An Introduction To Network Topology

An Introduction To interlock TopologyIn the context of a talk ope direct on, the term topology refers to that way in which the end points, or brands, attached to the workwork are unite or it is the arrangements of clays in a computer ne 2rk. It ass be either sensible or logical. The corporal topology refers that, a way in which a network is laid out physic al unrivaledy and it leave al nonpareil include the devices, installation and location. Logical topology refers that how a information transfers in a network as opposed to its design.The network topology deal be categorized into manager, call, star, tree diagram and mesh. loanblend networks (They are the conglomerate networks, which can be built of two or more topologies). mound TopologyA flock topology is char moveerized by the use of a multi point forte. A considerable and single cable acts as a backbone to connect all the devices in a network. In a spate topology, all computers or stations attach by din t of the appropriate ironware interfacing known as a tap, nowadays to a cumulus network. Full semidetached house operation among the station and tap allows entropy to enthrall onto the bus and received from the bus. A transmitting from any station propagates the duration of the medium in both directions and can be received by all separate stations. At severally end of the bus is a terminator, which absorbs any signal, removing it from the bus. Nodes are attached to the bus cable by mow lines and taps. A drop line is a confederacy running amid the device and the main cable. A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core. A bus network work best with a limited issuance of computers.AdvantagesBus topology can install very easily on a network.Cabling get out be less compare to other topologies because of the main backbone cable laid efficiently in the network path.Bus topology suited for a small network.If one computer fails in the network, the other computers are not affected they ordain continue to work.It is alike less high-priced than star topology.DisadvantagesThe cable length will limited and there by limits the fall of stations.If the backbone cable fails, the built-in network will goes down.It is very difficult to trouble shoot.Maintenance cost is very high in a long run.Terminators are required for both the ends of the cable.Ring topologyThe ring topology the network consists of use point to point connection and a set of repeaters in a closed loop. A signal is passed along the ring in one direction, from device to device, until it r apiecees its destination. It may be clock wise or anti clock wise. When a device receives a signal intend for another device, its repeater generates the opuss and passes them along. As with the bus and tree, data are transmitted in way outs. As a frame circulates past all the other stations, the destination s tation get it on its forebode and copies the frame into a local buffer as it goes by. The frame continues to circulate until it re bendings to the source station, where it is removed. These topologies are used in school campuses and some office buildings.tifsTemp 13.a.tifFigure (2) Bus topologyAdvantagesIt per sortings better than star topology under heavy work loadFor managing the connection between the computers, there is no collect for the network server.It is cheaper than star topology because of less wiring.By adding the token ring in the network, can create large network.Very order network because all the devices has a vex to the token ring and opportunity to transmit.DisadvantagesA break in the ring (such as a disable station) can disable the total network.It is much slower than an Ethernet network with under normal load.Any moves, changes and adds of the devices can affect the network. interlocking connection devices like (Network adapter cards and MAU) are much more set down than Ethernet cards.Star TopologyIn a star topology, each station is directly attached to a common node called hub. Unlike a mesh technology, the devices are not directly affaireed to one another. A star topology does not allow direct traffic between devices. The look intoler act as an exchange, like if one device wants to send to another, it sends the data to the controller, which then relays the data to the connected device. In a star, each device needs only one link and one I/O port to connect it to any number of others. The star topology is used in local empyrean networks (LAN) and sometimes high speed LAN often uses a star topology with central hub.AdvantagesIf one link fails in the star topology, only that link is affected. All other link remain active.It is flourishing to identify the fault and fault isolation.Easy to expand the network in the star topology.No disruptions to the network when connecting or removing devices.It is very easy to manage because of i ts simplicity in the function.DisadvantagesIn a star topology, if the hub goes down, the entire network will fails.It requires more cable length compared to the linear bus topology.It is much more pricey than bus topology, because of the cost of the hubs.Tree TopologyA tree topology is the generalization of the bus topology. It integrates the nine-fold star topologies unitedly on to a bus. The transmission medium is a offseting cable with no closed loops. The tree layout begins at a point known as the head end. The branches in turn may hold in additional branches to allow quite complex layouts. A transmission from any station propagates throughout the medium and can be received by all other stations. This topology will allow for the expansion of an existing network.AdvantagesTree topology is well supported by the computer hardware and parcel vendors.Point to point wiring for each and every segments of the network.It is the best topology for the branched networks.DisadvantagesI t is more expensive because more hubs are required to install the network.Tree topology is entirely depends upon the backbone line, if it fails then the entire network would fail.It is very difficult to configure and wire than other network topologies.In a tree topology, the length of network depends on the type of cable being used.Mesh TopologyIn a mesh topology, every device has a dedicated point-to-point link to every other device. The term dedicated