OSI Layers

The Open System Interconnect (OSI) Reference Model.

The table below displays the layers defined within the Open System Interconnect (OSI) Reference Model. The OSI Reference Model or OSI layers consists of 7 layers (with each layer apart from the lowest layer, consisting of software), each performing a higher level of functionality than the previous one, and stacked on top of each other – hence the OSI Reference Model sometimes being referred to as a protocol stack.

7  Application Layer
6  Presentation Layer
5  Session Layer
4  Transport Layer
3  Network Layer
2  Data Link Layer
1  Physical Layer


  • TCP/IP Network AdministrationCraig Hunt – O’Reilly & Associates, Inc – ISBN: 0-937175-82-X
  • Getting Connected: the Internet at 56K and UpKevin Dowd – O’Reilly & Associates, Inc- ISBN: 1-56592-203-4
  • Practical UNIX and Internet SecuritySimson Garfinkel & Gene Spafford – O’Reilly & Associates, Inc – ISBN: 1-56592-148-8