Click here to close now.


Java IoT Authors: Liz McMillan, AppDynamics Blog, Pat Romanski, Elizabeth White, Ed Featherston

Related Topics: IoT User Interface

IoT User Interface: Article

Enterprise Comet: Awaken the Grizzly!

The real deal

There's a common misconception among many end users, consumers, and developers that AJAX is the ultimate solution for the Web and that it can provide all the same functionality as a rich desktop solution. Sure, AJAX can cover most of our expectations for a rich client, mimicking functionality provided by a desktop application, but there's still one area that has yet to be fully integrated ­ scalable server-initiated message delivery.

With server-initiated message delivery, all end users of a particular application are simultaneously notified of any changes to the application state, e.g., at the stock exchange a stock is dropping fast and the trading application has to inform all traders about the sudden change in price.

Server-Initiated Message Delivery
Let's use the trading application as an example for server-initiated message delivery. Each broker has his own preferences in stocks and bonds and requires instant notification of changes in the market. A desktop client for a distributed enterprise application typically registers interest in specific kinds of server messages so the server can notify the desktop client when they occur. This lets the desktop application efficiently use the network on a need-to-know basis instead of having the client actively ask for information.

This approach won't work for a traditional Web-based AJAX application since the server can't initiate a direct connection to the browser because of browser security, firewalls, and Web proxies.

Sure, it's possible with AJAX to "notify" a Web client that a change has occurred on the server using a technique called "polling." By creating a Web application that polls every now and then the end user believes that he's been notified by the server, when in fact it's repeatedly asking for updates like any child asking for candy ­ Can I get it now? Can I get it now? Can I get it now? You get the picture.

Of course, this impacts network bandwidth since there's traffic for each polling request even when no updates are available from the server. We need a way for Web clients to register interest in certain types of messages and then let the server initiate delivery of those messages, pushing them to each browser.

There's a Twist
OK, OK, OK, there is a twist ­ you can't actually "push" messages to a Web-based AJAX application unless you maintain an open connection from the client to the server. However, a thread is kept alive on the server for each open connection so messages can be delivered to the browser immediately.

The fact that you'd even try to maintain an open connection per user to a server would have heads rolling down the corridors in most IT departments. Just imagine thousands, or even hundreds of thousands of connections, using the thread and process pooling models provided by most Web Servers today, keeping each thread alive on the server just to be able to send a message to the client ­ it doesn't scale! Let's come back to that one later.

HTTP Connection Limitations
Today most frameworks leveraging AJAX are using the XMLHttpRequest object, which allocates an HTTP connection for the duration of the request. The HTTP 1.1 specification recommends that browsers support a maximum of two open connections to the hosting server. This presents a problem for highly interactive AJAX Web applications, especially on Microsoft Internet Explorer, which enforces this recommendation.

If there are more than two AJAX frameworks or components using the XMLHttpRequest on the same Web page then there will probably be contention for the two open connections, causing requests to queue. The result will be blocked and ineffective communication, defeating the main purpose of having AJAX on the Web page. There's a need to share server communications over two HTTP connections at most.

Next-Generation Web Communication
The main reason a Web server allocates one thread per connection is because it expects the request to be highly active and short-lived. However, maintaining an open connection to the server is extremely long-lived and activity is mostly dormant. We also need a way to meaningfully share server communications to address the browser connection limit. Thankfully, there are several projects in process addressing the limitations of traditional AJAX Web applications. Let's have a look at some of these projects.

Comet - The Never-Ending Request
First we need a way to create message-driven Web applications that require the server to notify the client about server-side events. This is where Comet comes in as described by Wikipedia:
Comet is a programming technique that enables Web servers to send data to the client without having any need for the client to request it.

Comet provides the means for the server to initiate a response to a client request, and later send a message to that client using the same response ­ for example, in the browser a message will "just" appear. Comet also provides clients with a way to register interest in specific types of messages. When the server publishes a message, it's delivered only to clients that previously registered interest in that kind of message.

Comet doesn't solve everything; in fact it creates some new problems. Using Comet means lots of outstanding requests, ideally one per client, and introduces similar scalability issues at the server as the AJAX polling technique. Keeping a separate thread allocated for each open request will exhaust the server's resources, so for this model to work properly, the Web server has to handle multiple requests without allocating one thread per request.

Asynchronous Request Processing
The idea behind Asynchronous Request Processing (ARP) is to manage incoming servlet requests asynchronously. Rather than committing a separate Java thread to synchronously process each servlet request, a single thread leverages Java NIO to detect when new information needs to be written to the response of any outstanding request. This technique provides a huge scalability win for the Comet use case, giving excellent performance even when there are a large number of outstanding, mostly dormant, requests at the server.

Although there's no standard defined for ARP several teams and projects are providing ARP solutions, such as Jetty Continuations and Grizzly. We take our hats off to these visionary teams providing everyday developers with ARP and Comet solutions.

Note: There's hope that ARP will be standard in the Servlet 3.0 and Java EE 6 specifications.

