It is possible to install Debian over network with a little help of another person in remote location. I performed it only once and it was some time ago, but the whole procedure is quite easy and straightforward.

Boot installation media

Boot installation media. You can safely use netinst minimal image.

Start expert installation

Open Advanced options menu.

Execute Expert install menu entry.

Choose language

Execute Choose language option.

Select language.

Define country.

Define default locales.

Define additional locales.

Define keyboard settings

Choose Configure the keyboard.

Select keymap.

Mount installation media

Choose Detect and mount CD-ROM.

Select additional modules to load.

Load network-console installer component

Choose Load installer component from CD.

Select network-console installer component to load.

Detect network hardware

Choose Detect network hardware.

Configure network

Choose Configure the network.

Use DHCP or provide network settings by hand.

Define hostname and domain name.

Configure remote access

Choose Continue installation remotely using SSH.

Set password for installer user and verify it.

Notice the fingerprint of SSH server's host key.

Access remote machine

Use SSH to access remote server.

Continue installation process remotely.