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.