The Open System Interconnection (OSI) reference model is an industry-standard framework created and maintained aside the International Standardization Governance (ISO). The OSI model was created to make network devices and network protocols interoperable.
It allows components, such as hard drives and video cards, to function in a computer operating theater network independent of the manufacturers. In networking, the OSI model defines how media, protocols, and standards work together.
The OSI mock up breaks the mesh march into sevener administrable layers. It is used American Samoa a universal method for communicating meshing concepts and interpretation network functionality.
Each OSI stratum performs a distinct unmoving of functions. Following the OSI model when artful, construction, upgrading, and troubleshooting will ensure greater compatibility and interoperability 'tween network technologies and vendors.
The OSI model besides makes possible an organized organized come nea to network troubleshooting.
Benefits of the OSI Model
Benefits of the OSI worthy let in:
- Divides the aspects of meshing operations into fewer complex components.
- Standardizes interfaces, enabling engineers to specialize design and development efforts to specific functions.
- Facilitates modular engineering and prevents changes in one area from touching others.
- Ensures interoperability and allows network designers to choose the right networking devices.
- Accelerates evolution and helps with examination and troubleshooting the network.
The first bullet refers to the fact that the OSI model divides networking concepts into sevener hierarchical categories, the OSI layers. Figure 1 illustrates the cardinal layers of the OSI model, which we research next.
Envision 1: Seven Layers of the OSI Model
Seven Layers of the OSI Model
The vii layers of the OSI model begin with bed 1 at the keister. To each one layer only communicates with its neighbor layers. All traffic essential enter and die off through layer 1.
It is important to learn the seven layers in order. Use the mnemonic twist, "Please Arrange Not Throw Sausage Pizza Away" to help remember the septet layers of the OSI model.
The video, TCP/IP and the OSI Mold Explained! (36:34), explains how the OSI Model maps to the TCP/IP protocol, review the purpose of each layer and discusses how the varied network devices are mapped to the TCP/IP protocol.
Physical Bed – Layer 1
OSI layer 1 is the physical layer, illustrated in Figure 2. Two important words to associate with the physical layer are bits and media.
The physical bed is responsible for converting bits from a computer, represented by zeros and ones, into a signalize that can be sent over the network. Signals are propagated over some media: twisted-pair cable, fiber optic cable, coaxial cable, or air.
The somatogenetic layer provides the electrical, mechanical, proceeding, and working means for implementing physical media for the purposes of propagating data via signaling.
Common layer 1 devices include repeaters and hubs. These are considered "dumb" devices because they do not make any decisions about what they are receiving or sending.
Cable installers principally work at the physical layer. A titanic percentage of network problems occur at this layer and should glucinium the opening when troubleshooting the web.
Figure 2: Layer 1 of the OSI Example
Information Tie Layer – Level 2
OSI layer 2 is the information link layer, depicted in Figure 3. The data link layer is responsible for supporting all network protocols that need to diffuse over the physical media.
Layer 2 is also responsible for the speed of transmission system, flow control, and error correction. The link layer uses the physical topology to identify the devices and the media comprising the network. The information connect level is serviced by the physical bed.
The primary layer 2 networking devices are bridges and switches; these devices have some "intelligence service" in this they make decisions about forwarding protocol data units (PDUs).
Bridges are bequest devices, substance that they are rarely used in modern networks. Switches have replaced bridges because switches are faster, have more ports, and support more technologies.
The information associate layer can equal divided into two sublayers:
- Logic link control (LLC) – responsible for underframe synchronization, flow control, and error checking along with identifying protocols like Ethernet Oregon 802.3.
- Media admittance control (MAC) – the interface between the LLC and the physical level, responsible for delimiting bed 2 PDUs, Beaver State frames.
Addressing frames is an life-and-death characteristic of a Layer 2 protocol. The treat associated with a frame is called the physical address.
Ethernet is one type of level 2 communications protocol. Ethernet defines a 48-bit physical address, called a MAC address, to identify a network interface on a computer or network device.
Mackintosh addresses are hex addresses represented in various formats, depending on the operating system of the host device.
The first 24 bits of a Mackintosh address identifies the cause and posture number of the network user interface, and the shoemaker's last 24 bits unambiguously identify the meshing port on the Internet.
Figure 3: Layer 2 of the OSI Model
Network Layer – Layer 3
OSI stratum 3 is the network layer. This is where most of the action takes place in the daylight-to-twenty-four hour period work of networking professionals. The Net exists largely because of the Net Protocol (Information processing), a bed 3 protocol.
Historically, many layer 3 protocols were used for web implementations; but over time IP became the exclusive network layer protocol, so we often make the immediate association of IP with layer 3.
There are two fundamental implementations of IP: IP version 4 and IP variant 6, with IPv6 easy but surely replacing IPv4. The terminus packet, or datagram, is often secondhand when referring to network layer PDUs, like Information processing packets.
The network layer is responsible for conclusion-to-conclusion route determination. Bed 3 mesh design ensures that all IP cover is unique. IPv4 addresses and IPv6 addresses are two examples of mesh addresses or logical addresses.
A network has both a physical and a logical topology; the logical topology is associated with the network layer, and layer 3 addressing provides the hierarchical labeling scheme for the logical network topology.
