What is the TCP/IP model?

The TCP/IP model is a practical network model that describes how devices interact on the internet and in networks using the TCP/IP protocol stack.

Short formulation for an interview:

TCP/IP is a four-layer model that underlies the internet. It describes how data is created by an application, packaged into TCP/UDP segments, placed into IP packets, turned into frames, and transmitted over the network.

The TCP/IP model is more realistic and practical than OSI - it is the one actually used in modern networks.

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#4 layers of the TCP/IP model

The TCP/IP model consists of four layers, each responsible for specific tasks and protocols.

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#1. Application Layer

Combines OSI layers 5-7.

Functions:

• network services for applications
• application-layer protocols

Protocols:

• HTTP/HTTPS
• DNS
• DHCP
• FTP/SFTP
• SMTP/IMAP/POP3
• SSH
• SNMP

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#2. Transport Layer

Equivalent to OSI layer 4.

Functions:

• delivering data between hosts
• segmentation
• flow control
• reliability (or the lack of it)

Protocols:

• TCP - reliable transmission
• UDP - fast, without guarantees

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#3. Internet Layer

Equivalent to OSI layer 3.

Functions:

• IP addressing
• routing
• path selection
• IP packet fragmentation

Protocols:

• IPv4 / IPv6
• ICMP / ICMPv6
• ARP / NDP (sometimes classified here)
• OSPF, BGP, RIP - routing protocols

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#4. Network Access Layer

Combines OSI layers 1 and 2.

Functions:

• transmitting frames over the physical medium
• MAC addressing
• working with cables, connectors, signals

Protocols and technologies:

• Ethernet
• Wi-Fi (802.11)
• PPP
• VLAN
• DSL, DOCSIS
• physical standards (UTP, fiber optics)

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#How data passes through the TCP/IP layers (encapsulation)

1. Application: HTTP creates the data
2. Transport: TCP turns it into segments
3. Internet: IPv4/IPv6 packages the segments into packets
4. Network Access: Ethernet turns the packet into a frame
5. Frame → bits → signal → sent to the network

On the receiving side, the process happens in reverse order.

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#Comparison of the TCP/IP and OSI models

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Main differences:

• TCP/IP is practical → OSI is theoretical
• TCP/IP has 4 layers → OSI has 7
• TCP/IP has no separate Presentation and Session layers

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#Why TCP/IP is used

Advantages:

• flexibility
• scalability
• matches the internet's actual protocols
• used in operating systems
• suitable for all types of networks

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#Ready answer for an interview

The TCP/IP model is a four-layer model of network interaction that underlies the internet. Layers: Application, Transport, Internet, Network Access. It describes how data travels from applications to the physical medium using the TCP, UDP, IP, Ethernet, and other protocols. TCP/IP is the practical model that runs the entire internet.

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#Cheat sheet (5 seconds)

• TCP/IP = Application, Transport, Internet, Network Access
• A practical model (unlike OSI)
• Main protocols: TCP, UDP, IP, ICMP, DNS, HTTP, Ethernet
• The TCP/IP stack forms the foundation of the network and the internet