There is a scarcity of scientific literature about the characteristics of the control work and its demands in the critical domain of telecommunication. The motivation of the paper is to shed light on the context and content of the human operators' work in maintaining the dependability of telecommunication networks. A case study was accomplished in a large telecommunication company. The research focused on clarifying the impact of human operators on the dependability of telecommunication network. Interviews confirmed earlier assumption among members of the communication network operations (CNO) community that the human operator has an important impact on the network dependability. Specific sources of errors in daily work were identified and strategies of avoiding erroneous action were described. By utilising core-task analysis and modelling approach, we defined generic control demands of the CNO work domain, and operators' ways of coping with these demands. Regarding human dependability of communication network operations, a combination of resilient and proactive ways of acting is needed. Due to daily changes in the network and the continuous increase of its complexity, specifically change management on both organisational and work practice levels was required. The study is restricted to one Finnish telecommunication company, which limits possible empirical generalisation of the findings.