means that the link carries traffic only between the two devices it connects. To find the number of physical golf links in a amplyy connected mesh network with n nodes, we scratch consider that each node must be connected to other node. Node 1 must be connected to n-1nodes, node 2 must be connected to n-1nodes, and finally node n must be connected n-1 nodes. However, if each physical link allows communication in both directions, we can divide the number of links by 2.In other words we can say that in a mesh topology, we need n (n-1 )/2.tifsTmp9.tifFigure (5 Mesh topologySuppose if we are connecting 15 nodes in a mesh topology, then the number of cables requiredDA = n (n-1)/2 DA = Number of cables= 15 (15 1)/2 n = Node= 15*14/2= 15*7= 105Therefore, the total number of cables required for connecting 15 nodes = 105.AdvantagesThere is no traffic problem because of the dedicated link in the mesh network.Mesh topology is robust. If one link becomes unusable. It does not incapacitate the entire dust.Point-to-point links make full identification and fault isolation easy.Security or privacy for data travels along the dedicated line.Network can be expanded without any disruptions to the exploiters.DisadvantagesInstallation and reconnection are difficult.Large amount of cabling and the number of I/O ports requiredSheer bulk of the wiring can be greater than the available home can accommodate.The hardware required to connect each link can be prohibitively expensive.Hybrid TopologyA network can be hybrid, which uses t wo or more network topologies together in a network. For example, we can pick out a main star topology with each branch connecting several stations in a bus topology.The OSI ModelThe Open System Inter connection (OSI) reference puzzle was developed by the International Organization for Standardization (ISO)2 as a model for a computer protocol computer architecture and as a frame work for developing protocol standards. The purpose of the OSI model is show how to facilitate communication between different systems without requiring changes to the logic of the underlying hardware and software. The OSI model is not a protocol it is a model for understanding a network architecture that is flexible, robust and interoperable. The OSI model is a stageed frame work for the design of network systems that allows communication between all types of computer systems. It consists of seven separate but related grades, each of which defines a part of the butt on moving information crossways a network.The seven tiers of the OSI reference model can be shared into two categories upper works and lower seams.Upper Layers of the OSI Models areApplication horizontal surfacePresentation spirit level session spirit levelThe upper layers of the OSI model designate the covering issues, presentation session stages and generally are utilize only in software. The highest layer, (the drill layer) is close to the end exploiter. These upper layers are act as an porthole between the user and the computer. The term upper layer is sometimes used to refer to any layer above another layer in the OSI model.Examples of upper layer technologies in the OSI model are SNMP, FTP, and web etc.Lower Layers of the OSI ModelTransport layerNetwork layer data link layer bodily layerThe lower layers of the OSI model provide network specific functions like data expect issues (flow control, addressing and routing). The lower layers of the OSI model (the physical layer and the data link layer) a re implemented in hardware and software as well. Examples of lower layer technologies in the OSI model are TCP, UDP, IP, IPX etc.Application layerThe application layer enables the user, whether human or software, to access the network. It provides user interfaces and support for function such as electronic mail, removed file access and transfer, shared database management, and other types of distributed information services. The application layer provides specific services like network virtual oddment, file transfer, access and management, mail services and directory services.Network virtual terminal A network virtual terminal is a software version of physical terminal, and it allows a user to log on to a remote host.File transfer, access and management This application allows a user to access files in a remote host (to make changes, read data), to retrieve files from a remote computer for use in the local computer and to manage or control files in a remote computer locally.Mail services The application provides the basis for e-mail forwarding and storage.Directory services This application provides distributed database source and access for global information about various objects and services.Presentation layerThe presentation layer is concerned with the syntax and semantics of the information exchanged between two systems. The presentation layer is responsible for the translation, capsule and encryption. Messages are sending between the layers.Translation The accomplish in two systems are usually exchanging in the form of character strings, numbers, and so on. The information is changed into bit electric currents before being transmitted. The presentation layer at the sender changes the information from its sender dependent format into a common format. On the receiving machine, the presentation layer changes the common format into its receiver-dependent format.Encryption Encryption means that the sender transforms the fender information to another f orm and sends the resulting content out over the network. Decryption reverses the original cognitive process to transform message back to its original form.Compression Data compression reduces the number of bits contained in the information. It becomes particularly important in the transmission of multimedia system such as text, audio and video.Session layerThe session layer is the network dialog controller. It establishes, maintains and synchronizes the fundamental interaction among communicating systems. These layers have specific responsibilities include the followingDialog control The session layer allows two systems to enter into a dialog. It allows the communication between twp processes to take place in either half duplex (one way at a time) or full duplex (two ways at a time) mode. synchronization The session layer allows