Scalably Testing Congestion Control Algorithms of Real-World TCP Implementations

New TCP congestion control algorithms are being developed and deployed in the Internet. However, it is challenging to test their correctness mainly due to the scalability problem caused by the extremely large number of test inputs. In this paper, we propose a scalable testing method, called SCCT, which tackles the scalability problem using two techniques. 1) SCCT tests only the congestion control algorithms of TCP at the interface level instead of the whole TCP at the packet level. 2) SCCT exercises an equivalence class of test inputs simultaneously using symbolic execution, instead of a single test input at a time. Both techniques can improve the scalability by many orders of magnitude. Our Linux TCP experiments on seven congestion control algorithms show that SCCT is scalable and quickly detects multiple Linux bugs that have not been reported before.