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									                                          Topology
    The physical topology of a network refers to the configuration of cables, computers, and
    other peripherals. Physical topology should not be confused with logical topology which
    is the method used to pass information between workstations.

    A network topology is the pattern of links connecting pairs of nodes of a network. A given node
    has one or more links butt to others, and the links can appear in a variety of different shapes. The
    simplest connection is a one-way link between two devices. A second return link can be added
    for two-way communication. Modern communications cables usually include more than one wire
    in order to facilitate this, although very simple bus-based networks have two-way
    communication on a single wire.

    Network topology is determined only by the configuration of connections between nodes; it is
    therefore a part of graph theory. Distances between nodes, physical interconnections,
    transmission rates, and/or signal types are not a matter of network topology, although they may
    be affected by it in an actual physical network.




                     Main Types of Physical Topologies
    The following sections discuss the physical topologies used in networks and other related
    topics.

   Mesh
   Star
   Tree
   Linear Bus
   Ring

                                     Mesh Topology
    A Mesh topology consists of a network where every device on the network is physically
    connected to every other device on the network. This provides a great deal of performance and
    reliability, however the complexity and difficulty of creating one increases geometrically as the
    number of nodes on the network increases. For example, a three or four node mesh network is
    relatively easy to create, whereas it is impractical to set up a mesh network of 100 nodes -- the
    number of interconnections would be so ungainly and expensive that it would not be worth the
    effort. Mesh networks are not used much in local area networks (LANs) but are used in Wide
    Area Networks (WANs) where reliability is important and the number of sites being connected
    together is fairly small. Figure Five shows an example of a four-node Mesh network.

     Mesh networking is a way to route data, voice and instructions between nodes. It allows for
    continuous connections and reconfiguration around blocked paths by "hopping" from node to
    node until a connection can be established.
    Mesh networks are self-healing: the network can still operate even when a node breaks down or a
    connection goes bad. As a result, a very reliable network is formed. Applicable to wireless
    networks, wired networks, and software interaction.

    Advantages of a Mesh Topology

   Guarantees that each connection can carry its own data.
   Eliminates traffic problems.
   It’s a robust network.
   It has a very high privacy and security.

    Disadvantages of a Mesh Topology

   Huge amount of cable and I/O ports are required.
   Installation is difficult.
   Hardware required are very costly




                                      Star Topology
    A star topology is designed with each node (file server, workstations, and peripherals)
    connected directly to a central network hub or concentrator.

     Data on a star network passes through the hub or concentrator before continuing to its
    destination. The hub or concentrator manages and controls all functions of the network. It
    also acts as a repeater for the data flow. This configuration is common with twisted pair
    cable; however, it can also be used with coaxial cable or fiber optic cable.



    Advantages of a Star Topology

   Easy to install and wire.
   No disruptions to the network then connecting or removing devices.
   Easy to detect faults and to remove parts.
                                           Star topology

.

    Disadvantages of a Star Topology

   Requires more cable length than a linear topology.
   If the hub or concentrator fails, nodes attached are disabled.
   More expensive than linear bus topologies because of the cost of the concentrators.




                                     Tree Topology
    A tree topology combines characteristics of linear bus and star topologies. It consists of
    groups of star-configured workstations connected to a linear bus backbone cable. Tree
    topologies allow for the expansion of an existing network, and enable schools to
    configure a network to meet their needs.




                                           Tree topology
    Advantages of a Tree Topology

   Point-to-point wiring for individual segments.
   Supported by several hardware and software venders.

    Disadvantages of a Tree Topology

   Overall length of each segment is limited by the type of cabling used.
   If the backbone line breaks, the entire segment goes down.
   More difficult to configure and wire than other topologies.




                                        Linear Bus
    A linear bus topology consists of a main run of cable with a terminator at each end. All
    nodes (file server, workstations, and peripherals) are connected to the linear cable.
    Ethernet and LocalTalk networks use a linear bus topology.




                                         Linear Bus topology




    Advantages of a Linear Bus Topology

   Easy to connect a computer or peripheral to a linear bus.
   Requires less cable length than a star topology.



    Disadvantages of a Linear Bus Topology

   Entire network shuts down if there is a break in the main cable.
   Terminators are required at both ends of the backbone cable.
   Difficult to identify the problem if the entire network shuts down.
   Not meant to be used as a stand-alone solution in a large building.
                                          Ring Topology
    A ring network is a topology of computer networks where each user is connected to two
    other users, so as to create a ring. The most popular example is a token ring network.

    Ring networks tend to be inefficient when compared to client/server networks because
    data must travel through more points before reaching its destination. For example, if a
    given ring network has eight computers on it, to get from computer one to computer four,
    data must travel from computer one, through computers two and three, and to its
    destination at computer four. It could also go from computer one through eight, seven,
    six, and five until reaching four, but this method is slower because it travels through more
    computers.




                                               Ring Topology




    Advantages of a Ring Topology

   Growth of the system has minimal impact on performance
   All stations have equal access.
   Each node on the ring acts as a repeater, allowing ring networks to span greater distances
    than other physical topologies.
   Because data travels in one direction high speeds of transmission of data are possible
   When using a coaxial cable to create a ring network the service becomes much faster.

    Disadvantages of a Ring Topology

   Often the most expensive topology
   Failure of one computer may impact others

								
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