Билет № 9

Прочтите и переведите письменно со словарем ИИТУ

Network Structures

A network is a way to connect computers for communication, information exchange, and resource sharing. The four most important benefits of networking are simultaneous access to programs and data, peripheral sharing, streamlined communications, and easier backups. E-mail, videoconferencing, and teleconferencing are examples of the personal communications that can be conducted over a network or the Internet. Networks can be categorized in different ways, such as by geography (how much terrain they cover) or by the use or absence of a central server. A local area network (LAN) consists of computers that are relatively near one another. A LAN can have a few PCs or hundreds of them in a single building or in several buildings. On a network, data is broken into small groups called packets before being transmitted from one computer to another. A packet is a data segment that includes a header, payload, and control elements that are transmitted together. The receiving computer reconstructs the packet into the original structure. The payload is the part of the packet that contains the actual data being sent. The header contains information about the type of data in the payload, the source and destination of the data, and a sequence number so that data from multiple packets can be reassembled at the receiving computer in the proper order. Each LAN is governed by a protocol, which is a set of rules and formats for sending and receiving data. TCP/IP, IPX/SPX, and NetBEUI are examples of network protocols. LANs can be connected by a bridge or router to create a much larger network that covers a larger geographic area. To connect LANs, a gateway may be required to enable them to share data in a way that the different LANs can understand.

Билет № 10

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Network Topologies

A topology is the physical layout of the cables and devices that connect the nodes of a network. The three basic topologies are bus, star, and ring. These topologies are so named because of the shape of the network they create. The less common type of physical topology is the mesh topology. The bus network uses a single conduit to which all the network nodes and peripheral devices are attached. Each node is connected in series to a single cable. At the cable's start and end points, a special device called a terminator is attached. A terminator stops the network signals so they do not bounce back down the cable. The star network is the most common topology in use today. In a star network, a device called a hub is placed in the center of the network; that is, all nodes are connected to the central hub and communicate through it. Groups of data are routed through the hub and sent to all the attached nodes, thus eventually reaching their destinations. Some hubs known as intelligent hubs can monitor traffic and help prevent collisions. In a star topology, a broken connection (between a node and the hub) does not affect the rest of the network. If you lose the hub, however, all nodes connected to that hub are unable to communicate. The ring topology connects the nodes of the network in a circular chain, with each node connected to the next. The final node in the chain connects to the first to complete the ring. With this methodology, each node examines data sent through the ring. If the data known as a token is not addressed to the node examining it, that node passes it along to the next node in the ring. The mesh topology is the least used network topology and the most expensive to implement. In a mesh environment, a cable runs from every computer to every other computer. If you have four computers, you must have six cables – three coming from each computer to the other computers.