RECN-DD: A Memory-Efficient Congestion Management Technique for Advanced Switching

As VLSI technology advances, the interconnection network represents a larger percentage of the total system cost and power consumption. In fact, a current trend in network design is to reduce the number of components. However, this leads to systems working closer to saturation point, and therefore an efficient congestion management technique is required. In that sense, RECN has been recently proposed for advanced switching (AS). RECN detects the formation of congestion trees and dynamically allocates queues for storing congested packets, thus, eliminating the HOL blocking introduced by congestion trees. These queues are deallocated when congestion vanishes. We have identified two shortcomings that may affect RECN scalability and implementation. Firstly, although RECN allocates queues in an efficient way, resource deallocation is performed in-order, thus losing efficiency and wasting resources. This leads to an excessive requirement of memory at switch ports. Secondly, both allocation and deallocation mechanisms involve the use of specific control packets not supported by the AS standard, thus preventing RECN implementation. In this sense we provide a detailed description of the current RECN deallocation mechanism. In this paper we present an enhanced RECN version (RECN-DD) where these problems have been eliminated. Specifically, we propose a new distributed queue deallocation mechanism that reduces the number of required resources and does not require the use of control packets. Moreover, we propose a new congestion notification mechanism that does not require non-standard AS packets. Instead, flow control packets are used to notify congestion, thus simplifying the implementation of RECN-DD in AS