Components of Network
LANs do not use the telephone network. Its networks are constructed with standard set of components. As discussed below:
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- All networks need some system for interconnection. In some LANs, a shared network cable connects the nodes. Low-cost LANs are connected with twisted wire pairs, but many LANs use coaxial cable or fiber optic cable, which are both more expensive and faster. Some LANs are wireless, using infrared or radio wave transmissions instead of cables. Wireless networks are easy to set up and reconfigure, since there are no cables to connect the devices, but they have slower transmission rates and limit the distance between nodes.
- A network-interface card (NIC), connects each computer to the wiring in the network. NIC is a circuit board that fits in one of the computer’s internal expansion slots. Some computers have built in NIC.
- Similar networks can be connected by a bridge, which recognizes the messages on a network and passes on those addressed to nodes in other network.
- A gateway is a collection of hardware and software resources that lets a node communicate with a computer on another different network. A gateway, for example, could connect an attorney on a local area network to a legal service offered through a wide-area-network (WAN will be discussed after this topic).
- A router is a device that connects two or more networks it consist of a combination of hardware and software. The hardware can be a network server, a separate computer, or a special black box device. The hardware includes the physical interfaces to the various networks in the internetwork. These interfaces can be Token Ring. Ethernet, TI, Frame Relay, asynchronous transfer mode (ATM), or any number of other technologies. The two main pieces of software in a router are the operating system and the routing protocol. Management software can be another software component of a router.
LAN’s Protocols: networks have certain rules, called Protocols, to send and receive data, and it is defined in the network software. The most common of them are explained as under:
- Ethernet: currently, this is the most commonly used protocol. It uses a high-speed network cable and bus topology, so it is relatively simple and cheaper. Since all the nodes (computers) use the same cable to send and receive data, they must follow a set of rules about when to communicate, otherwise, two or more computers could transmit at the same time, causing lost messages. Before transmitting the data, a node listens” to find out if the cable is in use. If so, the node must wait. When the cable is free from other transmission, the node can begin transmitting immediately. This process is also known as CSMA/CD (Carrier sense Multiple Access with Collision Detection).
- If by chance, two nodes transmit data at the same time, the messages collide. When a collision occurs, a special message, lasting a fraction of a second, is sent out over the network to indicate that it is jammed. Each node stops transmitting, waits a random period of time, and then transmits again. Since the wait period for each node is random, t is unlikely that they will begin transmitting at the same time again.