| Subject | English | German |
| gen. | U interface | Leitungsschnittstelle |
| commun. | U interface | U-Schaltstelle |
| gen. | U interface | Teilnehmerschnittstelle U |
| gen. | U interface | Bezugspunkt U |
| commun. | Uk0 interface | Uk0-Schnittstelle (U interface for ISDN BA copper circuit to local ISDN exchange) |
| commun. | UM interface | UMSchnittstelle (air interface betw. BTS and MS, GSM Series 04) |
| commun. | UP0 interface | Upo-Schnittstelle (U interface for ISDN BA 2-wire circuit, for ping pong transmission to/from local exchange) |
| commun. | U-interface circuit | U-Schnittstelle (network-side interface for 2-wire circuit, ISDN) |