Microsoft KB Archive/103886
Article ID: 103886
Article Last Modified on 7/30/2001
This article was previously published under Q103886
STANDARD DATA FLOW ARCHITECTURE
The OSI model presents a standard data flow architecture, with protocols specified so that layer N at the destination station receives exactly the same object that was sent by layer N at the source station.
- The sending process passes data to the application layer which attaches an application header (AH).
- The presentation layer may transform the data in various ways, and possibly add a header to the front, before giving the result to the session layer. The presentation layer aware of which portion of the data given to it by the application layer is AH, if any, and which portion is actual user data. Nor does it need to know.
- This process is repeated until the frame reaches the data link layer, where, in addition to a header, a trailer (DT) is added to aid in frame synchronization. The frame is then passed down to the physical layer, where it is actually transmitted to the receiving station.
- On the receiving station, the various headers (and DT) are stripped off one by one as the message is passed up the layers until it finally reaches the receiving process.
Remember that although the actual data transmission is vertical, each layer is programmed as though it were really horizontal. When the sending transport layer, for example, gets a message from the session layer, it attaches a transport header and sends it to the receiving transport layer. From its point of view, the fact that it must first hand the message to the network layer on its own machine is technically unimportant.