If you can easily understand how the network is working you will have more time to think how to make improvements on that system, and not spend all the energy on learning and getting to figure out the things that are already done. On the other side, this layered model will guarantee you that your new technology incorporated into some new protocol, or version of protocol, will be able to function and cooperate with all other protocols in the same or other layers. This is why we need The OSI network reference model.The Open Systems Interconnection model is a networking reference model. OSI model was made by the International Organization for Standardization to provide a framework on which to build a suite of open systems protocols. The goal was that this set of protocols would be used to develop an international network that would not be dependent on proprietary systems. OSI specifications are in use today, the seven-layer OSI model has made major contributions to the development of protocols and products for all types of new networks.
In the simple words, OSI model helps to easily learn, explain and use knowledge about networking protocols and they technology. It does that by simplifying the understanding of protocol cooperation. The OSI model provides an extensive list of functions and services that can occur at each layer. It also describes the interaction of each layer with the layers directly above and below it. Although the content of this course will be structured around the OSI Model the focus of discussion will be the protocols identified in the TCP/IP protocol stack.
The technical expression “protocol” can come in front of your eyes whenever you will try to have understanding about the network communication. Actually, it is similar to a language that is communal by scores of people. A protocol may turn into a standard if the concerned players in a game will agree-on to do so. And finally, on the protocol’s approval, it can be announced as an official standard. The same case is with the OSI 7 Layers model which is an agreed-upon “language” with reference to their syntaxes, and definitions. Its usage means that two or more than two parties are agreed on to exchange data or information with its help.
The ISO is a simple model; used for the purpose of networking. That is followed a defining layers approach. It is a seven levels model for the computer’s networking. Moreover, each layer is leaned on in a stack pattern; one layer is resting-on the other layer. But the job of every one layer is particular in nature. Each is assigned with a specific charge. Anyway, you can understand this model after having the know how of each layer, named as: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer. Below is the detail of each layer:
The uppermost layer is application layer that is positioned at the 7th level of ISO model. This protocol’s functionality is involved “file transferring”, and “display formatting” etc. In other words, 7th layer is application-specific and it will provide a particular data format according to your program needs. Http, DNS, SMTP and FTP are the layer7 protocols. But sometimes, Application Layer is suggested as the part of the session layer or presentation layer especially when the synchronization in a file transfers process takes place or when sessions are created etc.
|6. Presentation layer protocols:|
Presentation layer as layer 6 of ISO model is almost held in reserve for clear-cut data manipulation tasks. Moreover, reliable data is to be encapsulated for transmission with its help. At this layer, messages exchange can be made and transformation from ASCII could possibly be made. Some other functions like security with encryption form, compression and requests for creation and termination of sessions is performed at this point.
|5. Session layer protocols:|
Session layer’s job is included: to be involved with the session establishment as dealings with half duplex session cases. Besides this, checksums process is performed as data synchronization part at this layer. Session layer is also dealt with the session transmission and provides a guaranteed communications within a session and this task is done by permitting only one user at a time.
|4. Transport layer protocols:|
Transport layer executes certain jobs like to avoid a high-speed sender from overflowing data to a slow receiver, to generate a specific connection presently that is needed by the Layer 5 (session layer), and this layer is accountable for keeping on the track multiple connections. Since, more than one connection may take place simultaneously. Therefore, this layer can keep the incoming as well as leaving data packets appropriately addressed so to be passed on to their intended locations. Furthermore, use of special checksums methods for the connection reliability is performed at this layer. But keep this in your mind that both reliable also unreliable connections are proficient to use the checksum technique because transport layer can make available a sufficient amount of information within the packets which are error free along with identified routing order.
|3. Network layer protocols:|
Networking Layer is complex by nature. And these complications can come in front of you when you will talk about its utilities. For example, layer 3 is in-charge, first and foremost with the data routing function such as data transfer from the transport layer (layer 4) to a distant location. And there can be a possibility that subjected remote location isn’t sharing the same physical layer (1st layer) direct-link. There can also be a chance that the data-link layer protocol may become smaller as a result of the IP fragmentation of the TCP/IP protocols suite. Anyway, networking layer can provide statistical data for the purposes of formulating charges, headed for parties and the functions like optimizing links, arguing in support of bigger pricier pipes; smaller cheaper pipes, bigger slower pipes; smaller faster pipe etc.
Data Link Layer
Data Link is the ISO model’s 2nd layer. Its main function is to provide a reliable data transfer from corner to corner via data links, being used. This layer received the raw data from 1st layer (physical layer) in order to make the physical link as a reliable connection. Data Link Layer endows with the techniques to make the link active as well as to uphold it. Most of all, all higher layers can enjoy a guarantee about the error free data reception from this layer. But the data detection and recovery is made soon this layer received data from first physical layer.
Data Link Layer is using the HDLC (high Level Data link Control) and LLC (Logical Link Control) protocols for the services providing purposes. For point to point and multi point data links, HDLC protocol is being used. You can use it in a number of different ways because it is a general purpose data link control protocol. But a reliable data transfer is performed by LLC within two connecting communication bodies. Well! This layer is always ready to handle the problems in the case of frames or cells duplication. Resolving damaged packets problems; performing checksum method for finding out bad frames or cells and to address fast transmitter problems, all these issues is handle by data link layer. Some examples of its protocols that function mostly are Ethernet, TokenRing, and PPP.
|1. Physical layer protocols:|
At the physical level, following jobs are performed:
- Guarding of the shared media’s moving bits
- Details are provided regarding how to use the channel and the possible channels can be full duplex, half duplex, or else simplex.
- Conductor mapping is done at this level in the case of wired media. But if media involved is wireless then frequency, amplitude or cycle-offsets are suitable for mapping the receiving etc.
Certain key terms are very important with respect to the OSI layers. These are such as: “ARP” (Address Resolution Protocol) that is used by a network layer protocol to transform IP (internet protocol) addresses into physical addresses.
But “Broadcast” word is referred to the procedure of sending messages to each link on a specific network. The term “MAC” (Media Access Control) works at the MAC layer for right to use control purpose.