Reliable messaging

THE HTTP PROTOCOL is both the greatest strength and the Achilles' heel of the Web services movement. Yes, it's wonderful that SOAP (Simple Object Access Protocol) messages can go everywhere they are needed, but the HTTP, SOAP, WSDL (Web Services Description Language), and UDDI (Universal Description, Discovery, and Integration) stack doesn't address a slew of issues crucial to the effective deployment of Internet software, such as reliable messaging, single sign-on, and disconnected use.

Kenamea's Application Network is a suite of server-side and client-side technologies that collectively layer secure, transactional, and event-driven communications on top of HTTP, yielding a communications platform for reliable and highly interactive Internet applications.

The Application Network is powered by the Kenamea Message Switch -- a Java-based server that was first made available in July 2001 as a Kenamea-hosted service. And now in the new 1.2 release, the Application Network becomes a product you can deploy on Solaris or Windows 2000.

Opening the gates

The Message Switch is only the coordinating router in what is effectively a peer-to-peer network of clients and/or servers. Clients access the Switch by way of the Kenamea Desktop Connector, a gateway that opens an authenticated, persistent, and SSL (Secure Sockets Layer)-secured HTTP connection to the switch.

But the Desktop Connector is much more than just a gateway. It also guarantees that all messages sent to the network will be delivered exactly once. Because messages sent while disconnected are queued for later delivery, the Connector confers offline capability on applications built for the Kenamea platform. Moreover, because the Connector multiplexes all such applications onto a single connection, it conserves both client-side and switch-side resources. Finally, the Connector packages all this functionality for use by either thin-client Windows applications, such as those built on Internet Explorer-style DHTML (Dynamic HTML), or fat-client applications, such as those based on COM (Component Object Model).

A Kenamea DHTML Application typically runs in a Kenamea-supplied container that uses IE components, although it can also run directly in IE. Its elements are familiar to most Web developers: JavaScript and DHTML. At the core of every DHTML app are three JavaScript constructs that tie in to the messaging substrate. A SendMessage function delivers messages to the network, while an OnMessage function reacts to messages inbound from the network, which the Connector arranges to deliver as JavaScript events. Finally, a SubscribeToTopic function call registers the application to receive events from the Application Network.

To see how these pieces work together, you can download the Connector and try out the dispatcher example at http://www.kenamea.com . This app simulates a fleet of bike messengers. Inbound messages, which place packages in the delivery queue and report on the location and status of deliveries in progress, are mapped to a real-time display. In effect, the app's DOM (Document Object Model) is made directly sensitive to network events. The same app can inject events into the network by assigning idle couriers to waiting tasks. It's a dramatic illustration of what JavaScript and DHTML can do when unfettered by a stateless, client-pull, page-refresh model.