This read-write integer from 0 to 100 caps the maximum percentage of downstream bandwidth that can be allocated to constant-bit-rate traffic; the description clarifies this is a ceiling that denies service to acquiring ComPorts if it would be exceeded, not a guarantee that percentage will actually be used, and the default of 100 means no real control. It protects downstream capacity from being entirely consumed by CBR services like voice, reserving headroom for best-effort data even as CBR demand grows. For example, an operator worried about telephony growth crowding out data subscribers might set hcxMaxDnstrmCBRAlloc to 50 so CBR traffic can never claim more than half the downstream, even though it might normally use far less.