The OSI model Essay Example for Free

The OSI model Essay Question: Write a 2-3 page paper describing the OSI model and how it relates to a network. Your response should include answers to the following: †¢ On which layers of the OSI model do WAN protocols operate? †¢ What are some of these protocols? †¢ On which OSI layers do switches and routers operate? †¢ If routers reside at more than one layer, what is the difference between the OSI layers? Introduction: The OSI model was introduced in 1984. Although it was designed to be an abstract model, the OSI model remains a practical framework for todays key network technologies like Ethernet and protocols like IP. The OSI model defines internetworking in terms of a vertical stack of seven layers. The upper layers of the OSI model represent software that implements network services like encryption and connection management. The lower layers of the OSI model implement more primitive, hardware-oriented functions like routing, addressing, and flow control. In the OSI model, data communication starts with the top layer at the sending side, travels down the OSI model stack to the bottom layer, then traverses the network connection to the bottom layer on the receiving side, and up its OSI model stack. How OSI model relates to a network: Information being transferred from a software application in one computer system to a software application in another must pass through the OSI layers. For example, if a software application in System A has information to transmit to a software application in System B, the application program  in System A will pass its information to the application layer (Layer 7) of System A. The application layer then passes the information to the presentation layer (Layer 6), which relays the data to the session layer (Layer 5), and so on down to the physical layer (Layer 1). At the physical layer, the information is placed on the physical network medium and is sent across the medium to System B. The physical layer of System B removes the information from the physical medium, and then its physical layer passes the information up to the data link layer (Layer 2), which passes it to the network layer (Layer 3), and so on, until it reaches the application layer (Layer 7) of System B. Finally, the application layer of System B passes the information to the recipient application program to complete the communication process. Interaction Between OSI Model Layers A given layer in the OSI model generally communicates with three other OSI layers: the layer directly above it, the layer directly below it, and its peer layer in other networked computer systems. The data link layer in System A, for example, communicates with the network layer of System A, the physical layer of System A, and the data link layer in System B. The following figure illustrates this example. Figure : OSI Model Layers Communicate with Other Layers On which layers of the OSI model do WAN protocols operate? A WAN protocols is a data communication protocols which is use in the data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN Protocol in WAN technologies, generally function at the lower three layers of the OSI reference model which layers are as following: †¢ Physical layer †¢ Data link layer, and †¢ Network layer. Following figure illustrates the relationship between the common WAN technologies and the OSI model. Figure : OSI Model Layers and WAN Technology specification What are some of these protocols? some protocols which are also operated in the WAN technology are PPP, X.25 etc. On which OSI layers do switches and routers operate? The Network Layer of the OSI model is responsible for establishing paths for data transfer through the network and router are the devices which are used to establishes the path for data transfer. So, routers operate at the Network Layer. And Data Link Layer of the OSI model is responsible for communications between adjacent network nodes. Hubs and switches operate at the Data Link Layer. If routers reside at more than one layer, what is the difference between the OSI layers? Routers generally do not reside at more than one layer, because the router devices are operated in the network layer and they can apply the data link headers when they switch the packet interface and put the signals at the physical layer wires . In this way the routers do work on three different levels, but each job is separate and distinct per layer.