Complete Distribution of the TCP/IP Protocol Suite in the OSI Model — Understanding Network Protocols at a Glance

February 24, 2015 Networking Tcp-Ip, Osi, Networking, Protocol 2059 words 10 min read

Network communication is the cornerstone of modern information technology, and understanding how network protocols work is crucial for every developer and system administrator. This article uses the OSI model framework to provide a detailed introduction to the distribution and roles of each protocol in the TCP/IP protocol suite within the network layer hierarchy.

What is the OSI Model?

The OSI (Open Systems Interconnection) model is a conceptual network model that divides the network communication process into seven layers. Although this model is less popular in practice than the TCP/IP model, it is very helpful for understanding how network protocols work.

The OSI seven-layer model includes:

Physical Layer: Transmits raw bit streams
Data Link Layer: Provides reliable communication between nodes
Network Layer: Responsible for routing and forwarding
Transport Layer: Provides end-to-end communication
Session Layer: Manages session connections
Presentation Layer: Data format conversion and encryption
Application Layer: User interface and application protocols

What is the TCP/IP Protocol Suite?

The TCP/IP (Transmission Control Protocol/Internet Protocol) protocol suite is the foundational protocol collection of the Internet. It is more concise and practical than the OSI model. The TCP/IP protocol suite is typically divided into four layers:

Application Layer
Transport Layer
Network Layer
Network Interface Layer

Distribution of the TCP/IP Protocol Suite in the OSI Model

Below is the complete distribution diagram of each protocol in the TCP/IP protocol suite across the OSI model:

mermaid
flowchart TD
    classDef app fill:#e3f2fd,stroke:#1976d2,stroke-width:2px
    classDef pres fill:#e8f5e9,stroke:#4caf50,stroke-width:2px
    classDef sess fill:#fff3e0,stroke:#ff9800,stroke-width:2px
    classDef trans fill:#f3e5f5,stroke:#9c27b0,stroke-width:2px
    classDef net fill:#fce4ec,stroke:#e91e63,stroke-width:2px
    classDef data fill:#ffebee,stroke:#f44336,stroke-width:2px
    classDef phys fill:#efebe9,stroke:#795548,stroke-width:2px
    
    subgraph "Application Layer"
        A1@{ shape: rounded, label: "HTTP" }:::app
        A2@{ shape: rounded, label: "FTP" }:::app
        A3@{ shape: rounded, label: "SMTP" }:::app
        A4@{ shape: rounded, label: "TELNET" }:::app
        A5@{ shape: rounded, label: "POP3" }:::app
        A6@{ shape: rounded, label: "IMAP4" }:::app
        A7@{ shape: rounded, label: "DNS" }:::app
        A8@{ shape: rounded, label: "DHCP" }:::app
        A9@{ shape: rounded, label: "NFS" }:::app
        A10@{ shape: rounded, label: "SNMP" }:::app
    end
    subgraph "Presentation Layer"
        B1@{ shape: rounded, label: "SSL/TLS" }:::pres
        B2@{ shape: rounded, label: "LDAP" }:::pres
        B3@{ shape: rounded, label: "RPC" }:::pres
    end
    subgraph "Session Layer"
        C1@{ shape: rounded, label: "RPC" }:::sess
        C2@{ shape: rounded, label: "NetBIOS" }:::sess
        C3@{ shape: rounded, label: "SMB" }:::sess
    end
    subgraph "Transport Layer"
        D1@{ shape: rounded, label: "TCP Transmission Control Protocol" }:::trans
        D2@{ shape: rounded, label: "UDP User Datagram Protocol" }:::trans
    end
    subgraph "Network Layer"
        E1@{ shape: rounded, label: "IP" }:::net
        E2@{ shape: rounded, label: "ICMP" }:::net
        E3@{ shape: rounded, label: "IGMP" }:::net
        E4@{ shape: rounded, label: "OSPF" }:::net
        E5@{ shape: rounded, label: "RIP" }:::net
        E6@{ shape: rounded, label: "BGP" }:::net
        E7@{ shape: rounded, label: "ARP" }:::net
    end
    subgraph "Data Link Layer"
        F1@{ shape: rounded, label: "Ethernet" }:::data
        F2@{ shape: rounded, label: "PPP" }:::data
        F3@{ shape: rounded, label: "HDLC" }:::data
        F4@{ shape: rounded, label: "Frame Relay" }:::data
        F5@{ shape: rounded, label: "ATM" }:::data
    end
    subgraph "Physical Layer"
        G1@{ shape: rounded, label: "IEEE 802.3" }:::phys
        G2@{ shape: rounded, label: "RS-232" }:::phys
        G3@{ shape: rounded, label: "V.35" }:::phys
        G4@{ shape: rounded, label: "RJ-45" }:::phys
    end

