Hey guys. Welcome to Network Series Course from Alibaba Cloud. For this theory courses, we will have a comprehensive knowledge about the networks. Today is the first class and today's topic is about the Network Fundamentals. So we get started. Before we learn about the networks, the first thing that we should know is the OSI model. That's going to the first section and then learn about what is OSI model. So for OSI model, the full name For OSI is Open System Interconnection and we can see that OSI model is the basis of the network connection in the current time. OSI model is aimed to standardize in the communication between different systems. Because as we know for different systems, each of the system has its own protocol to make communication. So we need a standard to make it possible to communicate between different systems. For OSI model, seven layers of the data transmission has been defined in it and roughly we can define the seven layers into Data flow layer and the Application layer. We can see the picture on the right. From the bottom is the Physical layer and is the Data link layer, Network layer, and Transport layer. These four layers belong to the Data flow layers and in the upper layer is the Application layers. This include Session layer, Presentation layer and Application layer. So in the next, we will know that, what is the detail in each of the layers. So we come to the next page. Okay, so for this page, we can see that the lowest layer is the Physical layer. Actually, we can say that the Physical layer is the lowest layer in the OSI model and this layer is responsible for the wiring and the electric signal transmission and in the upper layer is the Data link layer. In this layer, all the data is transferred in frames. There's one thing that we should be familiar with, is the MAC address. In the Data link layer, the MAC address is used for location. So the upper layer is the Network layer, so for this layer the data is transported in packages. There is also one thing that we should be familiar with, is the IP address. In this layer, the IP address is used for location and the package will be transported according to their routing information. The upper layer is the Transport layer. For this layer, there is the one thing that we should be familiar with, is the TCP/IP protocol. Especially for TCP, it will ensure the data transport reliability and flow control. For this layer, it's responsible to make a reliable and stable connection between systems. Then, we come to the Application layers. For this layer, the first layer is the Session layer. In this layer, it allows different machine to establish sessions between them. So as we know that, If we are visiting some website, there will be a session that has been established between our client and the server operating system. So this is the thing that has been done in this layer. For the upper layer is the Presentation layer and this layer is responsible for the presentation of the data. Like if we want to show the picture we can use the JPEG, if we want to show the videos we can use the MP4 or AVI and if we want to show some text we use the ASCII code. This is what has been done in this layer. The highest layer is the Application layer. So this layer is used by the applications. This layer is end application programs or services used by end application programs. Like if we want to show the HTTP or some website we can use the HTTP protocol. If we want to connect some Operating System we can use the Telnet or SSH. So this is what this layer has done. So these are all the layers for OSI model. For this page, we're going to talk about the data encapsulating. The first thing that you should know is that data can only be transferred in one layer with corresponding package header. For example, if your data want to be transferred in the data link layer, your data should have back header. If your data want to be transferred in the transport layer, you should have the TCP header to be recognized by the corresponding protocol. That's why we say that the data should have the corresponding package header in each of the network layer. The second thing we should know is that no matter what data you have, basically, the data is transferred in the electric signal format, basically. We can say that all the data is transferred in the physical layer after all. We should know that in the application layer, if your data need to be transferred, your data is required to be encapsulated layer-by-layer from up to bottom before sending out in order to transfer in the physical layer, and that's the thing that we should clear. After we have know what is data encapsulating, we should know data de-encapsulating. As we know that the data has been transferred to the destination, and the application on the destination side will need to use the data. But we should know that the application will not recognize the data that has been added to some headers information. So this is not the original data. After the data has arrived at the destination, all the headers, the IP headers, the TCP headers will be removed from the bottom to top. First, there is the MAC, and LLC, and the IP headers, and the TCP headers, and then we can get the original data that can be recognized by the application. That's why we say that the data can only be recognized by the target application after all the data headers has been de-encapsulated. So we can just say, the data de-encapsulated is the reverse procedure of the data encapsulating. After we have learn about the OSI model, and also something about the data encapsulating and the de-encapsulating. For the second section, we're going to learn about some network protocols. In this section, we will have to know what [inaudible] the network protocols. Let's get started. The first protocol that we are going to learn about is the ARP. For the ARP, the full name is Address Resolution Protocol, and it is used to discover MAC address according to the IP address. Normally we are doing the communication with the IP address, but basically in the layer to network it is using the MAC address to find with each other. That's why we need to know their MAC address according to the IP address. For ARP, one thing we should know that it works in OSI data link layer app because data link layer is using the MAC address to do location. This is what we should know about the ARP protocol. The second protocol that we should know is the TCP protocol. The full name for TCP protocol, is the Transmission Control Protocol. This protocol is worked in OSI transport layer. In this layer is the fourth layer. What we should know about TCP protocol is that, this protocol is aimed to provide a reliable, ordered, error-checked data transferring via IP network, which means if we are using TCP protocol, you don't have to worry about whether the data has been transferred successfully or not, whether the data is lost or not. You don't have to worry about this one because TCP protocol will help you to do this kind of checking and verifying. So this is what TCP works. In the TCP protocol, it is using that IP plus Port to define a communication