e for handling exceptions, configuration, management, system updates, and SO on. The RSP handles the classification and analysis results of the FPP's work on the incoming PDUs. This happens over 64 logical input ports. In addition to the PDU, it comes in the form of a transmit com- mand from the FPP that essentially instructs the RSP as to how to handle the specific PDU. The ter proceeds by identifying the necessary processing for each PDU. The PDU is added to a queue and stored into the PDU SDRAM. The transmit command determines the QoS, the CoS, and the required PDU modifications for the RSP. The RSP supports up to 65,535 (64K) programmable queues. Each queue is based on program- mable QoS and CoS criteria for processing and routing. It can schedule independently up to 256 log- ical output channels mapped onto 32 physical output ports. It can also connect to an external overriding scheduler that can monitor and schedule all RSP queues. It interfaces downstream with a potential fabric interface controller over a configurable industry-standard 32-bit POS-PL3 or UTOPIA 3 interface. This output can be configured to be one 32-bit interface, two 16-bit interfaces, or four 8-bit interfaces. The RSP has fully programmable packet-discard policies (including Random Early Detection [RED], Weighted RED [WRED], and Early Packet Discard [EPD] algorithms) and outgoing packet data modification capabilities. It is also equipped with intrinsic support for multicast packets and vir- tual paths and has the native ability to segment (which is handy for interfacing with cell-based fab- rics or ATM/POS-PHYs) and cope with real-time traffic such as variable first-rate-real-time (VBR-rt). The RSP has the following four major areas of functionality: Queuing. Traffic management. Traffic shaping. Packet modification. Figure 7.3 shows the hierarchy of criteria applied for the scheduling the RSP. Up to 16 CoS queues feed a single QoS queue to support PDU-based shaping policies. Each QoS queue is assigned to a sin- gle scheduler that is conf