Explain the function of each layer of the OSI model
The OSI reference model is built, bottom to top, in the following order: physical, knowledge link, network, transport, session, presentation, and application. The physical layer is classified as Layer one, and the top layer of the model, the application layer, is Layer 7.
Physical Layer (Layer 1)
The physical layer of the OSI model identifies the network’s physical characteristics,including the following specifications:
Hardware: The type of media used on the network, such as type of cable, type of connector, and pin out format for cables.
Topology: The physical layer identifies the topology to be used in the network. Common topologies include ring, mesh, star, and bus.
In addition to these characteristics, the physical layer defines the voltage used on a given medium & the frequency at which the signals that over the knowledge operate. These characteristics dictate the speed & bandwidth of a given medium, as well as the maximum distance over which a definite media type can be used.
Data Link Layer (Layer 2)
The knowledge link layer is responsible for getting knowledge to the physical layer so that it can be transmitted over the network. The knowledge link layer is also responsible for error detection, error correction, and hardware addressing. The term frame is used to report the logical grouping of knowledge at the knowledge link layer.
The data link layer has two distinct sub-layers:
Media Access Control (MAC) layer:- The MAC address is defined at this layer. The MAC address is the physical or hardware address burned in to each network interface card (NIC). The MAC sublayer also controls access to network media. The MAC layer specification is included in the IEEE 802.1 standard.
Logical Link Control (LLC) layer:- The LLC layer is responsible for the error & flow-control mechanisms of the information link layer. The LLC layer is specified in the IEEE 802.2 standard.
Network Layer (Layer 3)
The primary responsibility of the network layer is routing providing mechanisms by which information can be passed from network process to another. The network layer does not specify how the information is passed, but provides the mechanisms to do so. Functionality at the network layer is provided through routing protocols, which are application parts. Protocols at the network layer are also responsible for route choice, which refers to determining the best path for the information to take throughout the network. In contrast to the information link layer, which makes use of MAC addresses to communicate on the LAN, network layer protocols use application configured addresses and special routing protocols to communicate on the network. The term packet is used to report the logical grouping of information at the network layer.
Transport Layer (Layer 4)
The basic function of the transport layer is to provide mechanisms to move knowledge between network devices. Primarily it does this in ways:
Error checking: Protocols at the transport layer ensure that data is sent or received correctly.
Service addressing: Protocols such as TCP/IP support many network services. The transport layer makes sure that data is passed to the right service at the upper layers of the OSI model.
Segmentation: To traverse the network, blocks of knowledge need to be broken in to packets that are of a manageable size for the lower layers to handle. This technique, called segmentation, is the responsibility of the transport layer.
Protocols at the Transport Layer
Protocols that operate at the transport layer can either be connectionless, such as User Datagram Protocol (UDP) , or connection-oriented, such as Transmission Control Protocol (TCP). For an additional discussion of these protocols, and of the difference between connection-oriented and connection less protocols, refer to the later section "Connection less and Connection-Oriented Protocols."
Flow Control
The transport layer is also responsible for knowledge flow control, which refers to how the receiving tool can accept knowledge transmissions. common methods of flow control are used:
Error checking: Protocols at the transport layer ensure that data is sent or received correctly.
Service addressing: Protocols such as TCP/IP support many network services. The transport layer makes sure that data is passed to the right service at the upper layers of the OSI model.
Segmentation: To traverse the network, blocks of knowledge need to be broken in to packets that are of a manageable size for the lower layers to handle. This technique, called segmentation, is the responsibility of the transport layer.
Protocols at the Transport Layer
Protocols that operate at the transport layer can either be connectionless, such as User Datagram Protocol (UDP) , or connection-oriented, such as Transmission Control Protocol (TCP). For an additional discussion of these protocols, and of the difference between connection-oriented and connection less protocols, refer to the later section "Connection less and Connection-Oriented Protocols."
Flow Control
The transport layer is also responsible for knowledge flow control, which refers to how the receiving tool can accept knowledge transmissions. common methods of flow control are used:
Buffering:
When buffering flow control is used, knowledge is temporarily stored and waits for the location tool to become available. Buffering may cause a controversy if the sending tool transmits knowledge much faster than the receiving tool can manage it.
Windowing:
In a windowing environment, data is sent in groups of segments that require only one acknowledgment. The size of the window (that is, how many segments fit into one acknowledgment) is defined when the session between the two devices is established. As you can imagine, the need to have only one acknowledgment for every, say, five segments can greatly reduce overhead.
Session Layer (Layer 5)
The session layer is responsible for managing and controlling the synchronization of information between applications on devices. It does this by establishing, maintaining, and breaking sessions. Whereas the transport layer is responsible for setting up and maintaining the connection between the nodes, the session
layer performs the same function on behalf of the application.
Presentation Layer (Layer 6)
The presentation layer's basic function is to convert the information intended for or received from the application layer in to another format. Such conversion is necessary because of how information is formatted so that it can be transported across the network. Applications cannot necessarily read this conversion. Some common information formats handled by the presentation layer include the following:
Graphics files: JPEG, TIFF, GIF, and so on are graphics file formats that need the information to be formatted in a sure way.
Text and information: The presentation layer can translate information in to different formats, such as American Standard Code for Information Interchange (ASCII) and Extended Binary Coded Decimal Interchange Code (EBCDIC).
Sound/video: MPEG, MP3, and MIDI files all have their own information formats to and from which information must be converted.
Another important function of the presentation layer is encryption, which is the scrambling of information so that it can't be read by someone other than the intended recipient. Given the basic role of the presentation layer that of data-format translator it is the obvious place for encryption and decryption to happen.
Graphics files: JPEG, TIFF, GIF, and so on are graphics file formats that need the information to be formatted in a sure way.
Text and information: The presentation layer can translate information in to different formats, such as American Standard Code for Information Interchange (ASCII) and Extended Binary Coded Decimal Interchange Code (EBCDIC).
Sound/video: MPEG, MP3, and MIDI files all have their own information formats to and from which information must be converted.
Another important function of the presentation layer is encryption, which is the scrambling of information so that it can't be read by someone other than the intended recipient. Given the basic role of the presentation layer that of data-format translator it is the obvious place for encryption and decryption to happen.
Application Layer (Layer 7)
In simple terms, the function of the application layer is to take requests & knowledge from the users & pass them to the lower layers of the OSI model. Incoming knowledge is passed to the application layer, which then displays the knowledge to the users. A number of the most basic application-layer services include file
& print capabilities.
The most common misconception about the application layer is that it represents applications that are used on a method such as a web browser, word processor, or spreadsheet. In lieu, the application layer defines the processes that.enable applications to use network services. For example, if an application needs to open a file from a network drive, the functionality is provided by components that reside at the application layer.
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