PBX-U503 is a new generation of large capacity unified communication. Based on powerful hardware platform, It supports 800 Users and 100 concurrent calls which is integrated voice, video, paging, fax, conference, recording and other useful functions. It also provides four slots to install FXO, FXS, Hybrid FXU and E1/T1 boards by hot-plug mode, so that it can be flexibly configured and combined according to the actual use scenarios.