Operating Systems
Tuesday 06 December 2011 at 1:35 pm.
Network operating systems have a wide variety of shapes and sizes, because each organization that employs them has different needs. Some operating systems behave excellently on small networks, and others specialize in connecting many smaller networks rather broad areas. The services performed NOS are: Support for files: that is, create, share, store and retrieve files, essential activities that specializes NOS providing a quick and secure.
Communications: This refers to everything that is sent through the cable. Communication takes place when, for example, someone enters a network, copying a file, email, or print. Services support team: This includes all special services like printing, tape backups, virus scanning on the network, and so on. Back to topics in this section network topology network nodes (computers) need to be connected to communicate. The way in which nodes are connected is called topology. A network has two different topologies: one physical and one logical. The physical topology is the actual physical layout of the network, the way in which the nodes are connected to each other. The logical topology is the method used to communicate with other nodes, the route taken by network data between different nodes of the same. Physical and logical topologies may be identical or different. The most common network topologies are: bus, ring and star. Red bus in a bus topology, each computer is connected to a common segment of the network cable.
The network segment is placed as a linear bus, ie a long cable that goes from one extreme to another network, and which connects each node of the same. The cable can go through the floor, the walls, ceiling, or can be a combination thereof, provided that the cable is a continuous segment. A ring network ring topology consists of multiple nodes together to form a logical circle. Messages are moved from node to node in one direction. Some networks may ring in a two-way messaging, however, are only able to send messages in one direction at a time. The ring topology allows to check if a message is received. In a ring network, the workstation sends a data packet known as arrow or passkey. Red Star One of the oldest types of network topologies is the star, which uses the same method of sending and receiving messages to a phone system, since all messages in a star topology LAN must pass through a central device called connection wiring hub, which controls the flow of data. Back to topics in this section Network architecture networks are composed of many different components that must work together to create a functional network.The components comprising the hardware portion of the network include network adapter cards, cables, connectors, hubs, and even the computer itself. Network components make them, usually several companies.
Therefore, there must be understanding and communication between the manufacturers in relation to how each component works and interacts with other network components. Fortunately, we have created standards that define how to connect hardware components and network protocol (or rules) to use when establishing network communications. The three most popular standards or architectures are: ARCnet, Ethernet and Token Ring. Ethernet and Token Ring are supported standards organization IEEE (Institute of Electrical and Electronics Engineers), while ARCnet is an industry standard that has recently become one of the standards of ANSI (American National Standards Institute). ARCnet Networks Produced in the seventies by Datapoint Corporation, the network of connected computing resources (ARCnet) is a standard accepted by the industry, but does not carry a standard number of IEEE. ANSI recognized standard ARCnet formal, which made part of the ANSI 878.1 standard LAN. As supports a data transfer speed of 2.5 Mbps, ARCnet uses a bus logical topology and a slight variation of the physical topology of a star. Each network node is connected to a passive or an active hub. The NIC in each computer is connected to a cable which in turn is connected to an active or passive hub. ARCnet is based on a signal path scheme (token passing) to manage the flow of data between network nodes. When a node holds the token (signal), can transmit data over the network. All nodes, except the intended recipient, ignore the data. As it passes the token to each node, the node can send data. Since each node can send data only when it has the token in ARCnet collisions do not happen that often occur in a scheme such as CSMA / CD. Therefore, ARCnet is less susceptible to saturation of the Ethernet network. For a while ARCnet was the most popular LAN standard, but due in part to its relatively low speed (2.5 Mbps compared to 10 Mbps Ethernet), rarely used for new installations. Ethernet Ethernet networks, which is also known as IEEE 802.3, is the most popular standard for LANs that currently use. The 802.3 standard uses a bus logical topology and physical topology of a star or bus. Allows Ethernet data through the network at a speed of 10 Mbps Ethernet uses a data transmission method known as Multiple Access with Carrier Detection and Collision Detection (CSMA / CD). Before a node sends any data via an Ethernet network first listens and realizes if another node is transferring information. Otherwise, the node transfers the information through the network. All other nodes listen to the selected node and receive the information. If two nodes try to send data over the network at the same time, each node will notice the collision and wait a random amount of time before returning to ship.
