1Computer network System
A computer network system is defined as the interconnection of two or more computers. It is done to enable computers to communicate and share available resources.
2Applications of a computer network system
- Sharing of resources, such as printers.
- Sharing of expensive software and database.
- Communication from one computer to another computer.
- Exchange of data and information among users via a network.
- Sharing of information over geographically wide areas.
3Types of a computer network system
Some major types of computer networks are as follows.
- Local area network
- Metropolitan area network
- Wide area network
- Personal area network
- Personal area network
Local area network
- A local area network (LAN) is designed for small physical areas such as an office, a group of buildings, or a factory.
- LANs are used widely as they are easy to design and troubleshoot. Personal computers and workstations are connected through LANs.
- We can use different types of topologies through LAN, including Star, Ring, Bus, Tree, etc.
- A LAN can be a simple network such as connecting two computers, sharing files and
networks among each other, while it can also be as complex as interconnecting an entire building LANs are also widely used to share resources such as printers, shared hard drives, etc.
Metropolitan area network
- A metropolitan area network (MAN) is a bigger version of LAN. It uses similar technology as LAN.
- It covers a large geographical area and may serve as an ISP (Internet service provider). A MAN is designed for customers who need high-speed connectivity.
- The data transfer rate and the propagation delay of MAN are moderate.
- Devices used for transmission of data through MAN are: modem and wire/cable Examples of a MAN is the part of the telephone company network that can provide a high-speed DSL line to the customer or the cable TV network in a city.
Wide area network
- A wide area network (WAN) is a computer network that extends over a large geographical area, although it might be confined within the bounds of a state or country.
- A WAN could be a connection of LAN connecting to other LANs via telephone lines and radio waves and may be limited to an enterprise (a corporation or an organization) or accessible to the public.
- The technology is a high speed and relatively expensive. Devices used for transmission of data through WAN are optic wires, microwaves, and satellites.
- There are two types of WAN: switched WAN and point-to-point WAN. An example of a switched WAN is the asynchronous transfer mode (ATM) network, and an example of a point-to-point WAN is a dial-up line that connects a home computer to the Internet.
Personal area network
- A personal area network (PAN) is the smallest type of network, which is made up of a wireless modem, a computer or two, phones, printers, tablets, etc., and revolves around one person in one building.
- These types of networks are typically found in small offices or residences and are managed by one person or organization from a single device.
Virtual private network
- A virtual private network (VPN) is a technology that creates a safe and encrypted connection over a less secure network, such as Internet VPN technology was developed as a way to allow remote users and branch offices to securely access corporate applications and other resources.
- To ensure safety, data travels through secure tunnels, and VPN users must use authentication methods including passwords, tokens, and other unique identification methods to gain access to the VPN.
- An Internet connection is a service that provides access to the global system of interconnected computer networks.
- The speed of the Internet connection depends on the bandwidth.
5Types of Internet connections
Some major types of Internet connections are described as follows.
- Dial-up Connection
- Broadband Connection
- Wireless Connection
- A dial-up connection technology dials into the network through an existing phone line, creating a semi-permanent link to the Internet.
- Operating on a single channel, it monopolizes the phone line and is the slowest method of accessing the Internet.
- It is often the only form of Internet access available in rural areas, as it requires no infrastructure, other than the already existing telephone network, to connect to the Internet.
- Usually, dial-up connections do not exceed a speed of 56 kbit/s, as they are primarily made via a 56k modem.
- The term broadband connection includes a broad range of technologies, all of which provide high data rate access to the Internet.
- It provides a continuous connection; there is no dial-up/in-process required and it does not “hog” phone lines.
- It truly is the most used form of Internet access because of its high access speeds.
A broadband connection is offered in different forms as follows:
Digital subscriber line
Digital subscriber line (DSL):
- This uses an existing two-wire copper telephone line connected to the premise, so service is delivered simultaneously with wired telephone service, it will not tie up your phone line as an analog dial-up connection does.
- The two main categories of DSL for home subscribers are called ADSL and SDSL.
- All types of DSL technologies are collectively referred to as xDSL. An xDSL connection’s speed ranges from 128 Kbps to 9 Mbps.
- This transmits data via airwaves on the cable television infrastructure.
- It is provided by the local cable TV provider through a cable modem. Data is transmitted via a coaxial cable or a hybrid fiber-coaxial cable.
- Cable speeds range from 512 Kbps to 20 Mbps.
- This transfers data fully or partially via fiber optic cables. “Fiber” refers to the thin glass wires inside the larger protective cable.
- “Optic” refers to the way the type of data transferred light signals.
