E1 to 4x 10Base-T Interface or called Protocol Converter is a high performance, remote, self-learning Ethernet Bridge. Its compact size and low cost make it ideal for cost-sensitive bridging applications or as a LAN extender over bit stream type infrastructures. Its E1 data interface also provides an economical digital access solution for E1 and Fractional E1 network Services, which can work at data rates of 64Kbps to 2048Kbps.User data is placed into the E1 frame, using only the required number of timeslots. Timeslot assignment is accomplished according to the Data Port speed and manual setting of DIP switches. The main E1 link may be clocked from the recovered receive clock or from an internal oscillator. For easy to check the fault of network line, the device provides loop selection, both local loop and remote loop.