NOX: Towards an Operating System for Networks. Natasha Gude et al. ACM SIGCOMM CCR, 38(3):105–110, Jul. 2008.
Both papers are in the area of Networks but they differ greatly in that the first paper designs a protocol whereas the second paper proposes a system architecture. In addition, the network protocol introduced in paper  is designed for a particular environment, in contrast to the operating system in paper  that uses more general approach. For another comparison, paper  is much more detailed than paper  providing more specific and larger amount of clues.
The authors of paper  makes an important observation that existing TCP protocol does efficiently handle network flows of the data center network, which requires: low latency for short flows (foreground traffic), and high utilization for long flows (background traffic). Naive processing of the flows reduces the overall performance since flows of high bandwidth dominate buffers at the switches thereby make the system drop flows of low latency. Based on the observation, they propose a variant of TCP protocol, Data Center TCP (DCTCP). Their design is simple: using a flag in the Explicit Congestion Notification (ECN) feature- that is already included in TCP protocol – determine the threshold K, and keep buffer occupancies low using K. Through various evaluations, they prove that this strategy gives the same or improved throughput than TCP maintaining the buffer size to be %90 less. Reducing packet dropping ratio DCTCP allows the applications to handle background traffic faster without affecting foreground traffic.
Paper  claims that it is currently difficult to manage a network through low-level configuration of individual components, thereby suggests a centralized operating system NOX that provides a programming interface to observe and control a network. According to its architecture, NOX keeps a single network view in a database and a separate server that controls all the switches. Programmers can think of the network as network in a single machine while writing programs in a high-level language; Python. By showing simple example applications, the authors illustrate NOX’s programming model. For a particular application, called Ethane, implementation without NOX takes about ten times more lines than one with NOX.