Network Protocols in High Level Design (HLD)

In distributed systems, services do not exist in isolation. They communicate across networks.
The rules governing how data is transmitted between systems are called network protocols.

A network protocol defines:

• How data is formatted
• How messages are transmitted
• How errors are handled
• How connections are established and terminated

In High Level Design, selecting the correct protocol directly affects:

Real World Analogy

Think of network protocols like languages used by different departments in a company.

Each protocol serves a different communication need.

Network Protocol Stack

Protocols operate in layers. The most common model used in system design is the TCP/IP model.

Each layer has a responsibility.

1 Transport Layer Protocols

Transport protocols determine how data travels between services.

The two primary transport protocols are:

TCP (Transmission Control Protocol)

TCP is a connection-oriented protocol that guarantees delivery.

Features:

• Reliable delivery
• Ordered packets
• Retransmission
• Flow control
• Congestion control

TCP Connection Lifecycle

TCP uses a three-way handshake.

Connection established.

TCP Data Transfer

If packet is lost → TCP retransmits.

When TCP Is Used

TCP is used when data correctness is critical.

Examples:

UDP (User Datagram Protocol)

UDP is connectionless and faster than TCP.

Characteristics:

• No connection setup
• No guaranteed delivery
• No ordering
• Minimal overhead

UDP Data Flow

No acknowledgments.

Packets may:

• arrive out of order
• get lost
• be duplicated

When UDP Is Used

UDP is ideal for real-time communication.

Examples:

Application Layer Protocols

Application layer protocols define how applications communicate.

Common protocols:

HTTP (HyperText Transfer Protocol)

HTTP is the foundation of the web.

It follows a request-response model.

Example request:

GET /users HTTP/1.1
Host: api.example.com

Example response:

HTTP/1.1 200 OK
Content-Type: application/json

HTTP Characteristics

HTTP Methods

Example:

fetch("https://api.example.com/users")

HTTPS (HTTP Secure)

HTTPS is HTTP over TLS encryption.

It ensures:

• Encryption
• Integrity
• Authentication

Architecture:

Benefits:

WebSocket

WebSocket enables persistent bidirectional communication.

Unlike HTTP:

• Connection stays open
• Server can push data
• Real-time communication

WebSocket Flow

WebSocket Use Cases

JavaScript WebSocket Example

const socket = new WebSocket("wss://example.com/socket");
 
socket.onopen = () => {
  socket.send("Hello Server");
};
 
socket.onmessage = (event) => {
  console.log("Received:", event.data);
};

gRPC

gRPC is a high-performance RPC framework developed by Google.

Uses:

• HTTP/2
• Protocol Buffers
• Binary serialization

gRPC Architecture

Why gRPC Is Fast

gRPC vs REST

DNS (Domain Name System)

DNS translates domain names into IP addresses.

Example:

google.com → 142.250.190.14

DNS Resolution Flow

SMTP (Email Protocol)

SMTP is used for sending emails.

Architecture:

Protocol Selection in System Design

Choosing the right protocol depends on system requirements.

Protocols in Microservices Architecture

Protocols used:

Protocol Performance Comparison

Real World Architecture Example

Example: YouTube streaming system

Protocols used:

Key Takeaways

• Network protocols define how services communicate across networks
• TCP ensures reliable delivery, while UDP prioritizes speed
• HTTP/HTTPS power most web APIs
• WebSocket enables real-time communication
• gRPC is widely used in microservices architectures
• DNS resolves domain names to IP addresses
• Choosing the correct protocol is critical for performance, scalability, and reliability

Understanding network protocols is fundamental to designing large-scale distributed systems.