Internet and Public Networks: Architecture, Working, Components & Examples
0Sahil Dubey
COMPUTER NETWORKS • CHAPTER 37
Internet and Public Networks: Architecture, Working, Components & Examples
We use the Internet every day, but the Internet is not one giant computer and it is not owned by one single company.
It is actually a huge network of networks where millions of smaller networks connect through routers, Internet Service Providers, backbone links, exchange points and common TCP/IP protocols.
When you open a website, your data may pass through your Wi-Fi router, local ISP, several Internet routers and possibly a CDN or data centre before reaching the final server.
EdgePhones, laptops, servers
Access NetworkWi-Fi, fibre, mobile
Internet CoreRouters & backbone
ServicesDNS, CDN, data centres
Direct Answer
The Internet is a worldwide system of interconnected computer networks that communicate mainly using the TCP/IP protocol suite.
Its architecture includes end devices, access networks, routers, Internet Service Providers, Autonomous Systems, Internet Exchange Points, backbone networks, DNS servers, data centres and content delivery infrastructure.
A public network is a network or communication service made available to a broad set of users, such as the public Internet or public telecommunications infrastructure.
What Is the Internet?
The Internet is a worldwide collection of interconnected computer networks.
These networks communicate using standard protocols, especially the TCP/IP protocol suite.
Simple Definition:
The Internet is a global network of networks that allows devices and computer networks around the world to communicate with each other.
The Internet connects:
Home networks
University networks
Office networks
Mobile networks
Cloud data centres
Government networks
Internet Service Providers
Content providers
Why Is the Internet Called a Network of Networks?
The Internet is not one single LAN or WAN.
Thousands of independently managed networks connect together.
Internet = Many Networks Connected Together
Home Network
Phones, laptop, smart TV
University Network
Labs, servers, Wi-Fi
INTERNET
INTERCONNECTION
Cloud Network
Servers and services
Mobile Network
Smartphones and telecom infrastructure
Company Network
Offices and enterprise systems
Remember:
Internet = Interconnected Networks
Internet vs World Wide Web
Students often use Internet and Web as if they mean the same thing.
They are related, but they are not identical.
Point
Internet
World Wide Web
Meaning
Global network infrastructure
System of web resources accessed over the Internet
Main Role
Provides connectivity
Provides linked web content
Protocols
IP, TCP, UDP and many others
Mostly HTTP and HTTPS
Example
Network connection itself
Websites viewed in a browser
Easy Difference:
Internet = Road system.
Web = One major service travelling on those roads.
Internet Architecture
The Internet can be understood using four simple parts:
1. Network Edge
End devices such as laptops, phones and servers.
2. Access Network
Connects end devices to the first network router.
3. Internet Core
High-speed routers and interconnected networks.
4. Service Infrastructure
DNS, CDN, cloud and data centres.
User Device
Laptop / Phone
Access Network
Wi-Fi / Fibre / Mobile
Internet Core
Routers + ISPs
Server
Website / Cloud
Network Edge
The network edge contains end systems that run applications.
Examples include:
Desktop computers
Laptops
Smartphones
Web servers
Email servers
IoT devices
Cloud servers
Edge = Where users and applications live.
Access Networks
An access network connects an end device to the first router or service-provider network.
Wi-Fi
Wireless access inside homes, offices and campuses.
Fibre Broadband
High-speed fixed Internet access.
Mobile Network
Internet through cellular systems.
Ethernet
Wired LAN access.
DSL
Broadband access over telephone-line infrastructure.
Cable Broadband
Internet over cable-network infrastructure.
Internet Core
The Internet core consists mainly of high-capacity routers and links that move packets between networks.
Routers examine destination information and forward packets toward the next hop.
The Internet core does not normally know the complete application meaning of every packet.
Its main job is to move packets toward their destinations.
Main Components of the Internet
End Devices
Phones, computers, servers and IoT devices.
An Internet Service Provider, or ISP, provides Internet connectivity to users or other networks.
ISP:
A company or organization that connects customers or networks to the Internet.
ISPs may serve:
Home users
Businesses
Universities
Data centres
Smaller ISPs
ISP Hierarchy
Internet connectivity is often explained using a simplified ISP hierarchy.