- Fiber connections can provide homes and businesses with data transfer speeds of 1 Gbps.
- Optical fiber cables can be used as an earthquake detection systems too.
Broadband over power line (BPL):
- This technology makes possible high-speed Internet and home network access over ordinary residential electrical lines and power cables.
- It was created as an alternative to other wired broadband Internet systems such as the DSL and cable modem.
- Some people use the term BPL to refer specifically to the home networking aspects of power line communications and IPL (Internet over power line) to refer to long-distance Internet usages.
- ln a wireless type of Internet connection, radio frequency bands are used in place of telephone or cable networks.
- This Internet connection is the “always-on” connection that can be accessed from any location that falls within the network coverage.
- Wireless connections are made possible through the use of a modem, which picks up Internet signals and sends them to other devices.
Some ways to connect the Internet wirelessly are as follows:
Wireless fidelity (Wi-Fi):
- Wi-Fi uses radio waves to provide wireless high-speed Internet and network connections.
- Wireless (or Wi-Fi) hotspots are essentially wireless access points providing network and/or Internet access to mobile devices such as your laptop or smartphone, typically in public locations, such as shopping malls, restaurants, hotels, airports, railway station, parks, etc.
Worldwide Interoperability for Microwave Access (WiMAX):
- This is a standardized wireless version of Ethernet intended primarily as an alternative to wire technologies (such as cable modems, DSL) to provide broadband access to customer premises.
- It would operate similar to Wi-Fi but at higher speeds over greater distances and for a greater number of users.
Mobile wireless broadband service:
- This is also called as mobile broadband.
- It also referred to as WWAN (for wireless wide area network) and is a general term used to describe high-speed Internet access from mobile providers for portable devices.
- Mobile broadband services can also provide wireless Internet access on your laptop or netbook using built-in mobile broadband network cards or other portable network devices, such as USB modems or portable Wi-Fi mobile hotspots.
Internet over satellite (loS):
- loS allows a user to access the Internet via a satellite that orbits the earth.
- A satellite is placed at a static point above the earth’s surface, in a fixed position.
- The enormous distance that a signal travels from the earth to the satellite and back again provides a delayed connection compared to cable and DSL.
6Network Architecture in Computer Network System
Network Architecture can be broadly classified as using either Peer-to-peer network/Client/Server network architecture.
- A peer-to-peer network is also known as a P2P network. In this, each workstation has equivalent capabilities and responsibilities.
- This differs from the client/server architecture in which some workstations are dedicated to serving others.
- Peer-to-peer networks are generally simpler and less expensive, but they
usually do not offer the same performance under heavy loads.
Client/Server network in Computer Network System
- In a client/server architecture, each computer or process on the network is either a client or a server.
- Servers are powerful computers or processors dedicated to managing disk drives (file servers), printers (print servers), or network traffic (network servers).
- Clients are less powerful PC workstations on which users run applications.
- Clients rely on servers for resources, such as files, devices, and even processing power.
70SI model in Computer network system
- Some so many users use a computer network and are located in the world.
- So, the International organization of Standardization (ISO) has developed a standard to ensure, national, and worldwide data communication, systems must be developed that are compatible to communicate with each other.
- This is called a model for Open System Interconnection (OSI) and is commonly known as the OSI model.
This model has a seven-layer architecture. It defines seven layers or levels in a complete communication system.
- The application layer is the layer that the users and user applications most often interact with.
- Network communication is discussed in terms of availability of resources, partners to communicate with, and data synchronization.
The presentation layer is responsible for mapping resources and creating context. It is used to translate lower-level networking data into data that applications expect to see.
The session layer is a connection handler. It creates, maintains, and persistently destroys connections between nodes.
- The transport layer is responsible for handing the layers above it a reliable connection.
- In this context, reliable refers to the ability to verify that a piece of data was received
intact at the other end of the connection.
- This layer can resend information that has been dropped or corrupted and can
acknowledge the receipt of data to remote computers.
- The network layer is used to route data between different nodes on the network. It uses addresses to be able to identify which computer to send information to.
- This layer can also breakdown larger messages into smaller chunks to be reassembled on the opposite end.
This layer is implemented as a method of establishing and maintaining reliable links between different nodes or devices on a network using existing physical connections.
- The physical layer is responsible for handling the actual physical devices that are used to make a connection.
- This layer involves the bare software that manages physical connections as well as the hardware itself (like Ethernet).
8Network devices used in Computer network system
Network devices are components used to connect computers or other electronic devices so that they can share files or resources.
