The Crosspoint-Queued Switches with Virtual Crosspoint Queueing

Scalable high speed routers and switches implemented with distributed units introduced a large RTT latency between the line cards and switch fabric, making the crosspoint buffer requirement impractical to provide 100% throughput for unbalanced traffic on combined input and crosspoint queued (CICQ) switches. Crosspoint Queued (CQ)-only switches remove this RTT latency by completely eliminating the need of flow control between the line cards and switch fabrics. This study shows that the CQ-only switches are prone to frequent packet loss in unbalanced traffic common to realistic Internet traffic. CQ switches with virtual crosspoint queues (VCQs) is proposed and investigated to minimize this problem. Each of VCQs unit associated with a set of CPs with the same upstream link functions as a dynamically sharable buffer that can maximize the use of its limited memory space inside the switch fabric. Furthermore, the all memory units in the proposed switch operate at the line rate, making the implementation practical. Unlike the CICQ switch, the CQ switches with VCQs do not require flow control between the line card and switch fabric. Simulation results show that the CQ switch with VCQs can achieve high throughput for unbalanced traffic and significantly reduce packet loss pertinent to the CQ-only switch.