This is a group of computers in a small area, which is linked via a LAN. It cannot extend further than the restrictions of a single building. Computers on the LAN are called nodes. A LAN is known by three attributes: its topology, its medium, and its protocols. The topology is the pattern used to connect the computers together. With a bus topology, a network cable connects each computer to the next one, creating a chain. With a star topology, each computer is connected to a central nexus called a hub. A ring topology is a bus network with the two ends joined together.
The link between the systems, on the network is the network medium. The topology and the medium used on a certain networks are specified by the protocol functioning at the data-link layer, e.g. Ethernet or Token Ring. Ethernet supports a few topologies and media. Whatever grouping of topology and medium is used for a LAN should be used on all the other computers in the same LAN or building. There are hardware products that allow you to join computers to the same LAN with different media. You cannot hook up a bus Ethernet system to a star Ethernet system and the systems are part of the same LAN or building in which it is situated. All of the systems on a LAN must share the same protocols. You cannot connect an Ethernet system to a Token Ring system on the same LAN.
Wide Area Network
When you are connected to the Internet, you are connected to the largest Wide Area Network (WAN) on earth. A WAN is a network that crosses metropolitan, regional, or national boundaries. The people usually think of the WAN as a network that uses routers and public network links. WANs differ from LANs in the following ways:
• WANs cover greater distances.
• WAN speeds are slower.
• WANs can be connected on demand or it can be connected permanent; LANs have permanent connections between stations.
• WANs can use public or private network transports.
• Use private network transports.
The communication the WAN is using is either full- or half-duplex. LANs use half-duplex communications, but usually the local area network uses full-duplex communications. The Internet is a specific type of WAN. The Internet is a collection of networks that are interconnected and, is theoretically an inter-network. A WAN can be centralized or distributed. A centralized WAN consists of a central system to which other systems and dumb terminals are connected. The Internet consists of interconnected systems in different locations.
Broadband and Base-band
LANs (in a building) use a network medium that is shared. The cable that is used only takes one system at a time, and the systems should take turns using the LAN. This setup is called a base-band network. The information that the systems broadcast is broken up in units are called packets. When an e-mail message it might be broken up into many packets, and the computer transmits each packet separately. When all of the packets that make up a particular transmission reach their goal, the system that is receiving the information reassembles it to the original e-mail. This is the basis for a packet-switching network.
The alternative to a packet-switching network is a circuit-switching network. Circuit switching means that before two systems can communicate they first create a circuit before sending out any information. That circuit remains open during the existence of the exchange, and is closed when the two systems are finished communicating. This is a non-sensible answer for computers on a base-band network, since two systems could conceivably monopolize the network medium for long periods, which will stop the other systems from communicating. Circuit switching is more appropriate in surroundings like the public switched telephone network (PSTN).
A broadband network is the opposite of a base-band network. It carries numerous signals in a single cable at the same time. A cable TV (CATV) service runs a single cable into a user’s home, but that one cable carries the signals for dozens of TV channels and often carries Internet access. Broadband technologies is usually used for wide area networking than local area networking.
Half-Duplex and Full-Duplex Communications
When two computers broadcast over a LAN, data travels in one direction at a time. Base-band network are usually LANs that support only a single signal, which is called half-duplex communication. Systems that transmit in both directions at the same time are usually in full-duplex mode. Examples of a full duplex network are the telephone line, and an example of a half duplex system is a CB radio.