Different networking devices have different roles to play in a computer network. Some major computer networking devices are as follows.
- A repeater operates at the physical layer.
- Its job is to regenerate the signal over the same network before the signal becomes too weak or corrupted to extend the length to which the signal can be transmitted over the same network.
- An important point to be noted about repeaters is that they do no amplify the signal.
- When the signal becomes weak, they copy the signal bit-by-bit and regenerate it at the original strength.
- It is a two-port device.
- A hub is a multiport repeater.
- A hub connects multiple wires coming from different branches, for example, the connector in a star topology that connects different stations.
- Hubs cannot filter data, so data packets are sent to all connected devices.
- In other words, a collision domain of all hosts connected through a hub remains one.
- Also, they do not have the intelligence to find out the best path for data packets, which leads to inefficiencies and wastage.
- A bridge operates at the data link layer.
- A bridge is a repeater, with add on the functionality of filtering content by reading the MAC addresses of source and destination.
- lt is also used for interconnecting two LANS working on the same protocol.
- It has a single input and single output port, thus making it a two-port device.
- A gateway, as the name suggests, is a passage to connect two networks that may work upon different networking models.
- They work as the messenger agents that take data from one system, interpret it, and transfer it to another system.
- Gateways are also called protocol converters and can operate at any network layer.
- Gateways are generally more complex than a switch or router.
A switch is a multiport bridge with a buffer and a design that can boost its efficiency (a large number of ports imply less traffic) and performance.
- A Switch is a data link layer device.
- A switch can perform error checking before forwarding data that makes it very efficient as it does not forward packets that have errors and forward good packets selectively to the correct port only.
- In other words, a switch divides the collision domain of hosts, but the broadcast domain remains the same.
- A router is a device like a switch that routes data packets based on their IP addresses. A router is mainly a network layer device.
- Routers normally connect LANs and WANs and have a dynamically updating routing table based on which they make decisions on routing the data packets.
- Routers divide broadcast domains of hosts connected through it.
- The modem stands for a modulator-demodulator.
- That means it modulates and demodulates the signal between the digital data of a computer and the analog signal of a telephone line.
- It converts the computer-generated digital signals of a computer into analog signals to enable their traveling via phone lines.
- It can be used as a dial-up for a LAN or to connect to an ISP.
- It can be both external, as in the device that connects to the USB or the serial port of a computer, or proprietary devices for handheld gadgets and other devices, as well as internal; in the form of add-in expansion cards for computers and PC cards for laptops.
9Network host in Computer Network System
- A network host refers to any computer (or server) that is interlinked with another computer(s) or network devices through an Internet connection.
- Each host has its unique IP address, formed by the computer’s local number and the particular number of the network it belongs to.
- The network host is responsible for storing data that will be transmitted to other computable devices, usually user’s computers, called remote terminals.
10Network protocol in Computer Network System
- The rules and conventions for communication between network devices are defined as a network protocol.
- It includes the characteristics of a network, such as access method, allowed physical topologies, types of cabling, and speed of data transfer.
- Several types of computer network protocols have been developed for specific purposes and environments. Some major network protocols are described, including TCP, IP, POP, SMTP, HTTP, FTP, SSH, PPP, WAP, and VolP
Transmission control protocol
- The transmission control protocol (TCP) is a communication protocol that computers use to communicate over a network.
- It divides a message into a stream of packets that are sent and then reassembled at the destination.
- The Internet protocol (IP) is an addressing protocol.
- It is always used together with TCP. The IP addresses the packet, routes them through different nodes and networks until they reach their final destination.
- TCP/IP is perhaps the most used standard protocol for connecting computer networks.
Internet protocol address
- An Internet protocol (IP) address is the unique numerical address of a device in a computer network that uses the IP for communication.
- An IP address consists of four numbers; each can contain one to three digits. These numbers are separated with a single dot ().
- These four numbers can range from0 to 255. Some types of IP address are described next.
Public IP address
- A public IP address is used for the identification of a home network to the outside world.
- It is unique throughout the entire network. It is used on the Internet or other WAN.
- It is an IP address that your home or business router receives from your ISP.
- Public IP addresses are required for any publicly accessible network hardware, such as for your home router, as well as for the servers that host websites.
- It is sometimes called an Internet IP address.
Finding your public IP address
Go to Google and search for “ip”; it will show your public IP address:
Websites for finding IP addresses are:
Private IP address
- A private IP address is used for the identification of network devices inside the home network.
- Two or more separate networks can have the same private IP addresses assigned to different computers.
- It is used on a LAN for computers not directly connected to the Internet.
