Manual VIPA CPU 21x Chapter 4 Deployment of the CPU 21x-2BT10 with TCP/IP
HB103E - Rev. 05/45 4-5
Layer 5 Session layer
The session layer is also called the communication control layer. It relieves
the communication between service deliverer and the requestor by
establishing and holding the connection if the transport system has a short
time fail out.
At this layer, logical users may communicate via several connections at the
same time. If the transport system fails, a new connection is established if
needed.
Additionally this layer provides methods for control and synchronization
tasks.
Layer 6 Presentation layer
This layer manages the presentation of the messages, when different
network systems are using different representations of data.
Layer 6 converts the data into a format that is acceptable for both
communication partners.
Here compression/decompression and encrypting/decrypting tasks are
processed.
This layer is also called interpreter. A typical use of this layer is the terminal
emulation.
Layer 7 Application layer
The application layer is the link between the user application and the
network. The tasks of the application layer include the network services like
file, print, message, data base and application services as well as the
according rules.
This layer is composed from a series of protocols that are permanently
expanded following the increasing needs of the user.
Layers
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