OSI is known as Open Systems Interconnection, it's built from seven part layers. In this seven layers, they have the similar function for each layer. These seven layer are link to each other's. Every layer are providing error free though every layer and the lower layer provide send and receive data. Every layer also known as an N, and N is the entity request for N+1. The seven layers are: "Physical layer, Data layer, Touch layer, Transport layer, Session Layer, Presentation layer and Application layer. The most usually used network protocols are TCP/IP.
Physical Layer defines as the electrical and physical specifications for devices. Generally, he defines a relationship between a device and a transmission medium, such as a copper or optical cable. The function of physical is for built and termination of a connection to a communications, participants to the process to get more resources for share among the clients, modulation between user's digital equipment and across the message of signals. These signals operating over the physical cabling or over a radio link. In the physical layer, it's including two types of data transmitted that are analog data and digital data. Analog data is produced by telephones and sound waves, which vary continuously over time, analogous to one's voice. Analog data can take on any value in a wide range of possibilities. Digital data are produced by computer which is in the binary form. The digital data are represented as code in a series of ones and zeros. For example of digital data :" 1010111", all digital data is either on or off, 0 or 1. 1 equals to on, and 0 equals to off.
Analog and digital data can be processed by two ways that are analog transmission and digital transmission. The between of analog transmission and digital transmission in analog data are, in the analog transmission, analog is only for AM, FM radio, and broadcast TV compare to digital transmission, analog data is go though to pulse code modulation, MP3, CDs, iPOD, cellphones, and so on. The between of analog transmission and digital transmission on digital data, for example: "dial up modem sending email from your house, and Codes such as ASCII or EBCDIC run over Ethernet LANS." There has several of process that signaling, that are:" unipolar signaling, bipolar signaling, Manchester encoding. Signal of bits, digital transmission are signals sent as a series of "square waves" of either positive or negative voltage. Voltages vary between +3/-3 and +24/-24 depending on the circuit.
Data Link layer
The data link layer provides the functional and procedural means to transfer data between the network and data link layer can be detect as possible and correct the errors that may occur in the first layer which are physical layer. Usually this layer is for point to point and point to multipoint media in the wide area media in the telephone system. Data link layer are responsible for moving messages from one device to another device to controls the way messages are sent on media. There are 3 functions of data link layer protocol : "Media access control, Error control and message delineation."
Media Access Control (MAC) is generally control computer when computer make a transmission, MAC are shared circuit with point to point half duplex, and multipoint configurations. Error Control provides correct the transmit error when the error is detected. Error control will detected two error, that is network error and human errors. Message Delineation is for identifying the end and first of a message.
Network Layer
Network layer are responsible for addressing and routing of messages, it will automatically selects the best from computer to computer until the message had reached the end. it must be done through a number of data links that may can go for more communication subnet. Beside that's, network layer are also performs encapsulation on sending end, performs decapsulation on receive end. In the part of sending end, it will adds network layer header to message segments and receiving end will remove the header and pass them to the transport layer.
Transport Layer
In the computer network, transport layer provide end to end communication service for protocols and components. Transport layer provides connection data, reliability, multiplexing, stream support and multiplexing. This layer is including TCP/IP model. The very famous transport protocol are transmission control protocol. Transmission control protocol are links the application layer to the network layer. Transport layer responsible for segmentation and reassembly for breaking the message into several smaller pieces at the terminated.
Session Layer
This layer can also be referred to as a dialogue meeting between layer or layers, in the session layer and above. Session layer provides for opening, closing and run a session of end use process. Session layer are consists request respond and happen between an application, and service are usual use in application environments that use remote procedure calls. For example session layer protocol is OSI protocol suite, aka X.225. If the connection loss this packet may recovery the loss connection. If the connection is not use for long time, it will auto closed and re open it. This will provide half or full duplex operation.
Presentation Layer
The purpose of this layer is solving the problem syntax supported by information. It will exchange data from a user for the syntax. Data compression and decompression, encryption and decryption work by the presentation layer is responsible for. Layer applications and networks, as translation officer, at the presentation layer, the data network can be understood in accordance with the program format; This format is also a result of the type used by the network varies. Layer of management data decryption and encryption, such as the system password in the Internet, check processing, if your bank account, using a secure connection that is. Your account data is encrypted before it is sent in the network the other side of that layer will be received decrypt the data. In addition, the presentation layer protocol is also information on the image and file formats to decode and encode.
Communication between the application layer to determine the nature of the process in order to meet user needs as well as providing network and user application software interface between the services. It provides access to network for end-user and the user's capabilities are solely determined by the items that are available on this layer. Logic needed to support various applications. This means that there is a need for a processor that is capable of completing the commands given. Each type of application (file, transfer, remote access) requires different software to function on this layer. The application layer of the OSI layer closest to end users, which means that between the OSI application layer and user application software, through direct interaction. Note that the application layer is not by the computer software running on the practical application of the composition, but by the applications to access network resources of the API (Application Program Interface, application program interface), with this type of application software programs beyond the scope of the OSI model. Application layer functions typically include identification communication partners, the definition of resource availability and synchronous communication. Because it might lose communication partner, the application layer data transfer applications must be routines for the definition of communication partner identification and availability. The definition of resource availability, the application layer in order to communicate the request must determine whether there are sufficient network resources. In synchronous communication, all communication between applications requires the application layer coordination.
CONCLUSION FOR QUESTIOn 1
One of the needs most pressing communications system is the establishment of standards, no they could only communicate with each other teams from the same manufacturer and to use the same technology. The connection between electronic devices has been gradually standardized, the OSI model is the main reference for network communications. Although other models , at present most net makers link their products to the OSI model, especially when they want to teach users how to use their products.
