Het OSI-model

Wat is het OSI-model The seven-layer model (OSI) and the TCP / IP reference model have much in common. Both describe a set of general guidelines and implementations of specific network protocols to enable computers over the network to communicate with each other. The OSI model which stands for Model for Open Systems Interconnection, consists of 7 Act. The DoD model or TCP / IP model consists of 4 Act, the layers perform the same functions as the seven layers of the OSI model. A reminder to remember the OSI: ALL PEOPLE SEEM TO NEED DATA PROCESSING Why the OSI model

When at the end of the nineteen 70 and the beginning of the nineteen 80 the use of networks was still in its infancy, the development was very chaotic. Companies recognized the benefits of using networks set up networks, but they discovered quite quickly that the expansion of these networks was problematic. That's because different networks were built to different standards. Some companies themselves have developed a standard for network communication that later proved often difficult to reconcile with the standards of other networks. hence the need for a common standard was born. In 1984 bracht the International Orginasation for Standardization (ISO) the OSI model as a charter for the development of network equipment and software. The OSI model is currently the most widely used model for data on a network.

Layers of the OSI Model

1 physical layer: The physical layer describes the mechanism and electrical characteristics of the network. cable types, plugs, the tension on the cables, the manner in which cables are to be braided are part of the physical layer. Flow control passes a cable with electrical signals. Voltage Series correspond to zeros and ones of the binary system. (Low voltage = 0, high voltage = 1). On the physical layer, data is consider in bits, either binary.

2 Data link layer: The data link layer provides the functionality needed to reliably transfer data between network devices on a network. The data link layer uses MAC or hardware’ addresses to send data to the right place. On a network each device has its own unique MAC address embedded in the device (in the case of a PC is the MAC address embedded in the network). The best-known technique that works at the data link layer is Ethernet. Ethernet is a technology that uses MAC addresses to transfer data in a network. Switches and network devices are in low 2 work of the OSI model. The data on low 2 is divided 'frames'. Frames are data units which are provided with a header in which the MAC addresses are recorded from the sender and the receiver.

3 network layer: The network layer provides the functionality that is needed in order to transmit data between the networks,. The network layer is responsible for routing, ‘flow control’ and error handling. Routers operate at low 3 of the OSI model. The most important protocol of the network layer is the Internet Protocol (IP). Routers use IP addresses to control the traffic between different networks. Among other computers, routers and printers have an IP network alongside a MAC also an IP address. The data on low 3 is divide into packets. Packets are data units which include the IP address of the sender and (final) receiver are included.

4 transport layer: The transport layer provides data transfer between two end-users with the help of error control, re-transmission and "flow control’ (timing). The transport layer ensures that higher layers (software from the application layer, for example) do not take into account the accuracy and timing of the data transmission. The most important protocol at the transport layer is the Transfer Control Protocol. TCP provides a connection between two stations on a network and correct data transmission between the stations. The data units on low 4 called segments. In a segment include the port number via which is communicated from the sender and the receiver recorded.

5 session layer: where low 1 to 4 mainly engage in the packaging (and unpacking) of data and addressing is the session layer, the first layer which is directly engaged with the software that makes use of the network. The session is low, maintains and disconnects sessions between two programs.

6 presentation layer: The presentation layer acts as a translation layer which speak one language between two programs. A network can accommodate all types of operating systems, such as Windows, Linux on Apple. These operating systems may use a different representation of the data. The presentation layer on the sending computer translates data from the application layer (7) the common language before it flows into lower layers and is sent. The presentation layer on the receiving computer translates data from the session layer (5) to the language layer by the program on the application (7) is understood. In addition to translating the presentation layer provides compression and encryption of data. The presentation layer is not always used, because translate, encryption or compression may not always be necessary.

7 application layer: The application layer is the layer that is used by network programs. These can be browsers, FTP clients, or e-mail programs. Such programs make use of protocols that run on the application layer such as HTTP (used by the web browser), SMTP (used e-mail programs) FTP (used by FTP clients).