  In current Data Center Networks (DCNs), Equal- Cost MultiPath (ECMP) is used
as the de-facto routing protocol. However, ECMP does not differentiate between
short and long flows, the two main categories of flows depending on their
duration (lifetime). This issue causes hot-spots in the network, affecting
negatively the Flow Completion Time (FCT) and the throughput, the two key
performance metrics in data center networks. Previous work on load balancing
proposed solutions such as splitting long flows into short flows, using
per-packet forwarding approaches, and isolating the paths of short and long
flows. We propose DiffFlow, a new load balancing solution which detects long
flows and forwards packets using Random Packet Spraying (RPS) with help of SDN,
whereas the flows with small duration are forwarded with ECMP by default. The
use of ECMP for short flows is reasonable, as it does not create the
out-of-order problem; at the same time, RPS for long flows can efficiently help
to load balancing the entire network, given that long flows represent most of
the traffic in DCNs. The results show that our DiffFlow solution outperforms
both the individual usage of either RPS or ECMP, while the overall throughput
achieved is maintained at the level comparable to RPS.