- It is an IP address that is reserved for internal use behind a router or other network address translation (NAT) device, apart from the public.
- It is also known as a local IP address.
Finding your private IP address for Computer Network System
For Windows OS users:
To open Command Prompt: Press the Windows key + R, then type cmd and click on OK:
In the command prompt window, type ipconfig and press Enter:
For Linux users:
Linux users can launch the Terminal window and enter the command hostname -1, ifconfig, or ip addr show.
Mac OS users can use the command ifconfig.
Dynamic IP address
- A dynamic IP address is an IP address that is automatically assigned to each connection of a network by a Dynamic Host Configuration Protocol (DHCP) server.
- It’s called dynamic because it constantly changes.
- It is good for residential users and small business owners.
- The public IP address that gets assigned to the router of most home and business users by their ISPs is a dynamic IP address.
- The upload and download speed of a dynamic IP address is slower than the static IP address.
Static IP address
- A static IP address is an IP address that was manually configured for a device.
- It’s called static because it doesn’t change.
- Routers, phones, tablets, desktops, laptops, and any other device that can use an IP address can be configured to have a static IP address.
- It is widely used by web servers, e-mail servers, and other Internet servers.
- Also, it is used for voice over IP (VOIP), VPN, playing online games, or game hosting.
- The upload and download speed of a static IP address is faster than a dynamic IP address.
Both private and public IP addresses are either dynamic or static, which means that, respectively, they either change or they don’t.
- The Post Office Protocol (POP) is used to receive incoming e-mails.
- The Simple Mail Transport Protocol (SMTP) is used for sending and distributing outgoing e-mails.
Hypertext Transfer Protocol in Computer Network System
- The Hypertext Transfer Protocol (HTTP) is used to transfer a hypertext between two or more computers. Generally, it is used by a webserver to allow web pages to be shown in a web browser.
- Hypertext is the text that is coded using the language called HTML. HTTP is based on the client/server principles, for example, https://www.google.co.in.
- Hypertext Markup Language (HTML) is a standardized system for tagging text files to achieve font, color, graphic, and hyperlink effects on World Wide Web pages.
- It defines the structure and layout of a web document by using a variety of tags and attributes.
- HyperText Transfer Protocol Secure (HTTPS) is the secure version of HTTP, the protocol over which data is sent between your browser and the website that you are connected to.
File Transfer Protocol
- The File Transfer Protocol (FTP) allows users to transfer files from one computer to another computer.
- Files that can be transferred may include program files, text files, and multimedia files, etc.
- This method of file transfer is faster than using HTTP. With a free FIP client software (such as FileZilla, Cyberduck or Transmit) uploading/downloading a file is really easy through the Internet.
- The SSH protocol is a method for secure remote login from one computer to another. It is also known as Secure Shell.
- It provides several alternative options for strong authentication, and it protects the communications security and integrity with strong encryption.
- It is a secure alternative to the non-protected login protocols (such as Telnet).
- It is also used for interactive and automated file transfers.
- The Point-to-point Protocol (PPP) provides a standard way to transport multiprotocol data over point-to-point links.
- It has three main components: a way to encapsulate multiprotocol datagrams; a Link Control Protocol to establish, configure, and test the data-link connection; and a group of network control protocols that establish and configure different types of network
Wireless Application Protocol
The Wireless Application Protocol (WAP) is a communications protocol that is used for wireless data access through most mobile wireless networks.
- VoIP is the transmission of voice over IP networks.
- It is also referred to as IP telephony, Internet telephony, and Internet calling.
- A Telnet program runs on your computer and connects your PC to a server on the network.
- This enables you to control the server and communicate with other servers on the network.
- To start a Telnet session, you must log in to a server by entering a valid username and password.
- It is a common way to remotely control web servers Usenet is a collection of user-submitted notes or messages on various subjects that are posted to servers on a
- Each subject collection of posted notes is known as a newsgroup.
- The Network News Transfer Protocol (NNTP) is the predominant protocol used by computer clients and servers for managing the notes posted on Usenet newsgroups.
- Gopher is a sort of rule used to search, retrieve, and display documents from remote sites.
- It is possible to initiate online connections with other systems through Gopher.
- It also operates on the client/server principle.
11What is the Network port in Computer Network System?
- A network port allows software applications to share hardware resources without interfering with each other.
- Port numbers are used to determine what protocol incoming traffic should be directed to.
- Each port number identifies a distinct service. The network ports are numbered from 0 to 65535. Port use is regulated by the Internet Corporation for Assigned Names and
12What is the Network packet in Computer Network System?
- A network packet is a basic unit of communication over a digital network.
