INTERNET AND ITS SOFTWARE   COMPONENTS 

The Internet has two major components: network protocols and hardware. The most prominent component of the Internet model is the Internet Protocol (IP). IP enables internetworking and establishes the Internet itself.

The basic components of the Internet are: Client, Server, Protocols.

The protocols are crucial elements of the internet. They present sets of rules that devices must follow in order to complete tasks. Without these rules, machines would not be able to communicate.

Some examples of Internet software include: Google Chrome, Mozilla Firefox, Internet Explorer.

Software is the computer programs that run on the system, like Microsoft Windows or Microsoft Word.

After through some of the basic networking concepts, let us now look into some more concepts relating to one of the major application of networks the Internet. You have been introduced to internet in section 1.2.2. Let us once again sketch some of the basic points on Internet.

• Internet is a global connection of networks. But, how are these computer connected? The Internet is basically built up of multiple smaller networks called the subnets. Each computer systems on a subnet must have a unique address. All these subnets are connected together with network devices called routers, and each subnet may also contain its own subnets. 
• Figure 1.22 is a top level view of the structure of the Internet as a cloud of many routers that are connected to each other. You may be able to connect to any of the search engines that allows you to locate information on Internet or any of the web servers like IGNOU web server through many alternative routes. A client may be a part of LAN, WAN or wireless network, it does not matter. Everything is almost in the Internet cloud -why? Because all these networks use one common protocol for reliable data transfer, so they speak common language and communicate irrespective of physical differences. This basic communication protocol on Internet is the Transmission Control Protocol/ Internet Protocol (TCP/IP). This protocol ensures reliable delivery of information from one source identified by a unique IP address to a destination also identified by a unique IP address. Please note that the source and destination computer may either be local or remote computer, depending on the destination location. But what are these IP addresses?

• To connect to a physical network, all devices irrespective of being wired or wireless uses an interface card. An interface card may have its own unique physical address. However, you cannot locate a device just by its unique physical address, as these addresses do not provide any indication about the location of the device. Thus, you require a protocol that uniquely identifies a device on the Internet and Internet protocol version 6 (IPV6) which is beyond the scope of this unit.
• TCP and IP (TCP/IP) are the two core protocols of the Internet Protocol suite. The TCP primarily provides the reliable delivery of stream of bytes from a computer or a program to another computer or a program. It breaks the data stream into packets at the source and makes sure that all the packets are assembled orderly at the destination. The IP protocol on the other hand identifies the location of source and the destination. Any computer on Internet is identified by its unique IP address. Currently two standard versions of IP are available viz. Internet Protocol Version 4 (IPv4) which is currently being used on most of the Internet. An IPv4 address is a 32 bit address. IPv6 has not been discussed in this Unit.
• Using the TCP/IP as the basic protocol Internet offers many services and application to it users like work wide web, Email, Chat, Social networking, collaboration etc
• WWW is one of the major applications of Internet and is based on the concept of Hypertext that is hot links to a document that may reside on any website. It is a global infrastructure of connected documents. Following are some of the major Software Components required to access Internet:
• The first software for internet access is the Operating system. An operating system must be installed properly on your system (so that it can handle the driver requirements of the hardware components).  
• Internet Browser: Browser is software that allows the user to access and read information on the World Wide Web. Internet Explorer, Mozilla, Netscape are the best-known browsers. Space Time 3D is new three dimensional browser. Only browser is sufficient for working with the Internet viz., the browser software that should be loaded on all the clients. In fact, the browser is one of the very intelligent software that contributed to the growth of World Wide Web. A browser converts the standard Hyper Text Markup Language (HTML) web pages to a very sophisticated display with colors and pictures.
• Firewall: Internet has many security problems like hacking, Trojan Horse, Virus, etc. There are various tools to provide protection against unwanted access of your computer by anyone else, but the most popular among all security measures is the firewall. Firewall is software that works on some set of rules and instructions given by you. A firewall helps to keep your computer more secure. It restricts information that comes to your computer from other computers, giving you more control over the data on your computer and providing a line of defense against people or programs (including viruses and worms) that try to connect to your computer without invitation.
•  TCP/IP protocol: This is the group of protocols that define the Internet and communication method used by it. Let us discuss it in more details :

TCP/IP Stack

TCP/IP was originally designed for the UNIX operating system; however, TCP/IP software is now available for every major operating system. In order to be compatible to the Internet, the computer must have TCP/IP compatible software. The major advantage of Internet is information sharing. Since in computers, bits and bytes are basic building blocks of information. Thus, one of the key aspects in network of many computers is to move bits between two specific computers. For such a communication, we require the address of the destination and a safe mean of moving data in the form of electronic signals. As far as safe movement of data is concerned, there exists a set of rules, which governs the sending, and receiving of data on the Internet. 

