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A data communications network is a collection of terminals, computers, and other equipment that use communication channels to share data. Network can be classified as Local Area Networks (LAN), Wide Area Networks (WAN), Metropolitan Area Networks (MAN), or even Personal Area Networks (PAN). The use of distributed processing and networks allow an organization to place its computing power in optimal physical locations to meet the information processing needs of its end users, as well as those of the entire organizations.
Local Area Networks (LAN) is usually smaller scope networks that provide a high-speed data rates in physical and logical connection among a group of stations. They typically encompass a walk-able geographic area, owned and administered by the user and are mainly used either for hardware sharing or as access networks for greater geographical scale. Most commonly used LAN is the Ethernet. Since then, the latest technology has produced switched systems and Asynchronous Transfer Mode (ATM).
Wide Area Networks (WAN) cover a general or bigger geographical area that may vary from a small office area. Usually, network providers and big businesses own this type networks. WAN are mostly heterogeneous, or can be define, a large variety of LAN and equipments or other WANs can constitute a single WAN. An example of a WAN is the Internet. Internet spans much of the populated world, is administered by different groups at different locations, and has many other WANs as part of it. Most of WAN technology is circuit switching, frame relay, and Asynchronous Transfer Mode (ATM).
Metropolitan Area Networks (MAN) are networks between a LAN and WAN. They are a type of interconnecting networks for big businesses in a metropolitan area. Usually, they have interconnecting (switching) devices instead of user desktop computers as their nodes, but it is possible to have user computers directly attached to a MAN.
One way to differentiate among LANs, WANs and MANs is the way transmission resources are accessed. Typically, LANs have uncontrolled shared medium, MANs are controlled shared medium access, and WANs have address-based, switched medium access through a separate network. There are other types of networks in this classification. More recently, the term personal area networks (PANs) has got legitimacy in networking literature due to the fact that they can be distinguished from other three types. PANs are networks interconnecting the devices of personal use that could, in general, be carries around. Examples of such devices are personal digital assistant (PDA) android and smart phones, various wireless phones, remote control, and many more. Usually, the design of these networks entails replacing the wire only, as they aren't expected to be interconnected via WANs and MANs in near future.
Topology can be defined as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home connection of LAN can be arranged in a circle in a house, but it would be highly unlikely like circle than known as ring topology. Network topologies are categorized into the following basic categories:
There are more complicated layout of networks that is be built as hybrids of two or more of the above basic topologies.
Bus networks are usually used in a common backbone to connect all devices. The bus networks layouts is designed or connected by a single cable, the reverse functions as a shared communication medium that connecters attach or valve into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message but, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable. In example explanation, if a message is needed to send to specific location, it must needed to identify target station because each stations as a specific address. Besides that all bus connections are full duplex between the stations, so that it allows the transmission and reception in balance conditions. Bus network topology is needed to regulate transmission, so that it will not cause collision and hogging.
In a ring network, every computer can have two neighbors for communication purposes. All messages pass through through a ring in the same direction in either "clockwise" or "counterclockwise". A failure in any cable or device breaks the loop and can take down the entire network. The data of each frames move in circulation by pass through all stations. By having a sort ââ‚¬Å“tokenââ‚¬ that is used whereas destination recognizes address and copies frame. This particular frame will keep circulates back to source where it is removed.
Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.
Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)
Illustration - Star Topology Diagram
Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.
Illustration - Tree Topology Diagram
Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.
A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.
Illustration - Mesh Topology Diagram
Wireless Local Area Networks
A wireless LAN (WLAN) is much like a wired LAN except that it employs little or no wiring. An access point replaces the hub. All wireless terminals communicate with each other via the access point. Sometimes, we distinguish between two types of WLANs based on the use of an access point. A WLAN with an access point is called an infrastructure network. A WLAN without an access point is called independent network or ad hoc network. In an independent WLAN, the terminals communicate directly with each other without the access point. There are many WLAN architectures used worldwide, some are proprietary and others are industry standards. Examples of standards are the HIPERLAN proposed by European Telecommunications Standards Institute (ETSI) and IEEE802.11 recommended by the 802 committee of the Institute of Electrical and Electronic Engineers (IEEE802). In this third example of network architectures, we will have a look at the reference model of the IEEE802.11. Figure 2-10 shows a general schematic of an infrastructure WLAN and Figure 2-11 shows the protocol architecture of the IEEE802.11 WLAN.
Topologies remain an important part of network design theory. You can probably build a home or small business computer network without understanding the difference between a bus design and a star design, but becoming familiar with the standard topologies gives you a better understanding of important networking concepts like hubs, broadcasts, and routes.