IPNext 190 System Installation GuideAddPac Technology Proprietary & Documentation 132 - 33Connecting Digital E1 Interface (optional)E1 port connects the external PSTN with RJ-45 standard cable.E1 port is the interface, which provides RJ-45 connector to connect PSTN and the standard Public Automatic BranchExchange (PABX).RJ45 to PBXCablePBXFigure 2-4 Connecting Digital E1