A stack of protocols called TCP/IP (Transmission Control Protocol/Internet Protocol) implements these rules. Its name reflects names of only two protocols called TCP and IP. For sending large block of text/data to another machine, TCP divides the data into little data packets. It also adds special information e.g., the packet position, error correction code etc. to make sure that packets at the destination can be reassembled correctly and without any damage to data. The role of IP here is to put destination addressing information on such packets. On Internet, it is not necessary that all the packets will follow the same path from source to destination. A router tries to load balance various paths that exist on networks. Other gateways allow different electronic networks to talk to Internet that uses TCP/IP. 

The Internet layer is an important layer in the protocol suite. At this layer, TCP/IP supports Internet Protocol (IP). This layer is responsible for the format of datagram or a packet as defined by IP and routing and forwarding a datagram or packet to the next hop (hop is a term that can be used to represent any computing device on Internet like; router, gateway, computer etc. A hop is the trip from one device to the next.) The primary goal of the Internet is to provide an abstract view of the complexities involved in it. Internet must appear as single network of computers. At the same time network administrators or users must be free to choose hardware or various internetworking technologies like Ethernet, Token ring etc. Different networking technologies have different physical addressing mechanisms. Therefore, identifying a computer on Internet is a challenge. To have uniform addressing for computers over the Internet, IP defines an IP address, which is a logical address. IP address is a 32 bits number, can be represented in decimal e.g., 192.168.32.10. Now, when a computer wants to communicate with another computer on the Internet, it can use logical address and is not bothered with the physical address of the destination and hence the format and size of data packet. IP address is a basic address used by the lower architecture of Internet. It is important for you to know that, any address you type as web address or email address actually gets converted into the equivalent IP address of a machine or computer where the server or resource is available. Web address or email addresses are used for ease and convenience of human beings otherwise; it is just a burden for network.

TCP/IP Model 

Just like the OSI model, the TCP/IP model has many layers which are described below:

Host to Host Network: In fact TCP/IP model does not specify this layer. But it basically combines functionally of physical and data link layers. Starting at the bottom, the Physical layer is what deals with hardware (wires, cables, satellite links, NICs, etc.). Utilizing the existing Physical layer, TCP/IP does not define its own, thus letting the layer be compatible with all network suites. This layer also encodes and transmits data over network communications media in the form of bits which are received by the Physical layer of the destination device. Often combined with this layer is the Data link layer which is responsible for moving packets from the network layer onto different hosts. Depending on the connection type, IP packets are transmitted using various methods. Dial-up modems transmit IP packets using PPP while broadband users transmit using PPoE.  

Figure 1.23 : TCP/IP Model

Internet Layer: This layer routes and delivers data across similar networks or completely different networks. The Network layer is responsible for end to end packet delivery while maintaining routing, flow control, and error control functions. An example of this layer is the Internet Protocol (IP) or the Internet Protocol Security (IPSec).

Transport Layer: The Network layer can be thought of the actual vehicle which transports information. This layer categorizes end to end message transmissions or connecting applications as either Transmission Control Protocol (TCP) or User Datagram Protocol (UDP). TCP is a connection-oriented protocol which is considered to provide a reliable byte stream. Some characteristics of TCP are traffic congestion control, data arrives in order, data has minimal error, and duplicate data is discarded. 

The top layer of the TCP/IP model is the Application layer which is used for network communication. Ports are used by programs to transfer data through this layer. For example, the File Transfer Protocol uses port 21 by default while the Hypertext Transfer Protocol uses port 80.

TCP/IP has many benefits. TCP/IP enables cross-platform networking which is useful in this day-in-age. This suite also has superior failure recovery and the ability to add networks without interrupting existing services. The reliability of TCP/IP is also a huge benefit to using this protocol. The fact that if one part of the network goes down, other parts are still able to function is what has set TCP/IP above other networking protocols. TCP/IP is also easily expandable which allows for the unprecedented rate of growth which the Internet possesses.