The manufacturers consider it the best tool available to teach how to send and receive data over a network .The OSI reference model allows users to view network functions that occur in each layer. It is a model understandable for users.
Also at work was defined and explained in both IP version 4 as the new version, IP version 6. Understanding that need the creation of the new version is in the depletion of IP addresses above. OSI model was explained and emphasis was placed on layer 3, because in this layer works or operates the Internet Protocol, ie IP protocol, in this layer provides communication and determines the way to take the data in the network.
The topology or logic of a network is defined as how to lay the cable stations working individual, for walls, floors and ceilings of the building. There are number of factors to consider when determining which topology is most appropriate for a given situation. The topology in a network is the configuration adopted by the workstations to connect to each other. Topology can be known as a virtual shape or a organization of network. This shape was not corresponding of the physical design in computer network. In the computer home network can be arrange to a circle shape but it doesn't mean it is ring topology. Any specific network topology can be decided between physical or logic graphical mapping point.
In the local area network (LAN), each machine will connect only one cable. Every computer or server will connect to single bus cable though router. To prevent the signal from rolling back on the bus topology, on the each end of the bus topology will need a terminator. A signal is connect transfer in both directions to all computer or server with bus cable until found the MAC address or IP address. If machines could not found the same address for the intended data, the data will be ignoring by the machines. Although bus topology has only one wires, but its inexpensive than other topology. There are two type of connection in bus topology. That are linear bus and distributed bus. In the linear bus the type of network topology are connected to a common transmission medium which has two endpoints. Bus topology is commonly represent as backbone and trunk. All the data is transmission in the network is transmitted over this common transmission and is able to receive all the nodes. The two end point of commonly transmission and device are called as terminator, this is show impedance of the transmission are dissipates or absorbs the energy in the signal is still prevent reflected or impedance of transmission will be reflected the opposite of signal, this happen will cause signal of impedance transmission will be interference and degradation. In the distributed bus, the type of network topology is connected to a common transmission medium which has more than two endpoints that are built branches to the transmission main part. The physical distributed bus are almost same function as the physical liner bus topology.
In the local are network with a star topology, star topology is connected all to a centre point. Compare to the bus topology, star topology connected to all nodes with point to point connection. All traffic networks are passed with center hub. The hub act as a signal booster or repeater. Star topology is also known as a very simple network topology to the implement and design of all the network topology. The advantages of star topology are can be add additional nodes. The disadvantages of star topology are the hub represents the single point of failure. For an example, if the hub got problem the other network will not working as well, because the hub is the main session. A point to point connection sometimes will catagoly as a special physical star topology, therefore the most simple type is built at physical star topology, including point to point to a second node, the choice of node are "hub" and "spoke". Start topology are describe as either multi-access broadcast or non broadcast multi access, its depending on network or auto transmission a signal at the hub to all spokes or any address individual spokes with each communication. There a two type of network topology in star topology which is extended star and distributed star. Extended star has one or more repeaters between the central node and the spoke node, the repeater being used to extend the maximum transmission distance of the point to point links between the central and peripheral nodes. If the repeater are based on physical extended star topology are represent with hubs or switcs, then a hybrid network topology is built that is referred to hierarchical star topology. Distributed star are connect together in a linear with no central and up level point.
Tree topology is connect to others node that are one level lower in the hierarchy with point to point link between each of the second level node and the top level central root node. Each of the second level of nodes are connected to the higest main node will have one or more other nodes that are one level beneth them connected to it with a point-to-point link.The top main 'root' node is the only node that has no other node above it in the hierarchy. In the network, every nodes having it specific number, connected to a lower level in hierarchy, the number of nodes referred to "branching factor" of the hierarchical tree. This tree has individual nodes. A network based on physical hierarchical topology must have at least three levels in the hierarchy of the tree, because a central root node and the only one hierarchical level below it would exhibit the physical topology of a star. The one would be classified as a physical linear topology is based upon physical hierarchical topology and branching factor. The branching factor is independent of number of nodes in the network. The point to point physical hierarchical topology will be one or less than the total number of nodes in the network. If the nodes are based upon the physical hierarchical topology are required to any process upon the data that is transmission between nodes in the network, the nodes are in high level will be process more than the lower nodes, such this topology is very useful and high recommend.
A ring topology is a network topology or circuit of network, in which network every network device is attached along the same signal to the other two devices, then it will forming a ring path. Through the ring, every device in the network is referred to as nodes in every message. Each of the node having their unique address. Since in a ring topology only have two node on the pathway, ring topology are generally disrupted by the failure of a single link. The redundant topology is use for eliminate network server down caused by a single point failure. All network need redundancy for enhanced reliability. Network reliability is though devices and network design that are tolerant to faults or failures. Fiber distributed data interface (FDDI) networks overcome when network sending data on a counterclockwise and clockwise ring. If a data is wrapped when processing, the data will back to complementary ring before it reaches the end. The most use in ring topology are token ring. ADVANTAGES and DISadvantages of RING TOPOLOGY A ring is relatively easy to install and reconfigure. Each device is linked only to its immediate neighbors (either physical or logical). To add or remove devices, you just have to move two connections. The only restrictions are related to aspects of the physical environment and traffic (maximum length of the ring and number of devices). In addition, failures can be isolated easily. Generally, a ring signal is a continuous movement.
CONCLUSION FOR QUESTION 2
Ultimately, there are a number of factors that are needed to be taken into account when deciding on a particular network topology. Among them are the distribution of the equipment to connect. This must be done according to the arrangement of the hardware. The types of applications that need to be run and accesed also play a part on the topology used in the organization. The cost you want to devote to maintaining and upgrading the local network is also a factor that depends on the implementation of the new topology. Lastly, the traffic flowing through the network chosen should be less than the limit of the topology used.