Detailed Protocol Descriptions by Layer

Application Layer Protocols

The application layer is the highest layer of the OSI model, directly serving user applications. The following are the major protocols:

HTTP/HTTPS (Hypertext Transfer Protocol)

Purpose: Communication between web browsers and servers
Port: 80 (HTTP), 443 (HTTPS)
Characteristics: Request-response based, stateless protocol

FTP (File Transfer Protocol)

Purpose: Transferring files between client and server
Port: 20 (data), 21 (control)
Characteristics: Supports file upload, download, and deletion

SMTP (Simple Mail Transfer Protocol)

Purpose: Sending email
Port: 25
Characteristics: Dedicated to mail transport, typically used in conjunction with POP3/IMAP4

TELNET (Teletype Network)

Purpose: Remote login service
Port: 23
Characteristics: Unencrypted remote connection protocol

POP3 (Post Office Protocol 3)

Purpose: Receiving email from a mail server
Port: 110
Characteristics: After the client downloads emails from the server, emails are typically deleted

IMAP4 (Internet Message Access Protocol 4)

Purpose: Accessing and managing email on a mail server
Port: 143
Characteristics: Supports managing email on the server without necessarily downloading locally

DNS (Domain Name System)

Purpose: Resolving domain names to IP addresses
Port: 53
Characteristics: Distributed naming system, foundational infrastructure of the Internet

DHCP (Dynamic Host Configuration Protocol)

Purpose: Automatically assigning IP addresses to network devices
Port: 67 (server), 68 (client)
Characteristics: Simplifies network management, supports dynamic IP address allocation

NFS (Network File System)

Purpose: Sharing file systems over a network
Port: 2049
Characteristics: Allows users to access remote files as if they were local

SNMP (Simple Network Management Protocol)

Purpose: Network device management and monitoring
Port: 161 (manager), 162 (agent)
Characteristics: Used for collecting and configuring network device information

Presentation Layer Protocols

The presentation layer is responsible for data format conversion, encryption, and compression.

SSL/TLS (Secure Sockets Layer/Transport Layer Security)

Purpose: Provides secure communication channels
Characteristics: Supports data encryption, authentication, and data integrity protection
Applications: HTTPS, SMTPS, IMAPS and other secure protocols

LDAP (Lightweight Directory Access Protocol)

Purpose: Accessing and maintaining directory services
Port: 389 (plaintext), 636 (encrypted)
Characteristics: Used for user authentication, address lookup, and other services

RPC (Remote Procedure Call)

Purpose: Allows programs to call procedures on other computers
Characteristics: Transparent remote procedure calls that hide network communication details

Session Layer Protocols

The session layer is responsible for establishing, managing, and terminating session connections.

RPC (Remote Procedure Call)

Purpose: Provides remote procedure call services at the session layer
Characteristics: Manages session state for remote calls

NetBIOS (Network Basic Input/Output System)

Purpose: Provides network name services and session services
Port: 137-139
Characteristics: Primarily used in early Windows network environments

SMB (Server Message Block)

Purpose: Sharing files, printers, and serial ports between computers
Port: 445
Characteristics: Modern versions of SMB support encryption and authentication

Transport Layer Protocols

The transport layer provides end-to-end communication services, ensuring reliable data transmission.