The logical topology Ethernet bus allows each node takes turns in transmitting information across the network. Thus, the failure of a single node failure does not cause the entire network. Although CSMA / CD is a quick and efficient way to transmit data, a heavily loaded network could reach saturation point. However, with a properly designed network, saturation is rarely worrisome. There are three standard Ethernet, 10BASE5, 10BASE2, and 10BASE-T, which define the type of network cable length specifications and the physical topology to be used to connect nodes in the network. Token Ring Token Ring, also known as IEEE 802.5, was developed by IBM and some other manufacturers. With operation at a speed of 4 Mbps or 16 Mbps Token Ring uses a logical ring topology and a star physical topology. The NIC for each computer connected to a cable which, in turn, plugs into a central hub called a multistation access unit (MAU). Token Ring is based on a signal step scheme (token passing), ie passing a token (or signal) to all computers on the network. The computer is in possession of the token is authorized to transmit information to another computer on the network. When finished, the token is passed to the next computer in the ring. If the next computer has to send information, accepts the token and proceeds to send it. Otherwise, the token is passed to the next computer on the ring and the process continues. The MAU automatically bypasses network node that is not lit. However, since each node in a Token Ring network and then examines each token broadcast (signal), a node can malfunction to stop work across the network. Token Ring tends to be less efficient than CSMA / CD (Ethernet) networks with low activity, it requires additional overhead. However, with increasing network activity, Token Ring becomes more efficient than CSMA / CD. Several new technologies new technologies that meet the needs of today's networks, including Fast Ethernet, FDDI, Frame Relay and ATM. Fast Ethernet, also called 100BASEX, is an extension of the Ethernet standard that operates at speeds of 100 Mbps, up to 10 times greater than the standard 10 Mbps Ethernet interface for data distribution optical fiber (FDDI) is a standard for data transfer by fiber optic cable.
The ANSI standard for FDDI X3T9.5 specifies a rate of 100 Mbps Since the fiber optic cable is not susceptible to electrical interference or as susceptible to the degradation of the network signal as with standard network cable, FDDI allows the use of much longer cable than other network standards. The Frame Relay (Frame Relay) is a connection-oriented service to move data from one node to another at a reasonable speed and low cost. The frame relay can be seen as a virtual leased line. The user rents a permanent virtual circuit between two points and then you can send frames or frames (ie, packages) up to 1600 bytes between them. Besides competing with leased lines, frame relay competes with X.25 permanent virtual circuits. ATM means Asynchronous Transfer Mode, is a set of international standards for data transfer, voice and video through a network at very high speeds. Since it operates at speeds ranging from 1.5 Mbps to 1.5 Gbps, ATM incorporates standards of Ethernet, Token Ring and FDDI for data transfer. Back to topics in this section Description of the OSI model The OSI reference model is the current network architecture more prominent. The aim of this is to develop standards for open systems interconnection (Open System Interconnection, OSI). The term OSI is the name given to a set of standards for communication between computers, terminals and networks. OSI 7-layer model, where each layer defines the procedures and rules (standard protocols) that communications subsystems must follow in order to communicate with their corresponding processes of the other systems.
This allows a process running on a computer, can communicate with a similar process on another computer, if they implement the same communication protocols OSI layers. Some of the functions of each layer or level are described below: Level of Implementation. It defines a number of applications for communication between different systems, which manage: File Transfer (FTP). Exchange of messages (email). Presentation level. This layer performs the following functions: It formats the information to view or print. Interpreting the codes that are in the data (code conversion). It manages data encryption. It performs the data compression. Level of Session. Provides mechanisms for organizing and structuring dialogues between application processes. It acts as a moderating element can coordinate and control the exchange of data.
