networking

The internet consist of a worldwide interconnection of govermental, academic, public and private network based upon the networking technologies of the internet protocol suite. The internet is also the communications backbone underlying the world wide web (WWW). THE OPEN SYSTEM INTERCONNECTION REFERENCE MODEL (OSI) is an abstract description for layered communications and computer network protocol design .It divides network architecture into seven layers: application layer Presentation layer Session layer Transport layer Network layer Data link layer Physical layers All networks are made up of basic hardware building blocks to interconnect network nodes such as network inteface cards, bridges, hubs, switches and routers. A network cards, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often a provide a low level addressing system through the use of MAC addresses. A repeater is an electronic device that receives a signal and retransmits it at a higher power level or to the other side of an obstruction so that the signal can cover longer distances without degradation. A network hub contains multiple ports. When a pocket arrives at one port, it is copied unmodified to all ports of the hub for transmission. A network bridge connects multiple network segments at data link layer (layer 2) of the OSI. Bridges do not promiscously copy traffic to all ports,as hub do, but learn which mac addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address only to that port. A network switch is a device that forwards and filters OSI layer 2 datagrams between ports (connected cables) based on the MAC address in the packets. This is distinct from hub in that it only forwards the packets to the ports involved in the communications rather than all ports connected. A switch is not capable of routing traffic based on IP adress (OSI layer 3) which is is necessary for communicating between network segments or within a large or complex LAN. A router is a networking device that forwards packets between networks using information in protocol headers and forwarding tables to determine the best next router for each packet. Routers work at the network layer of the OSI model and the internet layer of TCP/IP. Data transmission is possible in three modes. Simple: transmission is possible in only one direction Half duplex: transmission is possible in both direction but not simultaneously Duplex: transmission is possible in both directions simultaneously