The Comet Messaging Protocol
With Comet and ARP we now have the means to build message-driven Web applications but, as mentioned earlier, W3C recommends at most two active connections from the browser to the Web server at any one time. Therefore, we'd prefer to have a single active connection being used for Comet notifications, leaving the other connection free to download images, CSS, and JavaScript or communicate with the server. This requires a way to manage multiple logical channels of information over a single shared Comet notification response.

More Stories By Kaazing Blog

Kaazing is helping define the future of the event-driven enterprise by accelerating the Web for the Internet of Things.

More Stories By John Fallows

John brings to Kaazing his 17 years’ experience in technology development and software design, and is considered a pioneer in the field of rich and highly interactive user interfaces. As CTO he formulates Kaazing Corporation’s vision of enabling mobile users, marketplaces and machines to connect and communicate in real-time, more reliably and at unprecedented scale. He defines the architecture of the Kaazing product suite and oversees its development. Prior to co-founding Kaazing, John served as Architect for Brane Corporation, a startup company based in Redwood City, California. Before joining Brane, he was a Consulting Member of Technical Staff for Server Technologies at Oracle Corporation. During his last five years at Oracle, he focused on designing, developing, and evolving Oracle ADF Faces to fully integrate Ajax technologies. Originally from Northern Ireland, he received his MA in Computer Science from Cambridge University in the United Kingdom and has written several articles for leading IT magazines such as Java Developer’s Journal, AjaxWorld Magazine, and JavaMagazine (DE), and is a popular speaker at international conferences. He is co-author of the bestselling book Pro JSF and Ajax: Building Rich Internet Components (Apress).

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.

