A realtime kernel supports realtime communications between communicants operating on respective network nodes. The realtime kernel handles the complex tasks of connecting to communicants, virtual areas, and other network resources, switching those connections in response to user inputs, and mixing realtime data streams. The realtime kernel enables developers to focus on developing high-level communications functionality instead of low-level plumbing code. The realtime kernel imposes relatively low computational resource requirements so that realtime communications performance can be achieved using a wide range of computing devices and network connections that currently are available.