文档介绍：How OSI Works
by Jeff Tyson
Virtually works in use today are based in some fashion on the Open Systems
Interconnection (OSI) standard. OSI was developed in 1984 by the anization
for Standardization (ISO), a global federation of national anizations representing
approximately 130 countries.
The core of this standard is the OSI Reference Model, a set of seven layers that define the
different stages that data must go through to travel from one device to another over work. In
this article, you'll find out all about the OSI standard.
The Layers
Think of the seven layers as the assembly line in puter. At each layer, certain things
happen to the data that prepare it for the next layer. The seven layers, which separate into two
sets, are:
• Application Set
Layer 7: Application - This is the layer that actually interacts with the operating
system or application whenever the user chooses to transfer files, read messages
or perform work-related activities.
Layer 6: Presentation - Layer 6 takes the data provided by the Application layer
and converts it into a standard format that the other layers can understand.
Layer 5: Session - Layer 5 establishes, maintains and munication with
the receiving device.
• Transport Set
Layer 4: Transport - This layer maintains flow control of data and provides for
error checking and recovery of