Cabling: Add fiber interconnect information

docs/case2.0/cabling.md

@@ -11,6 +11,8 @@ Considerations regarding network connection can be found in the [Network Setup](
 
 This cabling diagram contains all connections between modules and devices (but not the inner workings of the modules): ![](img/voc-case2_0-cabling.png)
 
+Note: This cabling diagram doesn't show the option to connect lectern and FOH modules via fiber yet.
+
 ## Network Setup
 
 A VOC lecture hall setup needs some internal VOC network (commonly named VOC-VLAN, even though it may not always be a VLAN technically) and a way to have internet access.
@@ -42,6 +44,18 @@ When the server case is used, the router VM will provide uplink to the whole VOC
 If not, deploy one WRT router in a lecture hall or the VOC office providing a connection between public and VOC network.
 (Remember to enable all hall networks which are reachable via this router so that the remote access VPN works. TODO: Where is this documented?)
 
+## Fiber between FOH and Lectern
+
+We prepared the option to use a fiber run between lectern and FOH module in 2026-11 (but the fiber is not available yet).
+Both sides use E2000/ LSH connectors, but you can also unplug the patch cables from the switch and SDI fiber converters and plug in a twin fiber with LC connectors instead.
+
+Both sides use fiber core A for SDI and fiber core B for the network trunk.
+Both links use bi-directional optics for the links, so that we only need a twin fiber for both connections.
+
+- The SDI link uses a 1270/1330 nm (lavender) SFP module for on the lectern side and TODO (blue) on the FOH side
+- The network link uses a 1330/1270 nm (blue) SFP module for on the lectern side and TODO (lavender) on the FOH side
+
+
 ## FOH Module
 
 ![](img/voc-case2_0-foh-back.jpeg)