Computer networks are core computer science fundamentals, often covered in undergraduate courses. Understanding how these networks work is essential. Before diving into their workings, it’s important to grasp the basics of networks and the Internet.
Understanding Networks
- Network: A network is a group or system of interconnected people or Items. Examples include railway networks and social media networks.
- Computer Networks: A computer network is a group of computers connected with cables or wirelessly.
Why do we need Computer Networks?
- We need computer networks to share the Resources. For Example, Apple’s Airdrop allows files to be shared easily between devices.
The Internet
- Internet: In a nutshell, the Internet is a network of Computer Networks. It is a complex web of interconnected computer networks
- Example: Wi-Fi is a common way to connect to the internet.
History of Internet
- 1957: The Soviet Union launched the first satellite, Sputnik. In response, the United States of America created the Advanced Research Project and Agency (ARPA).
- 1960s – 1970s: ARPA developed a communication system for their computers, leading to the creation of ARPANET in 1969, which connected multiple computers.
- 1980s: The development of Transmission Control Protocol(TCP)/Internet Protocol(IP)laid the foundation for the modern Internet. These protocols allowed different networks to communicate, forming the basis of today’s internet.
- 1990s: The European Organization for Nuclear Researchers (CERN) utilized similar technologies for information sharing. Tim Berners-Lee, a researcher at CERN, introduced the World Wide Web (WWW), a system for storing and retrieving documents using hyperlinks. This innovation transformed how information was accessed and shared, leading to the development of early web browsers like Mosaic and Netscape Navigator.
Protocols
Traveling to a country involves following a set of rules, The same principle applies to the internet. For everyone to share information effectively, certain rules and steps must be followed. These rules are known as protocols.
Network Protocols are a set of Rules & Regulations set up to Communicate and share information over a network Ex:- HTTP, UDP, TCP, etc.
SMTP (Simple Mail Transfer Protocol)
If you want to send an email, the protocol is SMTP (Simple Mail Transfer Protocol).
Packets
When communicating between two computer systems the data cannot be sent in large chunks over the network. Every Network has a capacity limit, so data is divided into smaller chunks called packets.
Advantages of Packets:
- More Manageable
- Reusable
- Faster
- Leverage whole capacity
Address
Sending a parcel requires an address; sending messages over the Internet needs destination details.
Sending. Messages Requines over the Internet requin The destination details: This detail uniquely Identifies the end systems called Address. In the modern internet, we have IP Address.
Ports
Send a gift to a friend involves specifying the recipient by name. Any Machine can run multiple network applications, and ports are used to distinguish these applications for receiving messages.
when sending a message, an IP Address. IP addresses are used to identify the machine. Once the message reaches the machine, a port number is used to direct it to the correct application. The combination of an IP address and port number is called a socket(web sockets)
Summary of Ports:
- Ports help identify specific processes on a host.
- Every process has a 16-bit port number from 0-65535.
- Ports are categorized into three ranges:
- 0-1023 well-known ports – Reserved for specific applications (e.g., HTTP – port 80, HTTPS – port 443).
- 1024-49152 Registered ports – Used by specific, potentially proprietary applications or processes known but not system-defined.(e.g., SQL Server – port 1433, Mongo DB – port 27017).
- 49157-65835: Dynamic ports – Used for future purposes; users can utilize these ports for their services.
Access Networks
Access networks are the media through which end systems end systems connect to the internet. These networks and devices facilitate the connection to the internet.
- Network Interface Adapter (Hardware device):
- It enables a computer to attach to a network. There are different types of network interface adapters, that act as a bridge to connect to any network.
- Example: Wi-Fi adapter.
2. Digital Subscriber line (OSL):-
- DSL uses the existing telephone lines for internet connection.
- It is generally provided by the same company which supplies telephone services.
3. Intenet Service Provider(ISP):
An ISP is a company that provides end users with internet access.
Example: AT&T (Hardware part).
4. Other Access Networks:
- Cable Networks, Fibre Networks, Satelite Networks, and Starlinks
Protocol Stack
The Internet is a network of networks, while an Intranet is a private Internet. For example, ISRO has its own Intranet inaccessible from the internet, and vice versa.
There are two major models of standards:
Open Systems Interconnection (OSI) model (7 layers):
- Application Layer
- Presentation Layer
- Session layer
- Transport layer
- Network layer
- Data Link Layer
- Physical Layer.
Transmission Control Protocol / Internet protocol TCP/IP (5 layers):
- Application Layer (combines Application, Presentation, And Session layers from OSI)
- Transport layer
- Network layer
- Data link layer
- Physical layer