Global / Tier-1 Style Networks
Large backbone networks with extensive interconnection.
Regional / Tier-2 Style Networks
Connect regions and purchase or exchange connectivity.
Local Access ISP
Connects homes, offices and local customers.
End Users
Home, mobile, school or business customers.
The real Internet is not a perfect three-level tree.
Modern networks connect through many peering agreements, transit providers and exchange points.
Autonomous System
The Internet is divided into independently managed routing domains called Autonomous Systems.
Autonomous System:
A group of IP networks and routers operated under a common administrative routing policy.
AS
Independently managed routing domain.
Internal Routing
Routers exchange routes inside the AS.
External Routing
The AS exchanges routing information with other networks.
ASN
Autonomous Systems are identified using Autonomous System Numbers.
AS = One administrative routing domain.
Internet Exchange Point
An Internet Exchange Point, or IXP, is infrastructure where multiple independent networks can exchange traffic.
IXP:
A place where different networks connect and exchange Internet traffic directly.
IXPs can:
Reduce unnecessary long-distance traffic.
Improve latency.
Reduce dependence on upstream transit.
Make local traffic exchange more efficient.
Peering and Transit
Peering
Two networks exchange traffic directly according to an agreement.
Transit
One network pays another network to carry traffic toward the wider Internet.
IXP
Shared interconnection location that helps many networks peer efficiently.
Peering:
Networks exchange traffic.
Transit:
A provider carries traffic toward other parts of the Internet.
Internet Backbone
The term Internet backbone refers to high-capacity network infrastructure that carries large amounts of traffic between major networks and regions.
Backbone infrastructure commonly uses:
High-capacity fibre links
Core routers
Long-distance terrestrial connections
Submarine fibre-optic cables
Large interconnection facilities
The Internet backbone is not one single cable. It is a collection of interconnected high-capacity networks.
How Does the Internet Work?
Suppose you open:
https://example.com
A simplified sequence is:
Your device joins a local network.
DNS finds the IP address of the requested service.
Your device creates network packets.
Your router sends the packets toward the ISP.
Routers forward the packets across interconnected networks.
The packets reach the destination service or nearby CDN node.
The server processes the request.
Response packets travel back toward your device.
Complete Packet Journey
Packet Passport: Browser to Server
01
Application
Browser creates an HTTP or HTTPS request.
02
Transport Layer
TCP or another transport mechanism handles end-to-end transport.
03
Internet Layer
IP adds source and destination addressing.
04
Local Network
Frame carries the packet toward the local router.
05
ISP
Packet enters the service provider network.
06
Internet Routers
Routers choose the next hop toward the destination network.
07
Destination Network
Packet reaches the server or service infrastructure.
08
Response
Server sends data back through the Internet.
Packet Journey Trick:
Device → Router → ISP → Internet Core → Destination Network → Server
Routing and Forwarding on the Internet
Routing and forwarding are related but different.
Concept
Meaning
Routing
Learning or calculating paths through networks.
Forwarding
Sending an arriving packet to the correct outgoing interface or next hop.
Host A
Router 1
Router 2
Router 3
Server B
Routing:
Find the path.
Forwarding:
Move the packet to the next hop.
Role of DNS in the Internet
Users usually remember domain names instead of IP addresses.
DNS helps convert names into IP addresses.
User
Enters example.com
DNS Resolver
Searches for address
DNS System
Finds authoritative information
IP Address
Returned to client
DNS = Name to IP
Role of CDN in the Internet
CDN stands for:
Content Delivery Network
A CDN places copies or cached versions of content at distributed locations.
Instead of every user downloading content from one distant origin server, a nearby CDN node may serve it.
User
Requests content
Nearby CDN
Checks cache
Origin Server
Provides content if required
User Receives
Content from efficient location
CDN:
Bring content closer to users.
Data Centres
A data centre is a facility containing computing, storage and networking infrastructure.
Internet services may run across large data centres containing:
Servers
Storage systems
Network switches
Routers
Load balancers
Power systems
Cooling systems
Cloud services are physically backed by real computing and networking infrastructure inside data centres.
Role of TCP/IP in the Internet
The Internet mainly depends on the TCP/IP protocol suite.
Application Layer
HTTP, DNS, SMTP and application services
Transport Layer
TCP, UDP and other transport mechanisms
Internet Layer
IP and routing-related functions
Network Access
Ethernet, Wi-Fi and physical transmission
TCP/IP makes different networks communicate using common rules.
Important Internet Protocols
HTTP / HTTPS
Web communication.
DNS
Domain name resolution.
TCP / UDP
Transport services.
IP
Packet addressing and delivery across networks.
SMTP
Email transfer.
FTP
File transfer.
DHCP
Automatic IP configuration.
ICMP
Network control and diagnostic messages.
BGP
Inter-domain routing between Autonomous Systems.
TLS
Cryptographic protection for many application communications.
What Is a Public Network?
A public network is a communication network or service that is available to a broad population rather than being restricted to one private organization.
Public Internet
Global interconnected network accessible through Internet service providers.
Public Mobile Network
Cellular service used by many subscribers.
Public Telecommunications Network
Communication infrastructure offered to the public by service providers.
A “public network” does not mean every device or every piece of data on it is publicly accessible.
Security controls can still protect individual systems and services.
Public Network vs Private Network
Public Network
Available to a broad set of users through a public service or provider.
Private Network
Restricted to specific users, devices or an organization.
Intranet
Private internal network that may use Internet technologies such as TCP/IP and web applications.
Point
Public Network
Private Network
Access
Broad user population
Restricted users
Control
Shared across providers and networks
Usually controlled by one organization or owner
Example
Public Internet
Office LAN
Security
Must assume communication may cross untrusted infrastructure
Access may be more controlled, but security is still required
Public IP Address vs Private IP Address
Public IP Address
Globally routable address used on the public Internet.
Private IP Address
Address used inside private IPv4 networks.
NAT
Can translate private internal addresses when traffic accesses external networks.
Common private IPv4 ranges include:
10.0.0.0/8 172.16.0.0/12 192.168.0.0/16
NAT and Internet Access
NAT stands for:
Network Address Translation
Many home networks use private IP addresses internally.
The router performs address translation when devices communicate with the public Internet.
Inside:
Private IP
Router:
NAT
Outside:
Public Internet communication
Important Internet Design Issues
Scalability
The Internet must support enormous numbers of devices and networks.
Routing
Networks must exchange and maintain route information efficiently.
Addressing
Devices and interfaces need meaningful network addresses.
Reliability
Traffic should continue when possible even if some links fail.
Security
Public infrastructure exposes communication to many threats.
Congestion
Too much traffic can reduce performance.
Latency
Long geographic paths and processing add delay.
Interoperability
Different networks must communicate using common standards.
Availability
Services should remain reachable despite failures.
Reliability and Redundancy
The Internet is designed with many alternate paths and independently operated networks.
If one link fails, routing systems may sometimes find another available path.
Redundancy means keeping alternate links, routers or systems so that one failure does not always stop the complete service.
Redundancy improves availability, but it does not guarantee that every failure will be invisible to users.
Internet Scalability
The Internet must support very large numbers of:
Users
Devices
Networks
Routes
Websites
Cloud services
Scalability is supported through ideas such as:
Hierarchical addressing
Distributed DNS
Autonomous Systems
Routing aggregation
Content Delivery Networks
Distributed data centres
Internet Security
The Internet is a public and highly interconnected environment, so security is extremely important.
Common protections include:
TLS / HTTPS
Firewalls
Authentication
Encryption
VPNs
Digital certificates
Access controls
Secure DNS technologies in some deployments
Connecting to the Internet does not automatically make a system secure.
Security must be designed at several layers.
Real-Life Internet Working Examples
Example 1 - Opening a Website
1
User enters a domain name.
2
DNS resolves the name.
3
Packets move through router and ISP.
4
Internet routers forward traffic toward the server.
5
Server or CDN sends web content back.
Example 2 - Watching an Online Video
1
Video application requests content.
2
DNS may direct the user toward an efficient service location.
3
A CDN may serve video from a nearby node.
