Multi-tiered shaping allowing both shaped and unshaped virtual circuits to be provisioned in a single virtual path

摘要

The invention utilizes two-stage shaping and two-priority queuing thereby allowing both shaped and unshaped virtual circuits to be provisioned in a single virtual path. For each VP, a separate dynamic buffer is set up for each shaped VC and unshaped VC within the VP. The shaped cells stored in dynamic buffers are dequeued via VC scheduling (first stage shaper) to a high priority queue according to the shaped VC contracts, and the unshaped cells stored in dynamic buffers are dequeued in a round robin manner to a low priority queue. The outputs of both the high priority queue and the low priority queue are passed to a second stage shaper where cells from the high priority queue are scheduled according to the VP contract, and cells from the low priority queue are also scheduled according to the VP contract, but only when VP bandwidth is not being used by the high priority cells. In order to avoid overrunning the high priority queue in the second stage, the iPSR (Peak Shaping Rate increment) of the CBR VCs in the VP is chosen to be the iSSR (Sustained Shaping Rate increment) of the VP. The iPSR of the CBR VCs in the VP can be chosen to be higher than the iSSR of the VP as long as cell loss is not experienced at the second stage caused by overrunning the high priority queue. In addition, the calculated bucket for CBR service in the first stage is made a function of the Peak Cell Rate (PCR) of the VP.