This lecture introduces the basic concepts of computer communications. It covers the basic concepts of computer networks starting from LANs (local area network) to WANs (wide area networks). It introduces how LAN, MAN (Metro Area Network), and WAN can exchange information between stations attached to them. Also the basic concepts of addresses in computer networks will be covered such as MAC (media access control), SAP (service access point), IP (Internet Protocol), and port addresses. In addition, flow controls and error controls in various layers will be also covered. Mechanisms of MAC and logical link layers will be introduced too. New concepts such VLAN, VPN, and Internet will be also covered. Internet protocols from IPv4 to IPv6 will be treated with routing algorithms. Transport layer concepts, basic core functionalities, protocols, and standards related to computer networks will be covered. Concepts such as connection oriented and connection less will be included too. Network devices such as bridges, hubs, routers, and various switches will be introduced and compared.