endpoint. If you want to find some place in the TCP protocol, and you have the IP address and the port. The last thing we should know that in the TCP protocol, connection must be established in a three-steps handshake process before entering the data transfer phase, which means the data is not directly start to transferring. Before the data transferring, it will have a three-steps of handshake process. After this handshake process, the TCP will verify whether the connection has been established successfully after this, and that this data will start to transfer. This how TCP protocol works. The next protocol that I would like to introduce you is the HTTP protocol. The full name for HTTP protocol is the Hypertext Transfer Protocol and as we know that HTTP protocol is working in OSI application layer. This is the highest layer in the OSI mode and HTTP protocol is aimed to exchange or transfer hypertext because as we know, hypertext actually we can say is the most widely used information format in the internet. So in some degree, we can say that HTTP protocol is the foundation of the data communication for World Wide Web. When the HTTP protocol is working, it functions as a request and a response protocol in the client server computing model to achieve information transferring. This is how achieve protocol works. After we have learned something about the network protocols, for the next section, we're going to learn about something that is very important, which is the IP address. As we know that normally we are using the IP address to do network communication. So let's get started. I think most of you guys have been very familiar about the IP address format. So here I will have a brief introduction about the IP address. First is that the IP address consists of four octets and for each octets it have eight bytes size number always ranged from zero to 255. For one IP address, it uniquely identify hosts or device in one network. This is some thing about the IP address. After we have introduced you the IP address, there must be something that we have to introduce to you together with IP address, which is subnet mask. Actually, we can say that the IP address must be combined with subnet mask because subnet mask is used to define a network bit and the host bit of one IP address. Even we can say if one IP address is the same, but if it's combined with different subnet mask, then IP address will appear located in different networks. So we should know that from the combination of the IP address and the subnet mask, we can get which network the IP address is located in. That's why we say that the subnet mask is very important to the IP address. The next thing that we should know is that subnet mask can be in format of dot-decimal notation like address format, like sum dot sum dot or in format of bit number from one to 32. For example, if we say that the subnet is in bit of 24 and the address format it is 126.96.36.199. So this is how the subnet mask works. After we have learned about the IP address and a subnet mask, we should know another concept is the IP address classification. All the IPv4 addresses has been classified into five part as class A, B, C, D, E. We should know that class A have the most IP addresses and class B to C to D to E, the quantity of the IP addresses will become less and less. Another thing that we should know is that just the class A and B and C can be used in the host environment, which means you can only configure the IP address in the class A, B and C, your own host or your own virtual machine, but you cannot use the IP address in the class D and E because these two classes have been reserved in some special conditions like multicast or some other special environment. So this is what the IP address classification is. So for IP addresses. There are another thing that we should know is that not all the IP addresses can be transformed in the internet. There are some IP address that has been reserved for private to use it. So here we can learn about what is those IP address for private usage. The first private network segment is the 10 dot segment. This is the class A segment. So this segment is used for internal use in the internal network environment. The second one is the 182.16231 base class B segment is also used for private. The last one is the 192.165 segment. This class B segment is also used for private usage. So this three IP address segment all use the four private networking environments like your own company network or your own enterprise internal network environment. Also, there are some special reserved addresses are also not used in the Internet. The first one is that the IP address is 169.154 class B segment. This segment is used for automatically private IP addresses use, for example, for sometimes maybe your machine or your server is doing the THCP but you cannot require some IP address. The IP address in this segment will be assigned to your computer. The next one is the 100.664 class B segment. So this segment is used for carrier-grade NAT Environment. This segment is reserved in the recent years in 2012, this year. After we have learned something about the logic that work, knowledge like IP address or network protocols. The last part, we are going to learn about some hardware and non agents for the networks. So let's get started. So for the first part is the Ethernet cables. Because, as we know that if we want to connect different systems, basically in the physical layer, we should connect with the cables. So in this page we will learn about something about the ethernet cables. So here we can say, in the worldwide scope. There are three network cables that is adopted in the worldwide scope. For the cat 5, this level of the Ethenet cable can just support 100 megabytes speed. For category 5E, and category six can support one gigabyte bandwidth. This is a difference between these three ethenet cables and for categories, six cables it has more powerful hardware specifications. It has a better quantity of the cable. So actually, we can say that a category six is the best quality network cable. For this page we have known some Ethenet standard from the 10 base-T to the 1000 base-zx from the top to bottom there standard become higher and higher. For each of the standard, it has defined a transmission media and the interface pipe, the maximum transmission distance and the speed. Here roughly, we can say that the fiber channel standard have a better standard than the category five or the RJ 45 interface. So we can say that the optical cable roughly have higher maximum transmission distance, also have higher transmission speed. For the last part we can know some hardware vendors in the network scope. Here, we can say many famous hardware vendors of the network devices like for Cisco, for H3C, for Huawei or ZTE, all of them is focused on the routing and switching devices. For Juniper and for Checkpoint, both of them is focused on the securities devices like firewalls and four F5 and radware and these two company is focused on the load balancer. So this is all the things about the network fundamentals. Thank you. Bye-bye.