From my point of view, there are the following options to enable landline telephony in a multi-storey single-family house:
Option 1 -- Move TAE connection to the ground/first floor
Usually, the access point for the Internet connection (whether by DSL, cable, or fiber optic) is located in the basement of the house. In the case of an DSL connection, this would be the TAE socket, to which the router (more precisely the DSL modem) must be connected. Technically, this TAE socket can of course also be moved to another floor.
If the router (as with a Fritzbox) is also supposed to act as a DECT base station, the Fritzbox can also be easily placed outside the basement, where the DECT range is more favorable. However, the disadvantage of this variant is that you are tied to the location of the TAE socket in a living area, and other network components (patch panel, switch, NAS, etc.) may again have to be located elsewhere (e.g., in the basement), and thus not in the same place as the router.
Option 2 -- DECT repeater
A fairly simple solution if the DECT base station is in the basement is a DECT repeater. AVM offers a suitable DECT repeater for about 70 euros, which only needs to be placed at a suitable location in a power socket. Suitable means: ideally between the base station (Fritzbox) and the point that should still receive the DECT signal at the greatest distance.
The disadvantage of this solution is that such a DECT repeater causes additional costs in acquisition and operation, requires a suitable power outlet in a favorable location, and then blocks it there. Furthermore, it must be known that the AVM DECT repeater only supports built-in encryption of DECT telephony between AVM devices (Fritzbox and Fritzfon), but not with third-party manufacturers (e.g., Gigaset).
Option 3 -- Second Fritzbox
Using a second Fritzbox that also supports DECT telephony is quite popular with some households. For example, one Fritzbox could be set up as an Internet access point in the basement, while another functions as a WLAN and DECT access point on the upper floor. AVM's FritzOS now offers very comfortable mesh features, which makes configuration easy and significantly less prone to errors.
The disadvantage of using a second Fritzbox is that it also ideally needs to be supplied with a LAN connection and a power connection and thus takes up space in the room. Also, a phone can only ever be connected via DECT to one of the two Fritzboxes at a time. Roaming between the radio cells, as is common with WLAN today (e.g., walking from the attic to the basement), is therefore not possible. Speed dials are also limited to one Fritzbox.
Option 4 -- Separate DECT station
It is not necessarily required to use the Fritzbox’s built-in DECT station. There are also separate DECT base stations, such as the Gigaset Pro N670 IP DECT for about 100 euros. This is very well developed and specifically designed for its purpose. It also allows power supply via Power-over-Ethernet (PoE) and is therefore not dependent on a separate power outlet.
The disadvantage of this variant is that you are then moving into a different ecosystem. This means that you cannot access the convenient services of the Fritzbox such as the integrated address book or answering machine (including notification by mail). Likewise, the quite charming features of a Fritzfon are no longer usable, and the DECT connection between a Fritzfon and such a DECT base station would take place unencrypted.
For the address book, however, the Gigaset solution at least offers access to an external address book via LDAP, which could, for example, be stored on a local NAS. For the answering machine, some internet providers such as 1&1 also offer central solutions. So it is a matter of weighing the pros and cons.
Option 5 -- Extend DSL signal via LAN cable
The last option listed here requires a double socket to which the Fritzbox can be connected. It is called a double socket because the DSL signal is first extended to the first connection, where the Fritzbox expects the DSL signal, and then the second connection enables the network to access the Internet.
Specifically, it looks like this: if the TAE socket is in the basement, you can lead the (RJ45) end of the DSL cable from there to the connection on the patch panel that leads to the Fritzbox. At the other end, a regular patch cable then leads the signal from the connection socket to the DSL input of the Fritzbox. This way, the DSL signal is simply extended via the installation cable.
Now a second patch cable must run from the Fritzbox to the second connection socket so that the router (the Fritzbox) is also made available on the network. Of course, a switch at the patch panel must interconnect the individual network connections.
The disadvantage of this variant is that a place with a double socket and a power outlet must also be “sacrificed” for the Fritzbox. However, the Fritzbox itself offers further network ports that can be used directly at that location.
If there are many double sockets distributed throughout the house, you are more flexible in placing the Fritzbox (and thus also the DECT base station). And if you ever want to use a different solution or no longer need DECT, you can simply remove the Fritzbox again.
CONCLUSION
If you do not have a DSL connection, some options fall away. In our single-family house, we also use a Fritzbox as a DSL modem and for DECT telephony. For WLAN, however, we use three Unifi NanoHD access points. We initially used option 5, which worked well. Since I did not find the setup very tidy, I tried placing the Fritzbox in the server cabinet in the basement. And indeed, this still gets us the DECT signal even in the attic. Furthermore, AVM also offers the FritzFon app -- as a result, the smartphone always rings on an incoming call, which is usually always with you, and we only rarely use the Fritzfon anymore.