Technical data

3.2.1 Communications Model
This section is intended to introduce you to the communications world and
to provide explanations of the model and terminology to establish the
relationship between theory and practice.
In terms of communication, an application process includes all the
programs, resources and tasks not assigned to a communication layer.
These include, for example, operating systems, real application processes,
application programs and communication drivers.
3.2.1.1 Relationship between Application Processes
There are logical relationships between application processes which are
used to exchange information. These communication relations must all be
established before data exchange begins. An application process can
participate in communication via communication end points. One or more
communication end points are assigned on a fixed basis and uniquely to an
application process. These are addressed by the application process using
local communication references (address of the communication end point).
The communication references are specific to a device. Between two
application processes, there are one or more communication relationships
which are uniquely assigned to communication end points (see Fig. 3.4).
Application
process
A
Communication
relation
Application
process
B
Application
process
C
1
20
7
22
9
OO
O
O
Communication
end point no. 20
O
12
O
Fig. 3.4 Relationship Between Application Processes
Fundamentals of the Model B8976060/02
Volume 1 3 - 6