The Jixel CAP Router has been provided with an additional mechanism for the delivery of CAP messages: the open protocol “Pubsubhubbub”, designed by google, which can overcome some present limitations of the classical approach provided by the Atom / RSS protocols.
Content distribution via the standard Atom / RSS approach:
With this approach each user (subscriber) interested in the contents of a website subscribes to the feed on the publisher’s site (the publisher is the one who places the contents) and questions to the publisher at regular intervals to check for new content. The publisher verifies, whenever required by the subscribers, the presence or absence of new elements.
The disadvantage of this approach lies in the continuous requests from the subscriber to the publisher and therefore there is not an efficient communication.
Content distribution via the PubSubHubbub approach:
The PubSubHubbub protocol allows to overcome the limitations described above by including a broker (called a hub) between the subscriber and the publisher. This solution allows subscribers to receive new content without having to continually check for updates in the feed. In practice, the subscriber no longer interview the publisher to check for updates, but the publisher notifies subscribers when new content is published. Whenever the publisher releases new content contact the Hub, which in turn will send immediate updates to the subscriber.
Using this system, subscribers can receive updates in real time.
PubSubHubbub in the Jixel CAP Router:
The PubSubHubbub protocol has been introduced inside the Jixel suite to allow a more efficient delivery of CAP messages.
CAP Router has, therefore, a mechanism whereby each time a new message is posted within a feed the hub is warned, which in turn will send updates to another component (CAP Retriever) that acts as a subscriber.
The following diagram illustrates the structure and the communication flow between the Jixel components in a typical scenario of interoperability between organizations.
