July 2, 2020

As the number, variety, and sophistication of Internet applications keeps growing and the number of client requests per time unit keeps increasing, datacenters are adopting hyperscale computing solutions to scale with the demand, and provide appropriate support for interactive services. As system size increases, the cost of the interconnection network grows faster than system size, thus becoming increasingly important to carefully design it to prevent overprovisioning. However, by doing so, the network operation point moves closer to saturation, and sudden traffic bursts may lead to congestion. This situation is aggravated by the recent introduction of flow control in datacenter networks to cope with RDMA requirements. The result is a massive performance degradation whenever some network region becomes congested. Moreover, performance degradation may remain for long even after the traffic bursts that congested the network have already been transmitted. This performance degradation is not compatible with trustworthiness. In this keynote, I will show why congestion appears in an interconnection network, how it propagates, and why performance may degrade so dramatically. Different kinds of congestion will be identified. Also, a global solution to address the congestion problem will be proposed. It consists of several complementary mechanisms that cooperate to address all kinds of congestion and operate at different time scales. Some of these mechanisms have been recently incorporated into commercial products and are being standardized. Keywords: Interconnection network, congestion management, datacenters