The beginning of the Internet is said to be 1969.In 1969, the US Department of Defense began building a computer network called the ARPANET (Advanced Research Projects Agency NETwork) throughout the United States.Four universities and research institutes (University of California, Los Angeles (UCLA), University of California, Santa Barbara) have dedicated data communication networks that use packet exchange technology to divide data into packets and send them instead of using the telephone network for line exchange. The experiments were conducted interconnected at the school (UCSB), Utah University, and SRI International.And we have realized mail and file transfer between two or more computers.In 1990, ARPANET was taken over by the National Science Foundation (NSFNET).At that time, the prototype of TCP / IP currently used on the Internet was applied as the communication procedure.Figure 1 shows the basic configuration of the current Internet.It divides the data from terminal A to terminal B and sends an IP packet in packet format.IP packets are first sent to the router via LAN (Local Area Network).After that, it will be sent to the entrance of the other network via some networks, and will be sent to terminal B via LAN.A router is a device that connects a network and determines to which side the received packet is sent.Originally, in inter-computer communication, the OSI (Open Systems Interconnection) reference model that realizes data communication between different models established by the International Organization for Standardization (ISO) in 1984 is common as its protocol (communication standard). bottom.But on the internet ...Last time, I introduced familiar networks such as the Internet.This time, we will focus on LAN.LAN is a Local Area Network, which is a network that interconnects computers in a building with high-speed lines.The Ethernet standard is a typical LAN standard.This article introduces LAN transmission media, computer connection modes, and devices that connect LAN to LAN.Ethernet is a type of LAN that complies with the IEEE international standard specifications.Developed by the Palo Alto Research Center of Xerox in the United States in 1973, it was subsequently standardized as the IEEE 802 standard.Recently, Fast Ethernet with a communication speed of 100 Mbps and Gigabit Ethernet that enable communication of 1 Gbps or more are becoming widespread.Table 1 shows the typical transmission media for Ethernet: coaxial cable, UTP cable, optical fiber, and wireless LAN.A typical bus-type LAN access control is the CSMA (Carrier Sense Multiple Access) method.With the CSMA method ...Ethernet data is transferred in the form of Ethernet frames (MAC frames) and contains a 48-bit destination MAC address and a 48-bit source MAC address.It works in the same way both inside the LAN and when connecting the LAN to the LAN.Devices that connect LANs include repeaters, repeater hubs, bridges, and switching hubs.Last time, I introduced the basic knowledge of LAN.This time, we will focus on IP technology.TCP / IP is known as the basic technology of the Internet.TCP checks to see if the data is coming correctly between the source computer and the destination computer (more on that next time).In addition, IP technology is a basic technology that connects multiple networks and seeks the optimum route in order to deliver data from the source to the other party.IP (Internet Protocol) is a protocol (transmission procedure) that is the basis of data transfer in TCP / IP, which is widely used on the Internet, and realizes data transmission between multiple networks.The function of transferring data across multiple networks is called routing or route control.A device with this function is called a router (or switch).An IP address is a unique address given to each host for route control.Like addresses on the Internet, they are assigned to devices on the network such as smartphones and PCs.The MAC address described in the LAN last time is used in one or more LANs.IP addresses, on the other hand, are common to all networks.Conversely, without an IP address, the source computer cannot send to the destination computer over multiple networks.Currently, there are IPv4 and IPv6 IP address versions.Of these, IPv4, which is widely used, uses a 32-bit integer as the IP address.As a notation, the decimal system with a decimal point is often used.This is a notation method in which 32 bits are divided into 4 by 8 bits, and each is expressed in decimal (0 to 255) and connected by a period.For example, if the IP address is 192.168.10.32, it will be expressed as shown in Figure 3.An IP address consists of two parts: a network address part that indicates the address of each network, and a host address part that indicates the address of a host (computer) in the network (Fig. 4).In this case, how do you separate the network address part and the host address part?In IPv4, when the network address part is 8 bits, 16 bits, and 24 bits, they are called class A, class B, and class C, respectively.The format of the IP address is shown below.The subnet mask is a numerical value used to divide an IP address and identify what is the network address part and what is the host address part represented by the computer.If IP addresses are assigned in units of class A, class B, and class C explained in the previous chapter, the number of IP addresses will be insufficient.Therefore, the subnet mask determines the range of IP addresses in a slightly more detailed manner.Hosts on the same network have the same network address part, and the subnet mask shown below indicates how many bits of the IP address are the network address part.Conversely, if you know this subnet mask, you can know what part of the IP address is the network address part.The router looks at the network address of the destination and decides the output port.There are two ways to express the subnet mask.© 2015-2022 IPROS CORPORATION. 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