In order to avoid multiple cabling systems in the building for

• ISDN telephones,
• Analogous telephones and
• PC network connections,

I equipped the appropriate rooms with universal cables according to Category-5. The diagram to the right shows how to connect RJ45 outlets with 4 pairs of wires = 8 wires. For this purpose, only LAN outlets can be used, although ISDN outlets (IAE) look alike, they are equipped with 4 usable contacts only.

For ISDN the pairs 1 and 3 are used, for analogous telephones the pair 2 (and sometime 4) are used. This setup enables to run ISDN and analogous telephones in parallel using a single Cat-5 cable. The PC LAN wiring (Ethernet Local Area Network) uses the pairs 2 and 3, which means, it cannot get combined with another service.

---

The cellar serves as wiring hub; from there 2 Category-5 cables lead to each outlet according to the following diagram:

At the ISDN private branch exchange, where you also find outlets for analogous telephones, so-called "Y cables" are used, which connect both the ISDN and the analogous outlet to one RJ45 connection. Because of this, at the other end of the cable you can connect both, an ISDN PC adapter as well as an analogous telephone concurrently.
In parallel to this, all PCs are networked by connecting the appropriate Ethernet adapter with the central Ethernet hub.
Of course, all connections can get re-patched in the cellar when necessary.