This paper reviews the design and implementation of several video telephony systems at Bellcore as a case study in iterative design.In contrast to single user compuer applications, communication systems consists of both the interconnection technology and the people who are interconnected. From a user's point of view, the capabilities provided by the system, the rules for its use, and its reaction to their actions depend jointly on what its developers implemented and how other users behave. This fact has wide-ranging implications for system design, use, and evaluation.In reviewing our design experience, we identify four dilemmas for iterative design that flow from the inherently social nature of communication systems. We conclude with methodological and theoretical suggestions to supplement conventional iterative design principles as applied to communications systems.

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The purpose of this pre-registered study was to investigate how different ideological groups justified and mobilised collective action online. We collected 6878 posts from the social media accounts of pro-Black Lives Matter (n = 13) and anti-Black Lives Matter (n = 9) groups who promoted collective action in the month after George Floyd's murder and the Black Lives Matter (BLM) protests and counter-protests. We used content analysis and natural language processing (NLP) to analyse the content and psychological function of the posts. We found that both groups perceived their action as 'system-challenging' , with pro-BLM accounts focused more on outgroup actions to mobilise collective action, and anti-BLM accounts focused more on ingroup identity. The reverse pattern occurred when the accounts were attempting to justify action. The implications are that groups' ideology and socio-structural position should be accounted for when understanding differences in how and why groups mobilise through online interactions.