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OSI protocols are a family of standards for information exchange. These were developed and designed by the International Organization of Standardization (ISO). In 1977 the ISO model was introduced, which consisted of seven different layers. This model has been criticized because of its technicality and limited features.
Each layer of the ISO model has its own protocols and functions. The OSI protocol stack was later adapted into the TCP/IP stack. In some networks, protocols are still popular using only the data link and network layers of the OSI model.
The OSI protocol stack works on a hierarchical form, from the hardware physical layer to the software application layer. There are a total of seven layers. Data and information are received by each layer from an upper layer. After the required processing, this layer then passes the information on to the next lower layer. A header is added to the forwarded message for the convenience of the next layer. Each header consists of information such as source and destination addresses, protocol used, sequence number and other flow-control related data.
The following are the OSI protocols used in the seven layers of the OSI Model: