Technical data

3.2.1.2 Logical Data Exchange
FDL services are available for issuing jobs. Jobs are transferred via the
specified communication relations (logical channels as connection) to the
communication partner in PDUs.
To the user, it appears as if the application processes exchange data
directly. In fact, the data are passed down from layer 2 on one side,
transmitted on the physical medium and passed up again to layer 2 through
the communications layers.
3.2.2 Communication Relations
From the point of view of the user, communication with the application
processes of the communication partner takes place on logical channels.
These logical channels to the communication partners are defined in the
configuration phase.
For each communication relationship the following information is stored:
➣
address of the remote station
➣
local and remote service access point
Application
process
Application
process
1
2
1
2
DEVICE X
DEVICE Y
transparent
Data exchange
Layer 2
physical data
transmission
Fig. 3.5 Logical Data Exchange
B8976060/02 Fundamentals of the Model
3 - 7 Volume 1