ATLAS 550 User Resource Module. Performs BONDing Mode 1 compliant inverse multiplexing in increments of 56/64 Kbps. Module provides 2.048 Mbps of BONDing capacity that can be utilized for one IMUX session at 2.048 Mbps, four IMUX sessions at 512K, or multiple IMUX sessions of varying bandwidth. Does not present any physical interfaces and is a plug-on board for all user interface modules and the resource host module.