Layer 6 - Presentation layer

The Network Redirector directs CPU operating system native code to the network operating system. The coding and format of the data may not recognizable by the network operating system. The Presentation layer deals with translation of file formats, encryption of data and compression of data. The data consists of file transfers and network calls by network aware programs.

Figure 1

As an example: when a dumb terminal is used as a workstation in a mainframe or minicomputer network, the network data is translated into and from the format that the terminal can use. The Presentation layer presents data to and from the terminal using special control characters to control the screen display (LF-linefeed, CR-carriage return, cursor movement, etc..). The presentation of data on the screen would depend on the type of terminal VT100, VT52, VT420, etc.

Similarly, the Presentation layer strips the pertinent file from the workstation operating system's file envelope. The control characters, screen formatting and workstation operating system envelope are stripped or added to the file, depending on if the workstation is receiving or transmitting data to the network. This could also include translating ASCII files characters from a PC world to EBCDIC in an IBM Mainframe world. At this point, the data is contiguous and complete at this point (one large data file).

Just a note, Layer 6 is not well defined in actual protocols. Remember the OSI model is just a reference model to aid in understanding interconnecting network with different protocols. For example, layer 6 is incorporated in the Application layer of the TCP/IP protocol.

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Copyright July 2013 Eugene Blanchard