These are the end-points of a few E1's, i.e. 2Mbps lines. In Germany, an ISDN bearer channel has 64 kbps (in both directionss). In America, it has often just 56 kbps. (They reserve some bits for in-band signalling. Europe uses a separate "D" channel with 16kbps for all signalling purposes.)

So, the ISDN Basic Rate Interface (BRI) provides a bandwith of 2B+1D = 144kbps in Germany.

The ISDN Primary Rate Interface (PRI) consists of 30 64kpbs B channels plus a 64kbps channel for signaling. (The 32nd channel evaporates on timing everything.) So a PRI gives you nearly 2Mbps bandwith. If used as a single leased-line, the thing is here also called S2M or E1. This compares a bit to the American T1 line which is just 1.5Mbps.

There's a red light on the second E1. That is because it isn't operative yet -- the customer is just upgrading from a 128kbps line.