What is osi model in networking pdf

In a network, the MAC layer controls how devices gain access to media and are allowed to transmit data. In the Open Systems Interconnection OSI model, seven layers are used to communicate over a network by computer systems.

In the early s, all major computer and telecommunications companies adopted it as the first standard for network communications. OSI is a reference model for technology vendors and developers so they can create digital communications products and software programs that can interoperate and promote a clear framework for describing the functions of networking and telecommunications systems.

Relationships can be understood as models based on conceptual frameworks. Data is sent and received over a network using the OSI reference model. Layers are broken down into seven segments in this model. Data is sent and received by each layer of the network. Messages must be sent through all of the layers in order to reach their destinations. Standardization is an international organization that is ISO. An entire communication system is comprised of seven layers or levels.

Layers represent the physical medium that carries traffic between two nodes. You might use an Ethernet cable or Serial cable as an example. Username or Email Address. Remember Me. Blog Post. Elaine , 2 months ago 0 5 min read Table of contents 1. What Is Osi Model Ppt? What Is Osi Model Explain? A physical connection e. A data link e. The network e.

The session e. The following are examples of presentation e. Why Is Osi Model Used? How Does Osi Model Work? The second layer is a data link that connects to the third layer. The third layer is called Layer 3, which is not. Touch is the fourth layer of transport. The seventh layer is an application of alligator.

For example, a layer that provides error-free communications across a network provides the path needed by applications above it, while it calls the next lower. OSI had two major components: an abstract model of networking, called the Basic Reference Model or seven-layer model, and a set of specific protocols. The concept of a seven-layer model was provided by the work of Charles Bachman, Honeywell Information Services.

The new design was documented in ISO and its various addenda. In this model, a networking system was divided into layers. Within each layer, one or more entities implement its functionality. Each entity interacted directly only with the layer immediately beneath it, and provided facilities for use by the layer above it. Protocols enabled an entity in one host to interact with a corresponding entity at the same layer in another host. Service definitions abstractly described the functionality provided to an N -layer by an N-1 layer, where N was one of the seven layers of protocols operating in the local host.

Introduction The Open System Interconnection OSI reference model is a framework for defining the conventions and tasks required for network systems to communicate with one another. In the work of the two organizations was combined, and a single document describing the reference model for Open Systems Interconnection was produced.

The purpose of the OSI model was to assist vendors and communications software developers to produce interoperable network systems. Although the OSI model was designed to replace all previous computer communications standards, it is no longer viewed as such a replacement. Rather, the OSI model has succeeded as a tool for describing and defining how heterogeneous network systems communicate. The OSI model is based on a widely accepted structuring technique called layering.

According to this approach, the communications functions are partitioned into a vertical set of layers. Each layer performs a related set of functions, utilizing and enriching the services provided by the immediately lower layer. An important task in the development of the OSI model was to group similar functions into layers, while keeping each layer small enough to be manageable, and at the same time, keeping the number of layers small, since a large number of layers would increase the processing overhead.

The principles used in defining the OSI layers are summarized in following list Stallings, : 1. The number of layers should not be so many as to make the task of describing and integrating the layers more difficult than necessary.

Layer boundaries should be created at points where the description of services is small and the number of interactions between boundaries is minimized. Separate layers should be created in cases where manifestly different functions are performed or different technologies are involved. Similar functions should be collected into the same layer. A layer should be created where functions are easily localized.

This enables the redesign of the layer to take advantage of new technologies. A layer should be created where there is a need for a different level of abstraction in the handling of data.

Changes of functions or protocols of a layer should be made without affecting other layers. For each layer, boundaries with its upper and lower layers only are created. The application of the above principles resulted in the seven-layer OSI reference model, which we describe next. Layer 1 is the lower layer in this model. The added framings make it possible to get the data from a source to a destination. Some orthogonal aspects, such as management and security, involve every layer.

Security services are not related to a specific layer: they can be related by several layers, as defined by ITU-T X. These services are aimed to improve the CIA triad confidentiality, integrity, and availability of transmitted data. In practice, the availability of communication service is determined by the interaction between network design and management protocols.

Appropriate choices for both of these are needed to protect against denial of service. It defines the relationship between a device and a physical transmission medium e.

This includes the layout of pins, voltages, line impedance, cable specifications, signal timing, hubs, repeaters, network adapters, host bus adapters HBA used in storage and more.

This channel can involve physical cabling such as copper and optical fiber or a wireless radio link. Layer 2: Data Link Layer The data link layer provides reliable transmission of data frames between adjacent nodes, built on top of a raw and unreliable bit transmission service provided by the physical layer. To achieve this, the data link layer performs error detection and control, usually implemented with a Cyclic Redundancy Check CRC.

Note that the data link layer provides reliable transmission service over a single link connecting two systems. If the two end systems that communicate are not directly connected, then their communication will go through multiple data links, each operating independently. In this case, it is the responsibility of higher layers to provide reliable end-to-end transmission. Bridges, which connect two similar or dissimilar local area network segments, operate at this layer. Layer 3: Network Layer While the data link layer deals with the method in which the physical layer is used to transfer data, the network layer deals with organizing that data for transfer and reassembly.

In short, the main function of this layer is Path determination and logical Addressing. This layer provides logical addresses to the packets received which in turn helps them to find their path. In addition to message routing, the network may or may not implement message delivery by splitting the message into several fragments, delivering each fragment by a separate route and reassembling the fragments, report delivery errors, etc.

Although the services provided by a transport protocol are similar to those provided by a data link layer protocol, there are several important differences between the transport and lower layers: 1. Thus, the transport layer should be oriented more towards user services than simply reflect what the underlying layers happen to provide. Similar to the beautification principle in operating systems. Negotiation of Quality and Type of Services: The user and transport protocol may need to negotiate as to the quality or type of service to be provided.

A user may want to negotiate such options as: throughput, delay, protection, priority, reliability, etc. Guarantee Service: The transport layer may have to overcome service deficiencies of the lower layers e. Addressing becomes a significant issue: That is, now the user must deal with it; before it was buried in lower levels. For what types of service does this work? While this works for services that are well established e.

Use a name server. Servers register services with the name server, which clients contact to find the transport address of a given service. In both cases, we need a mechanism for mapping high-level service names into low-level encoding that can be used within packet headers of the network protocols.

In its general Form, the problem is quite complex. One simplification is to break the problem into two parts: have transport addresses be a combination of machine address and local process on that machine.