Contents1.Introduction2.Basic types of topologies3.Classification of network topologies 3.1 Physical topologies 3.1.1 Classification of physical topologies 126.96.36.199 Point-to-point 188.8.131.52 Bus 184.108.40.206 Star 220.127.116.11 Ring 18.104.22.168 Mesh 22.214.171.124 Tree 3.1.2 Hybrid network topologies 3.2 Signal topology 3.3 Logical topology4.References
An Introduction toNetworking topologyNetwork topology is the study of the arrangement or mapping of the elements (links,nodes, etc.) of a network, especially the physical (real) and logical (virtual)interconnections between nodes A local area network (LAN) is one example of anetwork that exhibits both a physical topology and a logical topology. Any given nodein the LAN will have one or more links to one or more other nodes in the network andthe mapping of these links and nodes onto a graph results in a geometrical shape thatdetermines the physical topology of the network. Likewise, the mapping of the flow ofdata between the nodes in the network determines the logical topology of the network.It is important to note that the physical and logical topologies might be identical in anyparticular network but they also may be different.Any particular network topology is determined only by the graphical mapping of theconfiguration of physical and/or logical connections between nodes. LAN NetworkTopology is, therefore, technically a part of graph theory.
Basic types of topologiesThe arrangement or mapping of the elements of a network gives rise to certain basictopologies which may then be combined to form more complex topologies (hybridtopologies). The most common of these basic types of topologies are :Bus -Linear -Linear BusStarRingMesh -partially connected mesh (or simply mesh) -fully connected meshTreeHybridPoint to Point
Classification of network topologiesThere are also three basic categories of network topologies:physical topologiessignal topologieslogical topologiesThe terms signal topology and logical topology are often used interchangeably eventhough there is a subtle difference between the two and the distinction is not oftenmade between the two.
Physical topologiesThe mapping of the nodes of a network and the physical connections between them –i.e., the layout of wiring, cables, the locations of nodes, and the interconnectionsbetween the nodes and the cabling or wiring systemIts classification is: 1.Point-to-point 2.Bus 3.Star 4.Ring 5.Mesh 6. Tree
Point-to-pointThe simplest topology is a permanent link between two endpoints. Switchedpoint-to-point topologies are the basic model of conventional telephony. The valueof a permanent point-to-point network is the value of guaranteed, or nearly so,communications between the two endpoints. The value of an on-demand point-to-point connection is proportional to the number of potential pairs of subscribers, andhas been expressed as Metcalfes Law.
Bus : 1.Linear busThe type of network topology in which all of the nodes of the network are connected toa common transmission medium which has exactly two endpoints (this is the bus,which is also commonly referred to as the backbone, or trunk) – all data that istransmitted between nodes in the network is transmitted over this common transmissionmedium and is able to be received by all nodes in the network virtually simultaneously(disregarding propagation delays).Note: The two endpoints of the common transmission medium are normallyterminated with a device called a terminator that exhibits the characteristicimpedance of the transmission medium and which dissipates or absorbs the energy thatremains in the signal to prevent the signal from being reflected or propagated back ontothe transmission medium in the opposite direction, which would cause interference withand degradation of the signals on the transmission medium (See Electrical termination).
2.Distributed busThe type of network topology in which all of the nodes of the network are connected toa common transmission medium which has more than two endpoints that are created byadding branches to the main section of the transmission medium – the physicaldistributed bus topology functions in exactly the same fashion as the physical linear bustopology (i.e., all nodes share a common transmission medium).Notes:1.) All of the endpoints of the common transmission medium are normally terminatedwith a device called a terminator (see the note under linear bus).2.) The physical linear bus topology is sometimes considered to be a special case of thephysical distributed bus topology – i.e., a distributed bus with no branching segments.3.) The physical distributed bus topology is sometimes incorrectly referred to as aphysical tree topology – however, although the physical distributed bus topologyresembles the physical tree topology, it differs from the physical tree topology in thatthere is no central node to which any other nodes are connected, since this hierarchicalfunctionality is replaced by the common bus.
StarThe type of network topology in which each of the nodes of the network is connected to a central node with a point-to-point link in a hub and spoke fashion, the central node being the hub and the nodes that are attached to the central node being the spokes (e.g., a collection of point-to-point links from the peripheral nodes thatconverge at a central node) – all data that is transmitted between nodes in the network is transmitted to this central node, which is usually some type of device that then retransmits the data to some or all of the other nodes in the network, although thecentral node may also be a simple common connection point (such as a punch-down block) without any active device to repeat the signals.
