Hi @all,

first thanks for your answers.

The entry which make it more clean that the modell in my mind is to
easy was the example of Robert. If an application will send data over
TCP/IP stack it must determine which transport kind (TCP/UDP/ICMP)
will be used, it must set the source and destination port and it must
inform the IP layer the source IP and destination IP. With other words
the lower layer must be "configured". On the receiving side it must be
the same. Otherwise the application layer can not figure out if the
data are for this application. I do not know how I came yesterday to
the conclusion that this is done automatically. *lol*

Regards,
Markus