How messages sent to clients are queued and how such queues can be manipulated by publishers

The Diffusion™ server maintains an outbound queue of messages for each client. Whenever a message is published to a topic, it is placed in the queue of each client subscribed to that topic as will any message sent explicitly to the client. Messages are sent to the client strictly in the order that they are enqueued.

Figure 1. The message queue

A publisher is able to enquire upon the details of a particular client's queue and even to change some aspects of the queue's behavior.