 Welcome students, in this module I will talk about some very interesting things which consist of what and how to connect to an ISP, what is a database service provider, direct connection, indirect connection, what is in a domain server, what is in a domain name, how pages are generated, what is a web server, what is an application server, what is a database server. So, all of this will be explained using a diagram also and I hope you will take home many interesting things as per the today's module. So, let us deep go into the module and start with the module. So, you can see the list on your screen, how do we connect to the internet and connecting to an internet address, what is inside a domain and you can see all of this is interesting things, what is a web page, something very interesting, what is a session, what is a transaction, what is stateless, you may have heard these words a number of times. So, in this module I will explain what these terms are and what is the significance of these terms and how they are related and finally, what is a domain server, what is a web site, what is an internet site and where does the ISP comes in this whole picture. So, let us go into more detail. So, as you can see on your screen over here that we have indirect access and we have direct access. So, in the indirect access this is you and you are going through this router and this router is physically connected to the internet and that physical connection is using over a copper wire pair, over a fiber or over a cable TV depending upon what is available in your area. So, this is the indirect access. So, this is the direct access, you have your smart phone over here and this is directly connected to the internet or you are in your office or you are outside your office and this is a public Wi-Fi, maybe in a bus you are traveling in a bus as a public Wi-Fi and it connects to you to the internet. So, of course, these connection techniques have their own pros and cons, they have their own benefits. One of the biggest benefits of indirect access is it is shareable, it is sharing. So, because number of people are using it and you connected to it, it has high bandwidth also. This is another big advantage of indirect access. Direct access is on the go. So, it has its own advantages. So, you can see that we cannot say whether direct access is useful or indirect access is useful. It depends upon the application, it depends upon your requirements, it depends upon what you want to do, where you want to do it and how you want to do it. So, let us go into the more details over here. So, inside a domain name server. So, if you look at it, we have this routing tables, we have the central registry, we have the IP addresses and we have the mirror sites. So, what are all those things? Our domain name server is like a telephone book. So, it has in a telephone book or a telephone directory, we have the names of the people and we have their phone numbers and we have such electronic directory in our smartphones also or in our button oriented phones also. Because it is difficult for people to remember the names of other people with reference to the phone numbers. So, we remember the people by their names not by their phone numbers. So, in the routing tables what they do is they translate the domain name or the text that I type on it v u dot e d u dot p k into a string of numbers which the routing table translates. And of course, there are many routing tables depending on different ISPs and there is a central registry where all of this is compiled together. So, whenever anywhere in the world people are typing the text, the URL of the site where they want to go and corresponding to that site is an IP address which we had discussed in the prior module internet protocol address. So, these registries translate convert that text into an IP address. Now, what are mirror sites? Now, depending upon how much traffic is coming to a website, there may be duplicate sites mirror sites with duplicate data. Now, of course, it has its own issues of coherence reading and writing, but we are not going into it right now. It is not in the domain of this module. So, this is how it works. So, I have these multiple sites and these are mirror sites. So, what is a web page? Now, web page is something which comes before you. Now, contents of web page usually consist of text and within the text there can be images, it can be audio and there can be applets also. And it is the responsibility of the browser to interpret those web pages to convert those web pages into something interesting or something which was desired to be shown on your screen. It also contains a formatting information. Now, these web pages are generated by your client which is the browser and also by the application server which dynamically generates the web pages depending upon the query. It generates a page and it sends the page to you which is displayed on your screen. So, what is a session? What is a transaction? Now, when we connect, when my machine connects to the internet through a Wi-Fi connection, then I am the person who is being built for that Wi-Fi connection and that connection between my machine, my phone and the internet is called as a session. That is a session and a transaction is what happens between my web browser and ISP and to the other ISP and to the web server or to the application server. So, that is a transaction. That transaction contains all the information which is required to get the information, the formatting and everything to generate the web page before me. So, what is a database connection? Now, if you know what this is, we know this is. Now, what is this? In a database connection, maybe we need to login. When we login, we give the password, the connection is made and back and forth things are being sent and that is not a session, that is a transaction. And stateless means that the relationship between the transactions is not stored anywhere, the transactions are considered independent of each other. That is what means that web is stateless. That is all I have for this module. Thank you very much.