This July 2021 issue contains one technical paper, two educational contributions, as well as four editorial notes.

The technical paper, NemFi: Record-and-replay to emulate WiFi, by Abhishek kumar Mishra and colleagues, proposes a trace-driven WiFi emulator called NemFi, that allows modeling of transmission opportunities of uplink and downlink directions, packet loss, frame aggregation, and media access control behavior. The latter two concepts are unique for WiFi when compared with other similar tools that have been built for cellular networks.

The first educational contribution, The Graph Neural Networking Challenge: A Worldwide Competition for Education in AI/ML for Networks, by Jose Suarez-Varela and colleagues, proposes a ”challenge” to teach students about applications of AI/MLin computer networks. The authors describe a process to select a dataset, and a competition-based approach where participants must design a neural-network-based approach to infer properties of the dataset with as much accuracy as possible.

The second educational contribution, P4Pi: P4 on Raspberry Pi for Networking Education, by Sandor Laki and colleagues, presents a novel platform for networking education based on a Raspberry Pi, allowing students to program P4.

Then, we have four editorial notes. The first one, Limited Domains Considered Useful, by Brian Carpenter and his colleagues, argues not only that limited domains have been with us from the very beginning of the Internet but also that they have been shaping innovation of Internet technologies ever since, and will continue to do so.

The second editorial note, Collaboration in the IETF: An Initial Analysis of Two Decades in Email Discussions, by Michael Welzl and his colleagues, discusses the following question: when big players follow such a “shoot first, discuss later” approach, is IETF collaboration still “real”, or is the IETF now being (mis-)used to approve protocols for standardization when they are already practically established, without really actively involving anyone but the main proponents?

The third editorial note, Workshop on Overcoming Measurement Barriers to Internet Research (WOMBIR 2021) Final Report, by kc claffy and her colleagues, reports on the Workshop on Overcoming Measurement Barriers to Internet Research (WOMBIR), held earlier in 2021.

The fourth and last editorial note, A Square Law Revisited, by Brian Carpenter, revisits the approximate apparent growth of the globally addressable Internet in proportion to the square root of the host count.

I hope that you will enjoy reading this new issue and welcome comments and suggestions on CCR Online (https://ccronline.sigcomm.org) or by email at ccr-editor at sigcomm.org.