  The time domain community wants robust and reliable tools to enable
production of and subscription to community-endorsed event notification packets
(VOEvent). The VAO Transient Facility (VTF) is being designed to be the premier
brokering service for the community, both collecting and disseminating
observations about time-critical astronomical transients but also supporting
annotations and the application of intelligent machine-learning to those
observations. This distinguishes two types of activity associated with the
facility: core infrastructure and user services. In this paper, we will review
the prior art in both areas and describe the planned capabilities of the VTF.
In particular, we will focus on scalability and quality-of-service issues
required by the next generation of sky surveys, such as LSST and SKA.
