I Introduction Computer networks are some of the computers that are interconnected in some way for the purpose of exchanging information for one another with the advantages of: Many people can share a peripheral (printer, modem ..), a software. Data is centrally managed so it is safer, the exchange of data information between users will be faster, more convenient. Users can exchange messages with each other easily and quickly. It is possible to install the Internet on any computer in the network, then set up, configure the other machines can through the machine has installed Internet share program to also be able to connect to the Internet. II Computer network classification Computer networks can be distributed in different areas, one can split the network types as follows: Local Area Network (LAN) is a local area network that connects computers in a narrow radius, usually around a few hundred meters. High-speed communication media, such as twisted pair, coaxial cable, fiber optic cable. LANs are often used internally by an organization, an organization. LANs connect to each other as WANs. WAN (Wide Area Network) is a wide area network that connects computers within the country, or between countries in the same continent. Normally this connection is made through telecommunication network. The Wan connected to GAN. The Global Area Network (GAN) connects computers from different continents. Often this connection is made through telecommunication and satellite networks. MAN (Metropolitan Area Network) Connect computers within a city. Connections are made through a high-speed communication medium (50/100 Mbps). III You should have a network Depending on the total number of computers, the total number of devices you will use. Maximum distance between devices. Here we discuss only the local topology LAN. This is the most used network. Local Area Network (LAN) is a network with high-speed communications, designed to connect computers together in a small geographic area such as a building, a school. You can share resources such as printers, CD-ROM drives, software applications such as just one machine in the network installed Share Internet program, the other can still connect to the Internet. This will meet the need that when in your office once the computers are connected to the LAN and every user wants to access the Internet and other Internet services ...., You only have one modem and one Internet account. Installation solution for each machine a modem, pulling each machine a phone line is too expensive, or if anyone wants to access the Internet, installing a modem on his machine and connecting the phone to it is very inconvenient if it is. Built-in modem, or phone line too short, etc. To solve this problem, the Proxy Server emulation software is formed. The effective software in internet sharing are Wingate, WinRoute, WinProxy, ISA Server ... IV Introduction to Star Topology: The star network consists of a central point and information nodes connected to that central point. Information nodes are terminals such as computers, or other network devices. At the heart of the network is the main coordinator of all network activities with the following functions: Forward data between nodes (computers together). Get to know the state of the network, the nodes (computers) are connected to the network. Monitoring and handling during information exchange IV Advantages and disadvantages of star network: Advantages of star network: Operating on the principle of parallel connection, so if any device on any node is broken, the network is still operating normally, the remaining machines are still operating normally. It is a simple, structured and highly configurable network. Networks can be expanded or narrowed according to user requirements Disadvantages of star network: Network expansion depends on the capabilities of the central device. If the central equipment fails, the whole network will be paralyzed. The maximum distance from the nodes to the center is limited (less than 100m). The necessary equipment in the star network: Central equipment: can use HUB or Switch. Connection cable: twisted cable. Network Interface Card (NIC) for each node. There are so many different types of network cards you can choose from depending on your finances. V General model of a Star topology:
