Efficient per-flow queueing in DRAM at OC-192 line rate using out-of-order execution techniques

Modern switches and routers often use dynamic RAM (DRAM) in order to provide large buffer space. For advanced quality of service (QoS), per-flow queueing is desirable. We study the architecture of a queue manager for many thousands of queues at OC-192 (10 Gbps) line rate. It forms the core of the “datapath” chip in an efficient chip partitioning for the line cards of switches and routers that we propose. To effectively deal with bank conflicts in the DRAM buffer, we use pipelining and out-of-order execution techniques, like the ones originating in the supercomputers of the 60s. To avoid off-chip SRAM, we maintain the pointers in the DRAM, using free buffer preallocation and free list bypassing. We have described our architecture using behavioral Verilog (a hardware description language), at the clock-cycle accuracy level, assuming Rambus DRAM. We estimate the complexity of the queue manager at roughly 60 thousand gates, 80 thousand flip-flops, and 4180 Kbits of on-chip SRAM, for 64 K flows