This read-create Integer32 defines the new physical-layer bandwidth, presumably in bits per second, for the downstream (network-to-customer) direction of the CP-IWF. It lets an admin provision or adjust the downstream capacity independently of the upstream setting, since the two directions can differ. An asymmetric service plan might set this to a higher value than cpIwfUpstreamPhysicalBandwidth to give the customer more downstream than upstream capacity.