a process to add check points, or synchronization points, to a pelt of data.Examples for session layers are MPEG, JPEG, MIDI, NCP etc.Transport layerThe go layer is responsible for process to process delivery of the entire message. The transport layer is responsible for the delivery of a message from one process to another. A process is an application program running on a host. The transport layer ensures that the full message arrives intact and in order, overseeing both error control and flow control at the source-to-destination level. It also has some specific responsibilities mentioned belowService-point addressing The transport layer includes a type of address called a service-point address (or port address). The network layer gets each packet to the correct computer, the transport layer gets the entire message to the correct process on that computer.Segmentation and reassembly A message is divided into transmittable segments, with each segment containing a sequence number. These numbers enable the transport layers to reassemble the message correctly upon arriving at the destination and to identify and replace packets that we re lost in transmission.Connection control The transport layer can be either connectionless or connection oriented. A connectionless transport layer treats each segment as an independent packet and delivers it to the transport layer at the destination machine. If a connection oriented transport layer make a connection with the transport layer at the destination machine first before delivering the packets. After all the data are transferred the connection is terminated.Flow control The transport layer is responsible for the flow control. However, flow control at this layer is performed end to end rather than across a single link. faulting control Transport layer is also responsible for the error control. Error control at this layer is performed process-to-process rather than across a single link. The sending transport layer makes sure that the entire message arrives at the receiving transport layer without error.These layers using the TCP/IP and UDP protocols.Network layerThe networ k layer is responsible for the source to destination delivery of a packet, possibly across multiple networks (links). This layer ensures that each packet gets from its point of origin to its final destination. Network layers also have other responsibilities include the followingLogical addressing If a packet passes the network boundary, it needs another addressing system to help distinguish the source and destination systems. The network layer adds a header to the packet advance from the upper layer that, among other things, includes the logical addresses of the sender and receiver.Routing When independent networks are connected to create internetworks or a large network, the connecting devices route or switch the packets to their final destination.Data link layerThe data link transforms the physical layer, a raw transmission facility, to a reliable link. It makes the physical layer get on error-free to the upper layer. It also has other responsibilities include the followingFrami ng The data link layer divides the flow of bits received from the network layer into manageable data units called frames.Physical addressing The data link layer adds a header to the frame to define the sender and/or receive of the frame. If the frame is intend for a system outside the senders network, the receiver address is the address of the device that connects the network to the next one.Flow control If the rate at which the data are absorbed by receiver is less than the rate at which data are produced in the sender, the data link layer impose a flow control mechanism to avoid overwhelming the receiver.Error control The data link layer adds reliability to the physical layer by adding mechanisms to detect and retransmit damaged or lost frames. It also uses a mechanism to recognize duplicate frames. Error control is normally achieved through a trailer added to the end of the frame.Access control When two or more devices are connected to the same link, data link layer protocols a re necessary to determine which device has control over the link at any given time.Data link contains two sub layers LLC (Logical Link Control) and MAC (Medium Access Control).LLC is the upper sub layer, which maintains and establishes the communication links to the device. And it also responsible for the frame error control and addressing.MAC is the lower sub layer of the data link layer. It controls how the devices sharing the media channel.Physical layerThe physical layer coordinates the functions required to carry a bit stream over a physical medium. It deals with the mechanical and electrical specifications of the interface and transmission medium. It also defines the procedures and functions that physical devices and interfaces have to perform for transmission to occur.The physical layer is also concerned with the followingPhysical characteristics of interface and medium Physical layer defines the characteristics of the interface between the devices and the transmission medium . It also defines the type of transmission medium.Representation of bits This layer data consists of a stream of bits with no interpretation. To be transmitted, bits must be encoded into signals electrical or optical. The physical layer defines the type of encoding.Data rate The transmission rate the number of bits sent each second- is also defined by physical layer. In other words physical layer defines the duration of a bit, which how long it lasts.Synchronization of bits The sender and receiver not only must use the same bit rate but also must be synchronized at the bit level.Line constellation The physical layer is concerned with the connection of devices to the media. In a point-to-point configuration, two devices are connected through a dedicated link. In a multipoint configuration a link is shared among several devices.Physical topology The physical topology defines how devices are connected to make a network. Devices can be connected by using a mesh topology, a star topolog y, a ring topology, a bus topology, or a hybrid topology.Transmission mode The physical layer also defines the direction of transmission between two devices simplex, half duplex, or full duplex.