Draft Document for Review December 5, 2019 4:33 pm 8456ch_DS_HMC_Plan.fm Chapter 8. IBM DS8900F Management Console planning and setup  209 In racked configurations such as model 996 and 994, the rack power control is done through  the Ethernet managed intelligent power distribution units (iPDUs). For rackless configurations  such as model 993, the iPDUs are optional. Intelligent Power Distribution Units Figure 8-5 ME external connections An HMC communicates to these iPDUs via ethernet network and manages and monitors  system power state, iPDU configuration, System AC power on/off, iPDU firmware update,  iPDU health check/error and power usage reporting. The iPDUs network interfaces are also connected to the external ports of the ME to reach the  black and gray network switches. They are distributed over the black and gray network. That  means iPDUs that belong to one power domain (usually left side at the rear of the rack)  connect to gray network switch and the iPDUs which belong to other power domain (usually  right side at the rear of the rack) For Agility class racked models 996, there is the possibility to add an expansion rack model  E96. Two cascaded switches are added to the base frame to connect the additional iPDUs of  the expansion rack to the ME switches.  One 1U 24-port ethernet switch is added for the black network and one 24-port is added for  the gray network. Each of them has an uplink to the related ME switch port of their designated  black or gray network. The 2U space required is already reserved at the bottom of the base  rack. Figure 8-6 and Table 8-1 show how each port is used on the pair of DS8900F ME Ethernet  switches. 