What Is a Business Reference Model?

The reference model in network term refers to the OSI reference model, a set of universally applicable specifications developed by ISO (International Organization for Standardization), so that computer platforms around the world can conduct open communication.

The reference model in network term refers to the OSI reference model, a set of universally applicable specifications developed by ISO (International Organization for Standardization), so that computer platforms around the world can conduct open communication.

ISO has created a communication model that helps to develop and understand computers, the Open System Interconnection OSI reference model. The OSI reference model divides the network structure into seven layers:

Reference model communication between two systems

The function of each layer of the OSI reference model can be tracked from the demonstration process of mail lookup in the service. Once you log on to the network and open your mail program, you can choose to accept mail. At this point, the application layer will recognize your choice and propose a request packet to get data from the remote node, and the application layer passes the request to the presentation layer. The presentation layer first determines whether and how to format or encrypt data requests from the application layer. After that, it will add the required transformations and code for formatting and pass the request to the session layer.

The session layer receives the formatted request and assigns it a data tag. This tag is a dedicated control frame that indicates to the rest of the network that you have permission to transmit data. The session layer passes data to the transport layer. At the transport layer, your data and the control information accumulated so far will be divided into manageable data blocks in preparation for packing into frames at the data link layer. If the data is too large to fit in a frame, the transport layer divides it into smaller blocks and arranges a sequence identifier for each data block. After that, the layer passes data to the network layer one by one.

The network layer adds address information to the data from the transport layer so that the next layer can know the source and destination addresses of the data. Thereafter, the network layer passes the data block with the address information to the data link layer. At the data link layer, data blocks are packed into a single frame. As you know, frames are a structured format for sending small pieces of data. Because each frame has an internal error checking function, using frames will reduce the probability of data loss and errors in the network. The error checking algorithm used in a frame is called FCS (Frame Check Sequence), and it is inserted by the data link layer to the end of the frame.

Reference model inter-layer addressing

Data link layer addresses are fixed serial numbers associated with network hardware and are usually determined before leaving the factory. These addresses are called MAC addresses after passing through the MAC (Media Access Control) sublayer located in the data link layer. It is appended to the destination physical address of the data frame. The address of the network layer residing in the network layer of the OSI reference model can gradually reduce the address range because of the subset of data contained therein, so a hierarchical addressing scheme is adopted, and the address can be specified by the operating system software. ^[4]