I don't use it as I have a fixed IP.. and so can access from anywhere I like directly to the TC.. but did you use the basic apple instructions.
Did you fulfill all the requirements? The Mac's at each end must be Lion.. and the TC must be 7.6.1 firmware.
Is the TC the main router? If not have you opened the required ports listed in the apple article. Once you do that it should connect. Perhaps try computer to computer first.. then see if you can reach the TC.
If the TC is not the main router.. then the ports must be opened on the router you do have.. we have no idea what that is.. you will need to read the manual.. but that will be the issue.. !!
You will need to check with a forum for the router how to open ports if you don't know.
I also suggest if you have no idea.. employ a tech for an hour.. why people think they should be able to solve every computer network issue I do not know.. it is a washing machine.. when it breaks do you fix it or call the tech.. why not treat computer and networks the same??
By turing on Back to My Mac in System Preferences > iCloud, the right ports should open.
I think there is an issue right now.
However, you can read this article http://support.apple.com/kb/HT4907 to see if it helps.
You can access the TC without icloud.. you simply forward port 548 TCP to the TC which is in bridge. No setting on the TC but you should have a decent disk password or something as the security for this is very low.
I would be very surprised if the modem does not have upnp. Almost every modem and router produced in the last few years will have it. I don't read German so you will need to see if you can understand it.
Just google for that model and you will find the pdf manual.
A lot of the German ISP use static IP.. if they do, and you have static public ip, this is a trivial setup. But call a tech.. they could manage it with their eyes shut.
Sorry I cannot understand German..
If the modem cannot see the TC.. which is working and plugged in by ethernet..
Is the TC bridged? It has to be to do this.
Is the TC using DHCP? It should be otherwise the routing table in the speedport may have issues.. What IP is the TC getting from the speedport?? Check if there is arp table info in the speedport that it has the TC correctly listed. Although it is perhaps not hugely significant.. have you setup the TC with SMB compliant names.. remember the rest of the world is SMB.. and a network name has to be short, no spaces, absolutely no apostrophe.. use pure alphanumeric characters.
Once you get the TC recognised by the speedport you should then be able to port forward to it.
You might need to lock the IP by dhcp fixed host.. or locked IP .. there are several names. but where a dynamic address is locked to the MAC address of the client.
A computer tech I still think could do this in an hour or less. How many hours have you spent so far??
I'll share my view, considering that MobileMe has ceased to exist and now Back to My Mac is iCloud based. I'm able to access my TC's drive remotely on my MB with the following setup:
- ISP's modem in bridge mode (if you can't access the modem's configuration, contact your ISP for assistance).
- TC configured to "Create a Wireless Network" (in AirPort Utility, you can enable this in the 'Wireless' tab).
- In the 'Base Station' tab, go to the lower part 'Back to My Mac' and add your iCloud ID.
- Update your TC.
- On your Mac, go to System Preferences > iCloud and enable Back to My Mac.
This should do it. I don't know if this works when your modem manages the internet connection and the TC is in bridge mode. If I can get around to test that alternative, I'll let you know.
Also, I have to be clear that this doesn't work for making Time Machine backups remotely to your TC (I'm still trying to find out how to do that), it only allows you to access your TC's drive remotely (i.e. the 'Data' drive).
Hope this helps.