: Data / MessageMaps to: Application + Presentation + Session (OSI 5,6,7)
Protocols
Description
Combines OSI's top 3 layers. Handles all high-level protocols, data representation and session management.
Transport Layer
PDU: Segment / DatagramMaps to: Transport (OSI 4)
Protocols
Description
Provides end-to-end communication. TCP offers reliable, ordered delivery. UDP offers fast, connectionless delivery.
Internet Layer
PDU: PacketMaps to: Network (OSI 3)
Protocols
Description
Handles logical addressing and routing of packets across multiple networks using IP addresses.
Network Access Layer
PDU: Frame / BitsMaps to: Data Link + Physical (OSI 1,2)
Protocols
Description
Combines OSI's bottom 2 layers. Handles physical transmission and local network addressing.
TCP 3-Way Handshake
SYN
Client → Server
Client sends SYN (synchronize) to initiate connection
SYN-ACK
Server → Client
Server acknowledges with SYN-ACK (synchronize-acknowledge)
ACK
Client → Server
Client sends ACK — connection established!
Key Questions
Q: How many layers does TCP/IP have?
4 layers: Application, Transport, Internet, Network Access
Q: What is the difference between TCP and UDP?
TCP is connection-oriented, reliable, ordered. UDP is connectionless, faster, no guarantee.
Q: What does IP stand for?
Internet Protocol — handles logical addressing and routing
Q: What is a 3-way handshake?
TCP connection setup: SYN → SYN-ACK → ACK