Troubleshooting large computer systems is often highly collaborative. Because these systems consist of complex infrastructures with many interdependent components, expertise is spread across people and organizations. Those who administer such systems are faced with cognitive and social challenges, including the establishment of common ground and coordination of attention, as they troubleshoot in collaboration with peers, technical support, and software application developers. We take a

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... ed cognition approach to interpreting a specific instance of problem-solving in administering a web-based system, examining the movement of representational state across media in a single system administrator's environment. We also apply the idea of language use as joint activity to understand how discourse attributes affect what is accomplished collaboratively. Our analysis focuses on information flow among participants and other sources, and how these affect what information is attended to, transmitted, and used. Colle. The core issue turned out to be a misunderstanding of the meaning of internal-port, as specified when creating the new player instance. The internal-port is used for communication from maestro to player-that is, the port on which player "listens" for data from maestro. Admin had originally believed that internal-port was used from communication in the opposite direction: from player to maestro. Because Admin had asked the network team to configure the firewall to allow communication in the wrong direction, the problem was an inconsistancy between the firewall rules and the player's port specification. The solution was either to change the firewall rules, or to change the player's ports. Admin eventually chose the latter solution (specifying the player's internal-port as 7236 rather than 7137), as shown in Fig. 4 .