 Dear students, from today we are starting a new series of lectures or modules on networks. So previously we were discussing operating system and now we will start discussing in number of modules about the networks. You know that when different computers communicate with each other they can form a network. And there are different types of networks and how that kind of network can be classified we will learn in this module. So one of the classification of network could be area wise. So for example there could be a personal area network, local area network, metropolitan area network and wide area network. And these are abbreviated as PEN, LEN, MAN and WEN. So we will be discussing each and every kind of such systems and network classification in a little bit more detail. So what about personal area network? These are short range communications less than a few meter. For example you might have experienced a wireless headset which you wear with your smartphone. So you do not connect any cable with your smartphone and you are wearing a Wi-Fi kind of headset. Similarly you can also form a network under the category of PEN, personal area network when wireless mouse is installed on computer and used. So for example you might have seen that there are certain mouse available which do not need any cable. So they are even connected with a Wi-Fi. So such kind of small ranged networks are examples of personal area network. And then local area network is a collection of computers in a single building. So for example computers in university campus, some manufacturing plant. So there is a building, huge building. So in that building whatever computers are connected, so all of such computers are categorized as connected in LAN, local area network to form a local area network. And then metropolitan area network MAN is basically network of intermediate size, some comprising of local community. So for example digital network based surveillance system of a city. So the whole city is basically being viewed or watched by the surveillance team and all of the cameras are connected together to form a network. And then for example parking system interconnected across the whole city. So such a community if connected form MAN. And then wide area network is basically links machine over a greater distance in neighboring cities. So for example you are connecting different cities together and connection using the internet. So we will learn it in the next slides what is internet. So this was one of the classification that is based on the area. And then there is another classification that is based on open versus closed connections network connections. So for example open network is networks internal operation is based on design data in the public domain. For example the internet which is used by the public. And there could be some close networks. So for example those innovations owned and controlled by a particular entity. For example some individual or a corporation or some security agencies. So who have formed their own very dedicated and close network. So anyone from outside that network cannot enter and if and if that user enters that is an unauthorized access. Then there is another type of network classification based on the topology topology mean that how the computers are connected together. So for example there could be number of computers who are connected with one line. There could be another way that for example one computer is serving as the main and then all other computers are connected to that particular central focal point. As we discussed in the start of the modules about client and server kind of architecture where different terminals were accessing the same server. So there are basically two types mainly which we will be discussing here bus and start apologies. Here is a little bit better visualization of these topologies. So in bus we have multiple computers and those computers are connected through this one line and this was popular in 1990s when implemented in standard as Ethernet. And then the start apology where here is a main computer maybe it's a server or some focal point computer and all other computers are connected with this access point or computer. This is also sometime called an access point and it has roots in 1970s when one focal point computer and many terminals were available. So if we summarize today's module we have learned about network classification based on the area based on the open and closed access and based on the topologies in the form how the computers are connected together to form a network.