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Computer Network Structure and Architecture

1. Introduction

A computer network consists of interconnected computers, communication devices and transmission links that allow computers to exchange data and share resources.

To understand how a network works, we study its structure and architecture.

  • Network Structure → describes the physical and functional components of a network and how they are organized.
  • Network Architecture → defines the rules, layers, protocols and standards used for communication between network devices.

2. Computer Network Structure

The basic structure of a computer network can be represented as:

       Computer A
            |
            |
       Network Device
        (Switch/Router)
            |
      Communication
          Network
            |
       Network Device
            |
            |
       Computer B

A network mainly consists of the following components.

1. End Devices / Hosts

These are devices that send or receive data.

Examples:

  • Desktop computers
  • Laptops
  • Smartphones
  • Servers
  • Printers
  • IoT devices

They are also called hosts or end systems.

2. Communication Links

Communication links provide the path through which data travels.

They can be:

Wired

  • Twisted-pair cable
  • Coaxial cable
  • Optical fiber

Wireless

  • Radio waves
  • Microwave
  • Infrared

For example:

Computer A ===== Cable ===== Computer B

3. Networking Devices

Networking devices connect computers and networks.

Important devices include:

DeviceMain Function
HubConnects multiple devices and broadcasts data
SwitchConnects devices within a LAN and forwards frames
RouterConnects different networks and forwards packets
BridgeConnects network segments
GatewayConnects networks using different protocols
Access PointProvides wireless network access
ModemConverts signals for communication over certain access networks

4. Network Software

Network hardware needs software to control communication.

Examples include:

  • Network operating systems
  • Network protocols
  • Device drivers
  • Network management software
  • Security software

3. Types of Network Structure

Networks can be organized in different ways.

A. Client-Server Structure

In this structure, a server provides services to clients.

             SERVER
                |
       -------------------
       |        |        |
    Client   Client   Client

Example:

A college server stores student records, while computers in different departments access those records.

Advantages:

  • Centralized management
  • Better security
  • Easy backup
  • Centralized data storage

B. Peer-to-Peer Structure

In a Peer-to-Peer (P2P) network, computers can communicate directly with each other.

       Computer A
        /       \
       /         \
Computer B ----- Computer C

Each computer can act as both a client and a server.

Advantages:

  • Simple to set up
  • Low cost
  • No dedicated server required

Disadvantages:

  • Difficult to manage as the network grows
  • Security can be weaker
  • Backup is more difficult

4. Computer Network Architecture

Network architecture refers to the overall design of a network, including:

  • Network layers
  • Protocols
  • Services
  • Interfaces
  • Communication rules

The main purpose of network architecture is to divide the complex communication process into smaller, manageable layers.

Two important network architectures/models are:

  1. OSI Reference Model
  2. TCP/IP Model

5. Layered Architecture

Instead of designing networking as one large system, networking functions are divided into layers.

For example:

+-----------------------+
|   Application Layer   |
+-----------------------+
|   Transport Layer     |
+-----------------------+
|    Network Layer      |
+-----------------------+
|   Data Link Layer     |
+-----------------------+
|   Physical Layer      |
+-----------------------+

Each layer performs a specific function and communicates with the layer above and below it.

Why use layers?

Layering provides several benefits:

  1. Reduces complexity
  2. Makes network design easier
  3. Allows independent development of layers
  4. Makes troubleshooting easier
  5. Provides standard interfaces
  6. Allows protocols to be changed without redesigning the entire network

6. Protocols

A protocol is a set of rules that controls communication between devices.

For example, when two computers communicate, they need rules regarding:

  • Format of data
  • Addressing
  • Error handling
  • Data transmission
  • Timing
  • Flow control

Examples of network protocols:

  • HTTP
  • FTP
  • TCP
  • UDP
  • IP
  • DNS
  • Ethernet

7. Services and Protocols

A service tells us what a layer provides to the layer above it.

A protocol tells us how two corresponding layers communicate.

For example:

Computer A                     Computer B

Transport Layer  <---------->  Transport Layer
                     TCP

The two Transport Layers communicate using a transport protocol such as TCP.

The Transport Layer provides services to the Application Layer.

8. Connection-Oriented and Connectionless Architecture

Network communication can broadly be divided into two types.

Connection-Oriented Service

A connection is established before data transfer.

Connection Establishment
          ↓
      Data Transfer
          ↓
 Connection Release

Example: TCP

It provides reliable and ordered delivery of data.

Connectionless Service

No connection is established before sending each packet.

Data → Packet → Network

Each packet is treated independently.

Example: IP and UDP-based communication.

It is generally faster but may not provide reliable delivery by itself.

9. Network Architecture Example

Consider opening a website.

User
  ↓
Application Layer
  ↓
Transport Layer
  ↓
Network Layer
  ↓
Data Link Layer
  ↓
Physical Layer
  ↓
Internet / Network
  ↓
Destination Server

At the sender, data moves down through the layers.

At the receiver, data moves up through the layers.

This process is called encapsulation and decapsulation.

10. Encapsulation

When data moves down through the network layers, each layer may add its own control information.

Application Data
       ↓
Transport Header + Data
       ↓
Network Header + Transport Segment
       ↓
Data Link Header + Packet + Trailer
       ↓
Bits

At the receiving computer, the headers are removed layer by layer.

This is called decapsulation.

11. Structure vs Architecture

Network StructureNetwork Architecture
Describes network componentsDescribes overall communication design
Focuses on devices and connectionsFocuses on layers, protocols and services
Includes hosts, switches, routers, linksIncludes OSI, TCP/IP and protocols
More concerned with organizationMore concerned with communication rules
Can describe physical arrangementDescribes logical organization

Conclusion

Computer Network Structure describes the components of a network, such as hosts, communication links, switches, routers and servers, and how they are connected.

Computer Network Architecture describes the logical organization of communication using layers, protocols and services. Layered architectures such as the OSI and TCP/IP models make computer networks easier to design, understand, implement and troubleshoot.

⭐ Important MCA Exam Question

“Explain the structure and architecture of a computer network. Discuss layered architecture, protocols, services and client-server/peer-to-peer structures with suitable diagrams.”

This can easily be prepared as a 10-mark answer.