4
Packets continuously travel through the Internet to the user.
Example 3 - Sending Email
1
Mail application submits the message.
2
Mail servers exchange traffic through the Internet.
3
Receiver later accesses the stored email.
Solved Internet Examples and Numericals
Numerical 1: Transmission Time
A 100 MB file is sent over a 50 Mbps connection.
File Size = 100 MB
= 100 × 8
= 800 Mb
Transmission Time = Data Size / Data Rate
Time = 800 / 50
= 16 seconds
Answer = 16 seconds
Ignoring protocol overhead, congestion and other delays.
Numerical 2: Router Hop Count
A packet passes through:
Router A → Router B → Router C → Router D
Number of routers crossed:
4 router hops
Numerical 3: Round-Trip Delay
Suppose one-way propagation and network delay is approximately:
One-Way Delay = 40 ms
Assuming a symmetric path and ignoring processing differences:
RTT ≈ 2 × 40
= 80 ms
Approximate RTT = 80 ms
Numerical 4: Private Address Check
Address:
192.168.1.20
This belongs to:
Private IPv4 address space.
Numerical 5: Public Address Concept
A globally routable address assigned by an ISP is used to communicate on the public Internet.
This is a public IP address concept.
Numerical 6: Total Delay
Suppose:
Transmission Delay = 10 ms
Propagation Delay = 20 ms
Processing Delay = 2 ms
Queuing Delay = 8 ms
Total Delay = Transmission + Propagation + Processing + Queuing
Total = 10 + 20 + 2 + 8
= 40 ms
Answer = 40 ms
Internet and Public Networks Remember Tricks
Internet:
Network of networks.
Edge:
Users and servers.
Access Network:
Connects user to ISP.
Core:
Routers and high-speed links.
ISP:
Internet connectivity provider.
AS:
One administrative routing domain.
IXP:
Networks meet and exchange traffic.
Peering:
Networks directly exchange traffic.
Transit:
Provider carries traffic to wider Internet.
DNS:
Name to IP.
CDN:
Content closer to user.
Routing:
Find path.
Forwarding:
Send to next hop.
NAT:
Translate network addresses.
Public Network:
Available to broad users.
Common Internet Exam Mistakes
1. Internet and World Wide Web are the same.
Wrong. The Web is one service that operates over the Internet.
2. The Internet is owned by one company.
Wrong. The Internet is made of many independently operated networks.
3. Internet backbone means one main cable.
Wrong. It means interconnected high-capacity infrastructure operated by multiple networks.
4. Router and ISP mean the same thing.
Wrong. A router is a network device. An ISP is a service provider or network operator.
5. DNS carries every web page.
Wrong. DNS mainly resolves names and provides DNS records. HTTP or HTTPS carries web application data.
6. CDN and DNS are the same.
Wrong. DNS resolves names, while a CDN distributes content.
7. Public network means no security is possible.
Wrong. Public networks can use encryption, authentication and other security controls.
8. Private IP addresses are globally routable on the public Internet.
Wrong. Private IPv4 addresses are intended for private networks.
9. Routing and forwarding are identical.
Wrong. Routing finds or learns paths; forwarding moves individual packets to the next hop.
10. The Internet core contains only servers.
Wrong. The core mainly contains high-capacity routers and network links.
11. IXP means Internet Exchange Protocol.
Wrong. IXP means Internet Exchange Point.
12. An Autonomous System means one router.
Wrong. An AS can contain many routers and IP networks under one routing administration.
13. NAT itself is the Internet.
Wrong. NAT is an address-translation mechanism often used at network boundaries.
14. Every Internet path is fixed forever.
Wrong. Routing paths can change because of policy, failures and network conditions.
40 Important Internet and Public Network Questions With Answers
1. What is the Internet?
Answer: The Internet is a worldwide system of interconnected networks that communicate using common protocols, mainly the TCP/IP protocol suite.
2. Why is the Internet called a network of networks?
Answer: Because it connects many independently managed local, regional, enterprise, mobile and service-provider networks.
3. Is the Internet the same as the World Wide Web?
Answer: No. The Internet is the communication infrastructure, while the Web is a service that uses the Internet.
