The 7705 SAR provides a per-VC queuing architecture on the 16-port T1/E1 ASAP Adapter card, 32-port T1/E1 ASAP Adapter card, and 2-port OC3/STM1 Channelized Adapter card with atm/ima encapsulation. The 7705 SAR provides a per-VC queuing architecture on the 4-port OC3/STM1 Clear Channel Adapter card and 4-port DS3/E3 Adapter card with atm encapsulation. In the egress direction toward the ATM port, the scheduling priority at the ATM layer is as follows.
CBR VCs are always shaped and are scheduled with strict priority over all other service categories.
rt-VBR VCs are always shaped and are scheduled next with strict priority over nrt-VBR and UBR VCs.
nrt-VBR shaped VCs are scheduled next with strict priority over nrt-VBR unshaped VCs and UBR VCs.
nrt-VBR unshaped VCs and UBR VCs are scheduled as a common class. Scheduling among these VCs is done using a Weighted Round Robin (WRR) scheduler, where the weight of each VC is determined by the configured SIR for nrt-VBR and by the MIR for UBR VCs. The scheduling is work-conserving, so each VC has access to excess bandwidth in proportion to its SIR/MIR. Under congestion, the performance of each VC degrades proportionally to the weight of the VC.