RingThe type of network topology in which each of the nodes of the network is connected totwo other nodes in the network and with the first and last nodes being connected toeach other, forming a ring – all data that is transmitted between nodes in the networktravels from one node to the next node in a circular manner and the data generally flowsin a single direction only. Dual-ringThe type of network topology in which each of the nodes of the network is connected totwo other nodes in the network, with two connections to each of these nodes, and withthe first and last nodes being connected to each other with two connections, forming adouble ring – the data flows in opposite directions around the two rings, although,generally, only one of the rings carries data during normal operation, and the two ringsare independent unless there is a failure or break in one of the rings, at which time thetwo rings are joined (by the stations on either side of the fault) to enable the flow ofdata to continue using a segment of the second ring to bypass the fault in the primaryring.
MeshThe value of fully meshed networks is proportional to the exponent of the number ofsubscribers, assuming that communicating groups of any two endpoints, up to andincluding all the endpoints, is approximated by Reeds Law. Fully connectedThe type of network topology in which each of the nodes of the network is connected toeach of the other nodes in the network with a point-to-point link – this makes it possiblefor data to be simultaneously transmitted from any single node to all of the other nodes. Partially connectedThe type of network topology in which some of the nodes of the network are connectedto more than one other node in the network with a point-to-point link – this makes itpossible to take advantage of some of the redundancy that is provided by a physicalfully connected mesh topology without the expense and complexity required for aconnection between every node in the network.
TreeAlso known as a hierarchical network.The type of network topology in which a central root node (the top level of thehierarchy) is connected to one or more other nodes that are one level lower in thehierarchy (i.e., the second level) with a point-to-point link between each of the secondlevel nodes and the top level central root node, while each of the second level nodesthat are connected to the top level central root node will also have one or more othernodes that are one level lower in the hierarchy (i.e., the third level) connected to it, alsowith a point-to-point link, the top level central root node being the only node that hasno other node above it in the hierarchy – the hierarchy of the tree is symmetrical, eachnode in the network having a specific fixed number, f, of nodes connected to it at thenext lower level in the hierarchy, the number, f, being referred to as the branchingfactor of the hierarchical tree.
Hybrid network topologiesThe hybrid topology is a type of network topology that is composed of one or moreinterconnections of two or more networks that are based upon different physicaltopologies or a type of network topology that is composed of one or moreinterconnections of two or more networks that are based upon the same physicaltopology, but where the physical topology of the network resulting from such aninterconnection does not meet the definition of the original physical topology of theinterconnected networks (e.g., the physical topology of a network that would resultfrom an interconnection of two or more networks that are based upon the physical startopology might create a hybrid topology which resembles a mixture of the physical starand physical bus topologies or a mixture of the physical star and the physical treetopologies, depending upon how the individual networks are interconnected, while thephysical topology of a network that would result from an interconnection of two ormore networks that are based upon the physical distributed bus network retains thetopology of a physical distributed bus network).
Signal topologyThe mapping of the actual connections between the nodes of a network, as evidencedby the path that the signals take when propagating between the nodes.Note: The term signal topology is often used synonymously with the term logicaltopology, however, some confusion may result from this practice in certain situationssince, by definition, the term logical topology refers to the apparent path that the datatakes between nodes in a network while the term signal topology generally refers to theactual path that the signals (e.g., optical, electrical, electromagnetic, etc.) take whenpropagating between nodes.Example:In an 802.4 Token Bus network, the physical topology may be a physical bus, aphysical star, or a hybrid physical topology, while the signal topology is a bus (i.e., theelectrical signal propagates to all nodes simultaneously [ignoring propagation delaysand network latency] ), and the logical topology is a ring (i.e., the data flows from onenode to the next in a circular manner according to the protocol).
Logical topologyThe mapping of the apparent connections between the nodes of a network, as evidencedby the path that data appears to take when traveling between the nodes.Classification of logical topologiesThe logical classification of network topologies generally follows the sameclassifications as those in the physical classifications of network topologies, the paththat the data takes between nodes being used to determine the topology as opposed tothe actual physical connections being used to determine the topology.
ReferencesGoogle.comWikipedia.comComputeronline.comNetworking topologies-E.BalguruswamyA Text book of computers-Andrew SymondsA first cource in computers-Sanjay Saxena