@ThingsExpo Stories
The buzz continues for cloud, data analytics and the Internet of Things (IoT) and their collective impact across all industries. But a new conversation is emerging - how do companies use industry disruption and technology enablers to lead in markets undergoing change, uncertainty and ambiguity? Organizations of all sizes need to evolve and transform, often under massive pressure, as industry lines blur and merge and traditional business models are assaulted and turned upside down. In this new data-driven world, marketplaces reign supreme while interoperability, APIs and applications deliver un...
The Internet of Things (IoT) is growing rapidly by extending current technologies, products and networks. By 2020, Cisco estimates there will be 50 billion connected devices. Gartner has forecast revenues of over $300 billion, just to IoT suppliers. Now is the time to figure out how you’ll make money – not just create innovative products. With hundreds of new products and companies jumping into the IoT fray every month, there’s no shortage of innovation. Despite this, McKinsey/VisionMobile data shows "less than 10 percent of IoT developers are making enough to support a reasonably sized team....
There are so many tools and techniques for data analytics that even for a data scientist the choices, possible systems, and even the types of data can be daunting. In his session at @ThingsExpo, Chris Harrold, Global CTO for Big Data Solutions for EMC Corporation, will show how to perform a simple, but meaningful analysis of social sentiment data using freely available tools that take only minutes to download and install. Participants will get the download information, scripts, and complete end-to-end walkthrough of the analysis from start to finish. Participants will also be given the pract...
The IoT market is on track to hit $7.1 trillion in 2020. The reality is that only a handful of companies are ready for this massive demand. There are a lot of barriers, paint points, traps, and hidden roadblocks. How can we deal with these issues and challenges? The paradigm has changed. Old-style ad-hoc trial-and-error ways will certainly lead you to the dead end. What is mandatory is an overarching and adaptive approach to effectively handle the rapid changes and exponential growth.
Today’s connected world is moving from devices towards things, what this means is that by using increasingly low cost sensors embedded in devices we can create many new use cases. These span across use cases in cities, vehicles, home, offices, factories, retail environments, worksites, health, logistics, and health. These use cases rely on ubiquitous connectivity and generate massive amounts of data at scale. These technologies enable new business opportunities, ways to optimize and automate, along with new ways to engage with users.
Internet of Things (IoT) will be a hybrid ecosystem of diverse devices and sensors collaborating with operational and enterprise systems to create the next big application. In their session at @ThingsExpo, Bramh Gupta, founder and CEO of, and Fred Yatzeck, principal architect leading product development at, discussed how choosing the right middleware and integration strategy from the get-go will enable IoT solution developers to adapt and grow with the industry, while at the same time reduce Time to Market (TTM) by using plug and play capabilities offered by a robust IoT ...
Mobile messaging has been a popular communication channel for more than 20 years. Finnish engineer Matti Makkonen invented the idea for SMS (Short Message Service) in 1984, making his vision a reality on December 3, 1992 by sending the first message ("Happy Christmas") from a PC to a cell phone. Since then, the technology has evolved immensely, from both a technology standpoint, and in our everyday uses for it. Originally used for person-to-person (P2P) communication, i.e., Sally sends a text message to Betty – mobile messaging now offers tremendous value to businesses for customer and empl...
Can call centers hang up the phones for good? Intuitive Solutions did. WebRTC enabled this contact center provider to eliminate antiquated telephony and desktop phone infrastructure with a pure web-based solution, allowing them to expand beyond brick-and-mortar confines to a home-based agent model. It also ensured scalability and better service for customers, including MUY! Companies, one of the country's largest franchise restaurant companies with 232 Pizza Hut locations. This is one example of WebRTC adoption today, but the potential is limitless when powered by IoT.
You have your devices and your data, but what about the rest of your Internet of Things story? Two popular classes of technologies that nicely handle the Big Data analytics for Internet of Things are Apache Hadoop and NoSQL. Hadoop is designed for parallelizing analytical work across many servers and is ideal for the massive data volumes you create with IoT devices. NoSQL databases such as Apache HBase are ideal for storing and retrieving IoT data as “time series data.”
Clearly the way forward is to move to cloud be it bare metal, VMs or containers. One aspect of the current public clouds that is slowing this cloud migration is cloud lock-in. Every cloud vendor is trying to make it very difficult to move out once a customer has chosen their cloud. In his session at 17th Cloud Expo, Naveen Nimmu, CEO of Clouber, Inc., will advocate that making the inter-cloud migration as simple as changing airlines would help the entire industry to quickly adopt the cloud without worrying about any lock-in fears. In fact by having standard APIs for IaaS would help PaaS expl...
SYS-CON Events announced today that ProfitBricks, the provider of painless cloud infrastructure, will exhibit at SYS-CON's 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. ProfitBricks is the IaaS provider that offers a painless cloud experience for all IT users, with no learning curve. ProfitBricks boasts flexible cloud servers and networking, an integrated Data Center Designer tool for visual control over the cloud and the best price/performance value available. ProfitBricks was named one of the coolest Clo...
Organizations already struggle with the simple collection of data resulting from the proliferation of IoT, lacking the right infrastructure to manage it. They can't only rely on the cloud to collect and utilize this data because many applications still require dedicated infrastructure for security, redundancy, performance, etc. In his session at 17th Cloud Expo, Emil Sayegh, CEO of Codero Hosting, will discuss how in order to resolve the inherent issues, companies need to combine dedicated and cloud solutions through hybrid hosting – a sustainable solution for the data required to manage I...
NHK, Japan Broadcasting, will feature the upcoming @ThingsExpo Silicon Valley in a special 'Internet of Things' and smart technology documentary that will be filmed on the expo floor between November 3 to 5, 2015, in Santa Clara. NHK is the sole public TV network in Japan equivalent to the BBC in the UK and the largest in Asia with many award-winning science and technology programs. Japanese TV is producing a documentary about IoT and Smart technology and will be covering @ThingsExpo Silicon Valley. The program, to be aired during the peak viewership season of the year, will have a major impac...
Apps and devices shouldn't stop working when there's limited or no network connectivity. Learn how to bring data stored in a cloud database to the edge of the network (and back again) whenever an Internet connection is available. In his session at 17th Cloud Expo, Bradley Holt, Developer Advocate at IBM Cloud Data Services, will demonstrate techniques for replicating cloud databases with devices in order to build offline-first mobile or Internet of Things (IoT) apps that can provide a better, faster user experience, both offline and online. The focus of this talk will be on IBM Cloudant, Apa...
WebRTC is about the data channel as much as about video and audio conferencing. However, basically all commercial WebRTC applications have been built with a focus on audio and video. The handling of “data” has been limited to text chat and file download – all other data sharing seems to end with screensharing. What is holding back a more intensive use of peer-to-peer data? In her session at @ThingsExpo, Dr Silvia Pfeiffer, WebRTC Applications Team Lead at National ICT Australia, will look at different existing uses of peer-to-peer data sharing and how it can become useful in a live session to...
As a company adopts a DevOps approach to software development, what are key things that both the Dev and Ops side of the business must keep in mind to ensure effective continuous delivery? In his session at DevOps Summit, Mark Hydar, Head of DevOps, Ericsson TV Platforms, will share best practices and provide helpful tips for Ops teams to adopt an open line of communication with the development side of the house to ensure success between the two sides.
SYS-CON Events announced today that IBM Cloud Data Services has been named “Bronze Sponsor” of SYS-CON's 17th Cloud Expo, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. IBM Cloud Data Services offers a portfolio of integrated, best-of-breed cloud data services for developers focused on mobile computing and analytics use cases.
"Matrix is an ambitious open standard and implementation that's set up to break down the fragmentation problems that exist in IP messaging and VoIP communication," explained John Woolf, Technical Evangelist at Matrix, in this interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
WebRTC has had a real tough three or four years, and so have those working with it. Only a few short years ago, the development world were excited about WebRTC and proclaiming how awesome it was. You might have played with the technology a couple of years ago, only to find the extra infrastructure requirements were painful to implement and poorly documented. This probably left a bitter taste in your mouth, especially when things went wrong.
Nowadays, a large number of sensors and devices are connected to the network. Leading-edge IoT technologies integrate various types of sensor data to create a new value for several business decision scenarios. The transparent cloud is a model of a new IoT emergence service platform. Many service providers store and access various types of sensor data in order to create and find out new business values by integrating such data.