The paper contributes a TCP-like protocol called DCTCP for use in data centers on commodity switches. By using ECN (Explicit Congestion Notification) from the network, it reduces TCP buffer space occupation by 90%.
Again, a key requirement when designing DCTCP was that it be implementable in existing hardware. It seems this is a common thread and a necessary condition for success.
While the demands of a data center environment can be extreme, some differences from wide area networks ease constraints on the protocol design.
The main idea is rather ordinary: react to congestion in proportion to the extent of the congestion. This idea is also used in delay-based congestion control algorithms.
Windows are reduced by a factor depending on the fraction of packets that are marked as congested.
The clever bit is deriving multi-bit feedback from a sequence of single-bits.