The prime objective of QoS is to define transmission ordering and scheduling on the RF interface. Fragmentation is an upstream cable modem capability. When enabled for a service flow, fragmentation is initiated by the CMTS when it grants bandwidth to a particular modem. The grant size must be smaller than the corresponding bandwidth request from the modem. Baseline privacy, if enabled, is performed on each fragment, as opposed to the complete original MAC frame.
Similar rules apply to the differential fiber-optical or electrical spacing.
For the downstream frequency plan the cable is assumed to have a passband with a lower edge at 96 MHz and an upper edge that typically is between 300 and 864 MHz. Within that passband, analog TV signals in 8 MHz channels are assumed to be present, as well as other narrowband and wideband digital signals. For upstream, the cable system is assumed to have a passband of 5-65 MHz. Analog signals in 8 MHz channels may be present, as well as other signals. Clearly, ANSI adoption of these standards will go far toward making true interoperability and retail modem sales a reality.