4. What is the network edge?
Answer: The network edge contains end systems such as user devices and servers where applications run.
5. What is an access network?
Answer: An access network connects end devices to the first router or service-provider network.
6. Give examples of access networks.
Answer: Wi-Fi, Ethernet, fibre broadband, DSL, cable broadband and mobile networks.
7. What is the Internet core?
Answer: The Internet core is the interconnected system of routers and high-capacity links that carries packets between networks.
8. What is an ISP?
Answer: ISP means Internet Service Provider and provides Internet connectivity to users or other networks.
9. What is an Autonomous System?
Answer: An Autonomous System is a collection of IP networks and routers operated under a common administrative routing policy.
10. What is an ASN?
Answer: ASN means Autonomous System Number and identifies an Autonomous System for inter-domain routing purposes.
11. What is an IXP?
Answer: IXP means Internet Exchange Point, where independent networks interconnect and exchange Internet traffic.
12. What is peering?
Answer: Peering is an arrangement in which networks directly exchange traffic with each other.
13. What is Internet transit?
Answer: Transit is a service where one network pays another network to carry traffic toward destinations across the wider Internet.
14. What is the Internet backbone?
Answer: It is high-capacity interconnected network infrastructure that carries large volumes of Internet traffic between major networks and regions.
15. What does a router do on the Internet?
Answer: A router forwards packets between networks based on routing and forwarding information.
16. What is routing?
Answer: Routing is the process of learning or calculating paths through interconnected networks.
17. What is forwarding?
Answer: Forwarding means sending an arriving packet to the appropriate outgoing interface or next hop.
18. What is the role of DNS?
Answer: DNS resolves domain names to IP addresses and provides other domain-related information.
19. What is a CDN?
Answer: CDN means Content Delivery Network and distributes content across multiple locations so users can often receive it from a nearby or efficient node.
20. What is a data centre?
Answer: A data centre is a facility containing servers, storage and networking systems used to host applications and services.
21. Which protocol suite is mainly used by the Internet?
Answer: TCP/IP.
22. What does IP do?
Answer: IP provides addressing and packet delivery across interconnected networks.
23. What is a public network?
Answer: A public network is a network or communication service available to a broad population of users.
24. Give one example of a public network.
Answer: The public Internet.
25. What is a private network?
Answer: A private network is restricted to authorized users or devices, usually under one organization or owner.
26. What is an intranet?
Answer: An intranet is a private organizational network that often uses Internet technologies such as TCP/IP and web applications.
27. What is a public IP address?
Answer: A public IP address is globally routable on the public Internet.
28. What is a private IP address?
Answer: A private IPv4 address is used inside private networks and is not directly routed on the public Internet.
29. What is NAT?
Answer: NAT is Network Address Translation and changes address information when traffic passes between different address domains.
30. Why is NAT commonly used in home networks?
Answer: It allows multiple private-address devices to access external networks through translated address information.
31. What is Internet scalability?
Answer: Scalability is the ability of Internet architecture to support growth in users, devices, networks, routes and services.
32. How do CDNs improve Internet performance?
Answer: They place content at distributed locations so requests can often be served from a closer or more efficient location.
33. How does redundancy help the Internet?
Answer: Alternate links and systems can allow traffic or services to continue when some components fail.
34. What is Internet latency?
Answer: Internet latency is the delay experienced while data travels through network links, devices and processing systems.
35. What causes Internet delay?
Answer: Transmission, propagation, processing and queuing delays all contribute to total network delay.
36. Why does the Internet require security?
Answer: Because traffic may pass through public or untrusted infrastructure and can face threats such as interception, spoofing and modification.
37. A 100 MB file is transferred at 50 Mbps. Find ideal transmission time.
38. A one-way delay is 40 ms. What is approximate RTT if both directions are equal?
Answer: Approximately 80 ms.
39. Is 192.168.1.25 a public or private IPv4 address?
Answer: It is a private IPv4 address.
40. Give the easiest Internet memory line.
Answer: Internet is a network of networks where devices connect through access networks and ISPs, routers move packets across the core, and services such as DNS and CDN help users reach content efficiently.
