OSI model

Week 5

This week have been given three suggestion for the blog-entry:
1. The OSI Reference model
2. The TCP/IP protocol suite
3. Simple Network Management Protocol
So I considered and decided to describe the OSI model shortly.
First of all I am going to write about the OSI model. OSI is short for Open System Interconnection, an International Organization for Standardization standard for worldwide communications that defines a networking framework for implementing protocols in seven layers that I will define next:
1. Physical layer. The physical layer defines the electrical and physical specifications for devices. In particular, it defines the relationship between a device and a transmission medium, such as a copper or optical cable. This includes the layout of pins, voltage, cable specifications, hubs, repeaters, network adapters, host bus adapters.
2. Data link layer. The data link layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the physical layer.
3. Network layer. This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. In addition internet protocols routing and forwarding are functions of this layer.
4. Transport layer. This layer provides transparent transfer of data between systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer. Typical examples of Layer 4 are the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).
5. Session layer. This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.
6. Presentation layer. This layer provides independence from differences in data representation (e.g.: encryption) by translating from application to network format. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.
7. Application layer. This layer supports application and end-user processes. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level.




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