This value reports the memory-usage threshold, in bytes, beyond which the node's storage management considers its resources critically constrained, a more severe level than the warning threshold. Administrators treat used memory exceeding this value as an urgent signal that the APPN node's networking function may soon fail to allocate memory for new sessions or operations. For example, if the memory-used value surpasses this critical threshold, the admin should expect potential session establishment failures until memory pressure is relieved.