What Is TCP/IP?

• 2018/08/30

What is TCP/IP?

• A collective term for communication protocols.
• It is the de facto standard.
• A protocol is essentially an agreement that lets computers talk to each other over a network.

OSI reference model

The OSI model defines seven layers that behave like independent modules:

• Application layer
• Presentation layer
• Session layer
• Transport layer
• Network layer
• Data link layer
• Physical layer

In the TCP/IP model:

• The application layer covers everything down through the OSI session layer.
• The transport layer matches the OSI transport layer.
• The internet layer matches the network layer.
• The link layer corresponds to the data link + physical layers.

TCP (Transmission Control Protocol)

• Maps to the transport layer in the OSI model.
• Connection-oriented and guarantees delivery between the two endpoints.
• UDP (User Datagram Protocol) is connectionless and does not promise delivery.

IP (Internet Protocol)

• Maps to the network layer in the OSI model.
• Sends packets across networks.

Protocols worth memorizing

• SSH (Secure Shell) → Application layer
• HTML (HyperText Markup Language)
• HTTP (HyperText Transfer Protocol) → Session layer
• FTP (File Transfer Protocol) → Session layer
• SMTP (Simple Mail Transfer Protocol) → Session layer
• POP3 (Post Office Protocol v3) → Session layer
• IMAP (Internet Message Access Protocol) → Session layer
• TCP, UDP → Transport layer
• SSL (Secure Sockets Layer) → Transport layer
• IP → Network layer
• Ethernet → Data link layer
• ARP (Address Resolution Protocol) → Data link layer

Funny enough, HTML counts as a protocol too.

Closing

Knowing these fundamentals expands your options when you design infrastructure or architecture.

Reference

• Mastering TCP/IP, Introductory Edition — the canonical starter book.