When installing or upgrading from the DVD iso on a laptop, not connected by
wire, there is no standard option to setup a wireless connection. The automatic
network setup does not result in a network connection, when only WiFi is
available.

There is a workaround to disrupt the installation/upgrading and using Settings
to setup a wireless connection. After that it is not so obvious to return to
the installation/upgrading process.

The advantage of having a network connection is that during
installation/upgrading newer packages get downloaded from the update
repositories. This is even more required when upgrading is used to repair an
almost fully updated system, where newer packages get replaced by the packages
from the iso image, which need to be updated afterwards.

It would be even more easy if the data for the network connection are read from
an already existing system; the system to be upgraded.

I needed this to recover, after updating one system on a multi-boot computer,
which left the other systems not bootable. The recovery was to use the iso to
"upgrade" the non-bootable system.