- It is also called a datagram, a segment, a block, a cell, or a frame or an IP packet, depending on the protocol used for the transmission of data.
- The IP requires a packet to have three basic elements: source, destination, and data.
- Packets are transmitted over packet-switched networks, which are networks in which
each message (i.e., data that is transmitted), such as an e-mail, web page, or program download, is cut up into a set small segment prior to transmission.
- Each packet consists of three main parts: a header, a payload, and a footer.
- A header consists of instructions regarding its packet data.
- A payload is the actual data (i.e., part of the message) that the packet is delivering to the destination. It is also called a body or data area.
- A footer contains several bits that tell the receiving device that it has reached the end of the packet. It is also called as a trailer.
- It may also include some type of error checking.
13What is Ping in Computer Network System?
- Ping is a network utility used to send a test packet, or echo packet, to a machine to find out whether the machine is reachable and how long the packet takes to reach the machine.
- An example of the ping command executed in the Command Prompt is shown as follows:
- To open the Command Prompt, press the Windows key + R, then type cmd and click on OK.
In the command prompt window, type ping www.ratingsera.in and press Enter.
- The preceding screenshot shows you that an echo packet was sent to the destination and returned.
- The TTL (time to live) item shows how many intermediary steps, or hops, the packet should take to the destination before giving up.
- Tracert command not only tells you whether the packet got to its destination and how long it took but also tells you all the intermediate hops it took to get there. You can use the tracert command in Command Prompt.
- Open the Command Prompt, type tracert www.ratingsera.in, and press Enter.
- Netstat is another network utility command that shows you what connections your computer currently has.
- It is an abbreviation for network status. You can use it in the Command Prompt.
- A MAC (Media Access Control) address is a globally unique identifier assigned to network devices, and therefore, it is often referred to as hardware or physical address.
- The purpose of MAC addresses is to provide a unique hardware address or physical address for every node on a LAN or other network.
- A node is a point at which a computer or other device (eg, a printer or router) is connected to the network. A MAC address is 48 bits in length.
How to find your MAC address
To open the Command Prompt: press the Windows key + R, then type cmd and click on OK.
In the Command Prompt window, type ipconfig/all and press Enter.
You can see your MAC address in the Physical Address field, as seen in the preceding screenshot.
15Domain Name System
- A Domain Name System (DNS) is used to translate hostname or Internet domain into IP addresses and vice versa.
- When you visit www.google.com in a browser, your computer uses DNS to retrieve the website’s IP address of 188.8.131.52.
- Without DNS, you would only be able to visit our website (or any website) by visiting its IP address directly, such as http:/184.108.40.206.
Finding the IP address of a domain name
For Windows OS users:
To open the Command Prompt, press the Windows key + R, then type cmd and click on OK:
In the Command Prompt window, type nslookup and press Enter. Type the website or domain (eg., www.google.com) name and press Enter:
The IP address of that website shows in the Addresses field, as shown in the preceding screenshot.
The firewall in the Domain Name system
A firewall is a piece of hardware or software that prevents malware and malicious attacks from entering a computer or a network of computers through the Internet.
Simply, the firewall monitors all this information traffic to allow “good data” in, but block “bad data” from entering your computer.
The three firewall scanning methods are packet filtering, proxy service, and stateful inspection Packet filtering blocks the incoming packet of information(a small chunk of data) if it is flagged by the pre-determined security filters Proxy service operates at the application layer of the firewall, where both ends of a connection are forced to conduct the session through the proxy.
A stateful inspection doesn’t rely on the memory-intensive examination of all information packets.
The firewall compares information being transferred to the copy relevant to that transfer held in the database; if the comparison yields a positive match, the information is allowed through, otherwise it is denied.
- A proxy server is an intermediary server between a client and the real server, which is used to filter or cache requests made by the client.
- It intercepts all requests to the real server to see whether it can fulfill the requests itself.
- If not, it forwards the request to the real server.
- There are many different types of proxy servers. Some common types of proxy servers are as follows:
- Anonymous proxy servers are used to conceal your information. When you go to request something from the web page, the web page gets the IP address of the proxy server that you’re using instead of your own.
- The server cannot access your IP address, and the communication between you and the proxy server is encrypted.
- Transparent proxy servers are used to forward your request to the resource that you want without concealing any of your information.
- Reverse proxy servers are used to pass requests from the Internet, through a firewall to isolated, private networks.
- It prevents Internet clients from having direct, unmonitored access to sensitive data residing on content servers on an isolated network, or intranet.
- It benefits the web server rather than its clients.