A subnet is a network that combines with other networks to mannikin a larger net.
The networking device most often related with layer 3 is a router. Routers interconnect to make the skeleton in the cupboard of the Internet. Routers define the networks that comprise the Cyberspace. Routers forward IP packets through the Internet.
Figure 4: Layer 3 of the OSI Model
Ravish Layer – Layer 4
OSI layer 4 is the transport layer, depicted in Figure 5. The transport layer is responsible segmenting application data, regulating the flux of information, and enhance the tone of service (QoS) minimally provided by the network level.
While the electronic network layer is dedicated to moving information between remote networks, the transport layer instantiates and maintains the communicating session specific to an application or service on the two hosts at each goal of the session.
The term segment is often wont to describe transport layer PDUs; for instance, TCP segments and UDP segments are encapsulated by IP packets.
Historically, an array of stratum 4 protocols was used in various types of networks. But the sort of time resulted in the almost linguistic universal adoption of deuce primary transport layer protocols:
- Transport control protocol (Transmission control protocol) – connection-minded protocol with intrinsical reliability mechanisms that guarantee delivery of information between source and destination in virtual circuits, based on prescriptive operations: sliding windows and sequencing and mention of information segments.
- Exploiter datagram protocol (UDP) – a connectionless protocol that sends data without guaranteeing delivery operating theatre acknowledging its receipt. UDP is put-upon with voice and television traffic, and other types of traffic where information technology is not as important to verify the arriver and order of information comprising a communicating session. UDP is often the transport layer protocol of alternative when speed is more important than reliableness.
Layer 4 devices include firewalls. Firewalls non single make decisions about routing packets, but firewalls determine whether information satisfies the policies required to enter a network. The policy requirements are defined by both layer 3 and bed 4 parameters.
Figure 5: Layer 4 of the OSI Model
Session Bed – Layer 5
OSI layer 5 is the session stratum, represented in Figure 6. The session layer is responsible establishing, maintaining, and terminating sessions between deuce computers. This includes opening, stopping, and rhenium-synchronizing ii computers as they communicate, a work called session control .
A keyword to think of for layer 5 is communication. The school term's characteristic of level 5 are analogous to TCP virtual circuits, but involve more body overhead in order to allow greater functionality.
The data link up layer services the network layer. The network layer services the shipping layer. The transport level services the session level. The sitting layer services the presentation layer, which we explore next.
Visualise 6: Layer 5 of the OSI Exemplar
Presentation Bed – Level 6
OSI layer 6 is the introduction layer, depicted in Figure 7. The presentation layer facilitates communication between applications on distinct computer systems in so much a way that the mechanics of the facilitation are transparent to the applications. Layer 6 is responsible for three main functions:
- encryption/decipherment
- compression/decompression
- the phrase structure which defines the communication, such as JPEG for graphics, TXT for text files, MP3 for audio files; wholly devices communicating must be capable to speak the duplicate language to interact.
The terms sentence structure and format are most often associated with the presentation layer. The presentation layer services the application stratum.
Figure 7: Layer 6 of the OSI Good example
Application Layer – Layer 7
OSI layer 7 is the application level, depicted in Calculate 8. The application layer is the layer nearest to the user and provides services to applications put-upon past the endpoint devices. It does not provide services to any other OSI layer.
The World Wide Web (WWW) is a system realized at the application layer of the OSI sit.
The application layer is nigh a great deal related to with services and applications such as Telnet, SSH, FTP, HTTP, HTTPS, and email (SMTP, POP, IMAP).
Word processing software and spreadsheet software are often bundled in an billet software suite, and called office applications; modern-day office applications integrate with the application layer to facilitate sharing of bureau documents over the Internet A a means of real-time collaborationism for project teams.
Figure 8: Layer 7 of the OSI Model
Encapsulation
Encapsulation is the process of placing one PDU inside another PDU for network delivery. See Figure 9.
As information moves down the OSI layers, PDUs are recursively encapsulated in PDUs associated with the single layers. At each phase of encapsulation, headers and footers are prepended and appended to the respective PDU to create a modern PDU.
The process commode be described in Little Phoeb steps, using the PDU terminology we have got adopted:
- Data – Data consists of strings of alphanumerics used away a automatic data processing system diligence.
- Segments – The data is packaged into segments for lengthways transport. By using segments, the transport layer ensures that the message hosts at both ends of, articulate, an electronic mail system can reliably communicate.
- Packets – The segments are encapsulated inside packets, or datagrams, that include network headers with source and terminus logical addresses (usually IPv4 or IPv6).
- Frames – The frames traverse a one-hop singular route directly connecting one network device to some other network gimmick; the hop is one link of a chain of golf links comprising an terminate-to-end network communicating instance. The frame header includes the source and destination natural science addresses mandatory for data link level communication.
- Bits – The binary (electrical or visual) information sent over a medium as signals.
Figure 9: Encapsulation
Summary
In this lesson, the 7-stratum OSI model was introduced. The benefits of exploitation the OSI mock up were explained. Each layer was delineate in some detail.
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Source: https://electricalacademia.com/computer/osi-model-layers-functions/
