Previous example of not so secret, LEAKED/BLOWN joint BND-NSA (Wiesbaden) Fiber-Backbone operation graphics --
https://4.bp.blogspot.com/-TTUqTA4ymXA/VWy8RxKJSfI/AAAAAAAACeI/ACRKxD5ALdQ/s1600/eikonal-authorities.jpg
Disclosures from Austria On May 15, 2015, Peter Pilz, member of the Austrian parliament for the Green party, disclosed an e-mail from an employee of the Deutsche Telekom unit for lawful intercept assistance (Regionalstelle für staatliche SonderAuflagen, ReSa), who notified someone from BND that apparently a particular fiber-optic cable had been connected to the interception equipment. The e-mail describes this cable as follows:
Transit STM1 (FFM 21 - Luxembourg 757/1), containing 4 links of 2 Mbit/s:
Channel 2: Luxembourg/VG - Wien/000 750/3
Channel 6: Luxembourg/CLUX - Moscow/CROS 750/1
Channel 14: Ankara/CTÜR - Luxembourg/CLUX 750/1
Channel 50: Luxembourg/VG - Prague/000 750/1
STM1 stands for Synchronous Transport Module level-1, which designates a transmission bit rate of 155,52 Mbit/second. A similar multiplexing method is Wavelength-Division Multiplexing (WDM) commonly used in submarine fiber-optic cables. The latter having a much larger capacity, generally STM-64 or 9,5 Gbit/second.
The number 757 is a so-called Leitungsschlüsselzahl (LSZ), which denotes a certain type of cable. In this case it stands for a channelized STM-1 base link (2 Mbit in 155 Mbit), which seem to be used for internal connections.
According to the meanwhile updated LSZ List, the number 750 stands for a "DSV2 Digitalsignal-Verbindung 2 Mbit/s", which is a digital signal path.
The cable mentioned in the e-mail therefore only has a small capacity, which seems to indicate that NSA and/or BND selected it carefully.
FFM 21 stands for "Frankfurt am Main 21", which according to Deutsche Telekom's network map is the name of the Point-of-Presence (PoP) located at its facility in the Frankfurt suburb Nied - the location where that Eikonal tapping took place.
This means we have a physical cable running between Luxembourg and the Deutsche Telekom PoP in Frankfurt, but containing channels to cities which are much further, so they have to connect to channels within other physical cables that run from Frankfurt to Moscow, Prague, Vienna and Ankara, respectively:
Notice -- Channel 6: Luxembourg/CLUX - Moscow/CROS 750/1
According to Pilz, the full list contains 256 cable links. 94 of them connect EU member states, 40 run between EU members and other European countries like Switzerland, Russia, Serbia, Bosnia-Herzegovina, Ukraine, Belarus and Turkey. 122 links connect European countries with nations all over the world, with Saudi Arabia, Japan, Dubai and China being mentioned most.
The country which most links (71) run to or from is the Netherlands. The list for that country was disclosed by Peter Pilz during a press conference in Brussels on May 28, 2015. The US, the UK and Canada are not on the list, although there were apparently 156 links from/to Britain too.
Updates: On June 25, 2015, the Dutch telecommunications provider KPN announced the results of its inquiry into the alleged tapping of its cables. It was very difficult to identify the channels in the list because meanwhile KPN's whole network had been restructured. Eventually it became clear the connections (being channels within cables and KPN only being responsible for the first half until Frankfurt) had been rented out under telephony wholesale contracts, so it was impossible to trace individual customers or users.
Leaked documents were not attributed to Snowden,
https://www.electrospaces.net/2015/05/new-details-about-joint-nsa-bnd.html
At the time, a number of CONUS and OCONUS analysts believed high level NSA poc's, acting under orders from within the Obama administration (Hillary Clinton), in or around 2009-2010, transferred this information (in much greater detail), as well as other ongoing operation's, and much more to Moscow.