All ØMQ connections should belong to some context, txZMQ wraps that into concept of factory that tracks all connections created and wraps context.
Factory could be used as an easy way to close all connections and clean up Twisted reactor.
:class:`ZmqConnection` isn't supposed to be used explicitly, it is base for different socket types.
These classes use PUB and SUB sockets from ØMQ. Special framing is implemented to support sending tag: tag and message are separated by zero byte and sent over as single message. This is related to the way PUB-SUB works with PGM (UDP multicast): multipart messages are sent as multiple datagrams and they get mixed together if several publishers exist in the same broadcast domain.