  The VOEvent standard provides a means of describing transient celestial
events in a machine-readable format. This is an essential step towards
analysing and, where appropriate, responding to the large volumes of transients
which will be detected by future large scale surveys. The VOEvent Transport
Protocol (VTP) defines a system by which VOEvents may be disseminated to the
community. We describe the design and implementation of Comet, a freely
available, open source implementation of VTP. We use Comet as a base to explore
the performance characteristics of the VTP system, in particular with reference
to meeting the requirements of future survey projects. We describe how, with
the aid of simple extensions to VTP, Comet can help users filter high-volume
streams of VOEvents to extract only those which are of relevance to particular
science cases. Based on these tests and on the experience of developing Comet,
we derive a number of recommendations for future refinements of the VTP
standard.