20 Internet and Public Network MCQs With Answers
1. The Internet is best described as:
A. One LAN
B. Network of networks
C. One server
D. One router
Answer: B
2. Which protocol suite is mainly used by the Internet?
A. TCP/IP
B. Bluetooth only
C. Token Ring only
D. FDDI only
Answer: A
3. A device that forwards packets between networks is:
A. Router
B. Keyboard
C. Monitor
D. Printer
Answer: A
4. ISP stands for:
A. Internet Service Provider
B. Internal System Protocol
C. Internet Security Packet
D. Integrated Switching Port
Answer: A
5. DNS is mainly used for:
A. Name resolution
B. File compression
C. Routing hardware
D. Display resolution
Answer: A
6. CDN stands for:
A. Content Delivery Network
B. Central Data Node
C. Computer Domain Network
D. Content Domain Number
Answer: A
7. IXP stands for:
A. Internet Exchange Point
B. Internet External Protocol
C. Internal Exchange Port
D. IP Extension Process
Answer: A
8. An Autonomous System is:
A. One administrative routing domain
B. One computer only
C. One Ethernet frame
D. One web page
Answer: A
9. Peering means:
A. Networks directly exchange traffic
B. Deleting IP addresses
C. Compressing packets
D. Replacing routers
Answer: A
10. Transit means:
A. Provider carries traffic toward wider Internet
B. Browser caches an image
C. DNS deletes a domain
D. Router becomes a switch
Answer: A
11. Which is part of the network edge?
A. Laptop
B. Submarine cable only
C. Core router only
D. IXP only
Answer: A
12. Which connects users to the first provider router?
A. Access network
B. Hash function
C. Presentation Layer
D. Digital signature
Answer: A
13. Public Internet is an example of:
A. Public network
B. Private-only LAN
C. Local loop only
D. Offline network
Answer: A
14. Which is a private IPv4 range?
A. 192.168.0.0/16
B. Any random public block
C. All IPv4 addresses
D. None
Answer: A
15. NAT stands for:
A. Network Address Translation
B. Network Access Terminal
C. Node Address Table
D. Network Application Transfer
Answer: A
16. Routing means:
A. Finding network paths
B. Displaying images
C. Writing HTML only
D. Compressing files
Answer: A
17. Forwarding means:
A. Sending packet to next hop
B. Finding all passwords
C. Encrypting hard disk
D. Creating DNS names
Answer: A
18. Which improves content delivery by distributing copies of content?
A. CDN
B. ARP only
C. MAC table only
D. BIOS
Answer: A
19. The World Wide Web is:
A. A service that uses the Internet
B. Exactly the same as all Internet infrastructure
C. One router
D. One DNS server
Answer: A
20. Best memory line for Internet is:
A. Network of networks
B. One global computer
C. One website
D. One LAN
Answer: A
Frequently Asked Questions
What is the Internet in simple words?
The Internet is a global network of interconnected computer networks that communicate using common protocols.
Why is the Internet called a network of networks?
Because many independent networks such as home, university, mobile, business and ISP networks are interconnected.
What is the Internet core?
The Internet core consists mainly of high-capacity routers and links that move packets between networks.
What is an ISP?
An ISP is an Internet Service Provider that provides Internet connectivity to customers or other networks.
What is an Autonomous System?
An Autonomous System is a group of IP networks and routers under one administrative routing policy.
What is an IXP?
An Internet Exchange Point is infrastructure where independent networks connect and exchange traffic directly.
What is peering?
Peering is an arrangement in which two networks exchange traffic directly according to an interconnection agreement.
What is a CDN?
A Content Delivery Network distributes content across multiple locations so that users can often receive it from a nearby or efficient server.
What is a public network?
A public network is a communication network or service made available to a broad user population.
What is the difference between public and private IP addresses?
Public IP addresses are globally routable on the Internet, while private IPv4 addresses are used inside private networks and are not directly routed on the public Internet.
What is NAT?
NAT means Network Address Translation and changes address information when traffic crosses network boundaries.
What is the difference between Internet and Web?
The Internet is the global network infrastructure, while the World Wide Web is one service that uses this infrastructure.
