What is a web?
A web is a group of computing machines that are interconnected.
The simplest manner to link two computing machines is to put a communicating circuit board on each of them and run a wire overseas telegram between them. So one computing machine would compose the informations to its communicating ( or interface ) circuit board as if it were composing informations to a disc, a proctor or a pressman. The finish computing machine would read the received informations from its circuit board as if it were reading the information from a disc or a keyboard.
Types of Network
Local Area Network – Local area network:
LAN stands for Local Area Network. Alternatively of linking one computing machine straight to another, and so on in sequence, LAN interconnects many computing machines utilizing one piece of hardware ( normally the LAN overseas telegram, and sometimes types of webs use a particular intent computing machine called the hub. In add-on, each computing machine on the web needs a overseas telegram to link to it, and a circuit board ( called Network Interface Card or NIC. )
LANs are designed for usage over a short distance ( within an office suite, a floor, a whole edifice ) , but non across a metropolis or a province.
Wide Area Network – Wide area network:
In a LAN, all we have to make to link computing machines to the web is install web cards on them, and link them utilizing a overseas telegram wire to the web overseas telegram or hub of the LAN. As you know, a LAN merely interconnects computing machines that are located in one physical vicinity, a room, a floor or a edifice.
WAN, which stands for Wide Area Network, interconnects computing machines over long distances. WANs transmit informations back and Forth either over regular telephone lines utilizing modems, or much more normally, utilizing dedicated long distance lines that are leased by the Telephone companies. Dedicated means they do nil but transmit informations for that specific web.
The difference between WAN and LAN, is that the Wide Area Network utilizations dedicated computing machines at each terminal of the web that co-ordinate web traffic on the transmittal lines. The usage of these dedicated computing machines keeps the web running independently of any of the computing machines that use it.
Metropolitan Area Network – Man:
A metropolitan country web ( MAN ) is a web that connects two or more local country webs or campus country webs together but does non widen beyond the boundaries of the immediate town/city. Routers, switches and hubs are connected to make a metropolitan country web
This web portions the features of package broadcast medium webs.
A MAN is optimized for a big geographical country than LAN.
Purpose of OSI Reference theoretical account
The OSI mention theoretical account allows us to see the web maps that occur at each bed. The OSI mention theoretical account is a frame work where we can understand how information travels throughout a network.In add-on, OSI mention theoretical account can be used to visualise how information, information packages, travels from application plans ( illustration: wires, paperss, so on ) , through a web medium to other application plans that are located in another computing machine on a web, even if the transmitter and the receiving system have different types of web media.
In the OSI mention theoretical account, there are seven numbered beds. Each bed explains a peculiar web map. This separation of networking maps is called layering.
The Seven Layers of the OSI Reference Model
The procedure of traveling the information between computing machines is divided into seven smaller stairss in the OSI mention theoretical account. Each of the seven smaller jobs is represented by its ain bed in the theoretical account. The seven beds of the OSI mention theoretical account are:
- Layer 7: Application bed
- Layer 6: Presentation bed
- Layer 5: Session bed
- Layer 4: Conveyance bed
- Layer 3: Network bed
- Layer 2: Datas link bed
- Layer 1: Physical bed
In the OSI mention theoretical account, we can understand how information travels through a web and what devices operate at each bed as information travels through them. Each OSI bed has a set of maps that it must execute for informations to go from a beginning to a finish on a web.
Figure of OSI mention theoretical account from book
The Upper Layers
The three upper beds of the OSI mention theoretical account are referred to as the application beds. The upper beds of the OSI mention theoretical account trades with the user interface, informations data format and the application entree.
Layer 7: The Application Layer
The application bed is the OSI bed that is closer to the user. It provides web services, such as file entree and printing, to the user ‘s application. It differs from the other beds in that it does non supply services to any other OSI bed, but merely to the applications outside the OSI theoretical account. Examples of such applications are spreadsheet plans, word processing plans, and bank terminal plans. If we want to retrieve Layer 7 in few words merely think of browsers.
Layer 6: The Presentation Layer
The presentation bed ensures that the information that the application bed of one system sends out is clear by the application bed of another system. If necessary, the presentation bed translates between multiple informations formats by utilizing a common format. This bed is besides responsible for compaction and encoding. If we want to retrieve Layer 6 in few words merely think of common informations format.
Layer 5: The Session Layer
As its name implies that the session bed establishes, manages and terminates Sessionss between two pass oning hosts. The seven beds provide its services to the presentation bed. It besides synchronizes duologue between the two hosts presentation beds and manages their informations exchange. In add-on to session ordinance, the session bed offers commissariats for efficient informations transportation, category of service and exclusion coverage of session bed, presentation bed, and application bed jobs. If we want to retrieve Layer 5 in few words merely think of duologues and conversations.
The Lower beds
The four beds of the OSI mention theoretical account specify how information is transferred across a physical wire through internetworking devices, to the coveted terminal station, and eventually to the application. The lower beds control the physical bringing of the informations.
Layer 4: The Transport Layer
The conveyance bed sections informations from the directing hosts system and reassembles the information into a information watercourse on the receiving hosts system. The boundary between the conveyance bed and the session bed can be thought of as the boundary between application protocols and data-flow protocols. Whereas the application, presentation, and session beds are concerned with the application issues, the four beds are concerned with informations conveyance issues.Specifically, such issues as how dependable conveyance between two hosts is accomplished is the chief concern of the conveyance bed. If we want to retrieve Layer 4 in few words merely think of flow control and dependability.
Layer 3: The Network bed
The Network bed is a complex bed that provides connectivity and way choice between two hosts systems that might be located on geographically separated webs. If we want to retrieve Layer 3 in few words merely think of way choice, routing, and logical addressing.
Layer 2: The Data Link Layer
The information nexus bed provides the theodolite of informations across a physical nexus. Here the informations nexus bed is concerned with the physical addressing, web topology, and web media entree and mistake sensing. If we want to retrieve Layer 2 in few words merely think of frames and media entree control.
Layer 1: The Physical Layer
The physical bed defines the electrical, mechanical, procedural, and functional specifications for triping, keeping, and deactivating the physical nexus between terminal systems.Such features as electromotive force degrees, timing of electromotive force alterations, physical information rates, physical connections and other similar properties are defined by physical bed specifications. If we want to retrieve Layer 1 in few words merely think of signals and media.
First allow us cognize what is meant by Topology
Topology defines the construction of the web. The topology definition contains two parts: the physical topology, which is the existent layout of the wire ( media ) , and the logical topology, which defines how the media is accessed by the hosts.
The physical topologies that are used normally are bus, ring, star, extended star, hierarchal, and mesh.
Uses a singlebackbone section ( length of the overseas telegram ) to which all the hosts straight connect.
Connects one host to the following and the last host to the first. This creates a physical ring of overseas telegram.
Connects all to a cardinal point of concentration. This point is normally a hub or a switch.
Extended Star Topology:
Uses the star topology. It links single stars together by associating the hubs/switches.
Similar to an drawn-out star topology, but alternatively of associating the hubs/switches together, each secondary system is linked to a primary computing machine that controls the traffic on the topology.
Used when there can be perfectly no interruption in communicating – for eg. , the control systems of a atomic power works.