TCP (Transmission Control Protocol)

Purpose: Provides reliable, connection-oriented data transmission
Characteristics:
- Connection-oriented communication
- Packet ordering and acknowledgment
- Flow control and congestion control
- Reliable data transmission

TCP Connection Establishment (Three-way Handshake):

Client sends SYN packet
Server sends SYN-ACK packet
Client sends ACK packet

TCP Connection Termination (Four-way Handshake):

Client sends FIN packet
Server sends ACK packet
Server sends FIN packet
Client sends ACK packet

UDP (User Datagram Protocol)

Purpose: Provides unreliable, connectionless data transmission
Characteristics:
- Connectionless communication
- No guarantee of packet order or reliability
- Low overhead, high transmission efficiency
- Suitable for real-time applications

TCP vs UDP Comparison:

Feature	TCP	UDP
Connection	Connection-oriented	Connectionless
Reliability	Reliable transmission	Unreliable transmission
Ordering	Guaranteed order	No order guarantee
Speed	Slower	Faster
Overhead	Higher	Lower
Use Cases	File transfer, web browsing	Real-time video, online gaming

Network Layer Protocols

The network layer is responsible for packet routing and forwarding, serving as the core layer of the entire network.

IP (Internet Protocol)

Purpose: Transmits packets across networks
Characteristics:
- Connectionless transmission service
- Provides logical addressing (IP addresses)
- Responsible for packet routing decisions
- Supports IPv4 and IPv6

IP Packet Structure:

Version
Header length
Type of service
Total length
Identification
Flags and fragment offset
TTL (Time to Live)
Protocol number
Header checksum
Source IP address
Destination IP address

ICMP (Internet Control Message Protocol)

Purpose: Provides feedback about network conditions
Characteristics:
- Used for network diagnostics and error reporting
- Supports the ping command
- Supports path discovery

Common ICMP Message Types:

Echo Request/Reply (ping)
Destination Unreachable
Time Exceeded
Parameter Problem

IGMP (Internet Group Management Protocol)

Purpose: Manages multicast group membership
Characteristics:
- Used for IP multicast
- Manages multicast routers
- Controls multicast group members

OSPF (Open Shortest Path First)

Purpose: Interior gateway routing protocol
Characteristics:
- Based on Dijkstra’s algorithm
- Supports area partitioning
- Fast convergence
- Loop-free routing

RIP (Routing Information Protocol)

Purpose: Distance-vector routing protocol
Characteristics:
- Simple and easy to use
- Uses hop count as metric
- Maximum hop count of 15
- Slower convergence

BGP (Border Gateway Protocol)

Purpose: Exterior gateway routing protocol
Characteristics:
- Rich routing policies
- Supports large-scale networks
- Path-vector based
- Core protocol of the Internet

ARP (Address Resolution Protocol)

Purpose: Resolves IP addresses to MAC addresses
Characteristics:
- Operates at the data link layer
- Uses broadcast messages
- Builds and maintains ARP cache tables

Data Link Layer Protocols

The data link layer is responsible for providing reliable data transmission over physical networks.

Ethernet

Purpose: LAN communication standard
Characteristics:
- Uses CSMA/CD protocol
- Supports multiple transmission rates
- Widely used in local area networks

PPP (Point-to-Point Protocol)

Purpose: Point-to-point communication protocol
Characteristics:
- Used for serial connections
- Supports multiple network layer protocols
- Provides authentication

HDLC (High-Level Data Link Control)

Purpose: Bit-oriented data link layer protocol
Characteristics:
- Suitable for wide area networks
- Supports full-duplex communication
- Provides frame synchronization

Frame Relay

Purpose: Packet-switched WAN technology
Characteristics:
- Based on virtual circuits
- Efficient data transmission
- Simplified network management

ATM (Asynchronous Transfer Mode)

Purpose: High-speed data transmission technology
Characteristics:
- Uses fixed-length cells
- Supports multiple service types
- Suitable for multimedia transmission

Physical Layer Protocols

The physical layer is responsible for transmitting raw bit streams and is the lowest layer of network communication.

