Polycom Part # 2215-23367-001. This module adds ISDN PRI capability to your Polycom HDX videoconferencing system. A PRI Line has 23 channels and thus it is especially popular if you want to handle multi-point calls over ISDN as it allows for multi-site calls at 384kbps over ISDN without the need for an external bridge (assumes that the HDX unit is also multi-point enabled). It also allows for very high call rates up to 1472kbps over ISDN in point-to-point calls making Full HD over ISDN a reality.