IEEE 802.3

Purpose: Ethernet physical layer standard
Characteristics:
- Defines physical layer specifications
- Supports multiple transmission media
- Includes twisted pair, fiber optic, etc.

RS-232

Purpose: Serial communication standard
Characteristics:
- Supports point-to-point connections
- Asynchronous communication
- Widely used for device connections

V.35

Purpose: Broadband data transmission interface standard
Characteristics:
- Supports high-speed data transmission
- Primarily used for WAN connections
- Standardized interface specification

RJ-45

Purpose: Network connector standard
Characteristics:
- 8-pin connector
- Used for Ethernet connections
- Supports twisted pair connections

Protocol Communication Examples

Web Access Process

How do protocols at each layer work together when you visit a website?

Application Layer: Browser initiates an HTTP request
Presentation Layer: If using HTTPS, SSL/TLS encrypts the data
Session Layer: Establishes and manages session connections
Transport Layer: TCP protocol ensures reliable data transmission
Network Layer: IP protocol handles packet routing and forwarding
Data Link Layer: Ethernet protocol transmits data within the LAN
Physical Layer: Transmits bit streams through physical media

Email Sending Process

When sending an email:

Application Layer: MUA (Mail User Agent) sends email via SMTP
Transport Layer: TCP ensures reliable transmission of email data
Network Layer: IP protocol routes email data to the target server
Data Link Layer: Transmits data packets across the network
Physical Layer: Transmits data through the physical network

Common Network Troubleshooting

Using the ping Command

bash
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# Test network connectivity
ping 8.8.8.8

# Specify number of pings
ping -c 4 8.8.8.8

# Specify packet size
ping -s 1024 8.8.8.8

traceroute Path Tracing

bash
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# Linux/macOS
traceroute 8.8.8.8

# Windows
tracert 8.8.8.8

netstat Network Status

bash
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# View all network connections
netstat -an

# View listening ports
netstat -ltn

# View network statistics
netstat -s

tcpdump Packet Analysis

bash
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# Capture traffic on a specific port
tcpdump -i any port 80

# Save captured packets
tcpdump -w capture.pcap

# Read captured packets
tcpdump -r capture.pcap

Network Security Considerations

Firewall Configuration

bash
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# Check firewall status
sudo ufw status

# Allow a specific port
sudo ufw allow 22/tcp
sudo ufw allow 80/tcp

# Deny a specific port
sudo ufw deny 443/tcp

SSL/TLS Configuration

bash
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# Generate private key and certificate
openssl genrsa -out server.key 2048
openssl req -new -x509 -key server.key -out server.crt -days 365

# View certificate information
openssl x509 -in server.crt -text

Summary

Through this article, we have gained a detailed understanding of the complete distribution of the TCP/IP protocol suite within the OSI model. Understanding the protocols at each layer and their roles is crucial for network troubleshooting, performance optimization, and security management.

Key Takeaways:

The OSI Model provides a conceptual framework for network communication, helping to understand the functions and responsibilities of each layer
The TCP/IP Protocol Suite is the practically applied protocol collection, more practical than the OSI model
Protocol layering makes network design more modular, facilitating development and maintenance
Protocols at each layer have clear responsibilities and collaborate to accomplish network communication
In practice, appropriate protocols and technologies need to be selected based on specific requirements

With the rapid development of cloud computing, IoT, and 5G technologies, network protocols continue to evolve. A deep understanding of how network protocols work will help us better address future technical challenges and build more secure and efficient network infrastructure.

Whether you are a developer, system administrator, or network engineer, mastering network protocol knowledge is an essential skill. We hope this article helps you build a solid foundation in networking theory and provides strong support for your career development.