Welcome!

Industrial IoT Authors: Automic Blog, Liz McMillan, Elizabeth White, Stackify Blog, Yeshim Deniz

Related Topics: Java IoT, Industrial IoT, Microservices Expo, Microsoft Cloud, Machine Learning

Java IoT: Article

An Introduction to Client Latency

Speed as perceived by the end user is driven by multiple factors, including how fast results are returned

What is client latency?
Let's face it, users are impatient. They demand a blazingly fast experience and accept no substitutes. Google performed a study in 2010 which proved that when a site responds slowly, visitors spend less time there.

Speed as perceived by the end user is driven by multiple factors, including how fast results are returned and how long it takes a browser to display the
content.

So while the effects of poor performance is obvious, it makes one wonder about the relationship between client latency and the "perception of speed". After all, the user can trigger many state change events (page load, submit a form, interact with a visualization, etc) and all these events have an associated latency to the client. However, are certain types of latency more noticable to the user then others?

Let's look at all the different ways latency can creep in, throughout the ‘request-to-render' cycle.

Time To First Lag
The first place for potential client latency is the infamous Time To First Byte. From a user perspective, this is the worst kind of client latency, as it leaves the user with the dreaded "white screen of death".

WSoD

"White Screen of Death" in Google Chrome

Time To First Byte (TTFB) is the duration between a user making an HTTP request and first byte of the page being received by the browser. The following is a typical scenario for TTFB:

2 seconds to first byte ... but at least everything else is fast!

Two seconds to first byte ... but at least everything else is fast!

  • User enters a URL in browser and hits enter
  • The browser parses the URL
  • The browser performs a DNS lookup (Domain => IP address)
  • The browser opens a TCP connection and sends the HTTP Request
  • (Wait on the network)
  • The browser starts receiving the HTTP Response (first byte received)

As you can see, there are many places in this segment where latency can rear it's ugly head. The DNS lookup may fail, the web server may be under heavy load so it'squeueing requests, network channel congestion may be causing packet loss, or soft errors due to cosmic rays flipping bits.

This type of latency has negative effects on the user, as the user gets stuck looking at a loading/waiting animation. This becomes a true test of the user's patience, as an long TTFB can eventually lead the user to abandon the HTTP Request and close the browser tab.

Client Latency and the DOM
Now that the HTTP Response is pouring in, the browser engine can start doing what it does best...display content! But before the browser can render (or paint) content on the screen, there is still more work to be done!

NOTE: Not all browsers engines are created equal! Consult your local open source browser source code repository for detailed inner workings.

As the browser engine receives HTML, it begins constructing the HTML DOM tree. While parsing the HTML and building the DOM tree, the browser is looking for any
assets (or sub-resources) so it can initiate a download of their content.

So now that the HTTP Response has arrived, let's take a further look into the associated latency for both CSS and Javascript sub-resource and how it effects the user experience.

CSS
CSS related latency gives the user the impression of a "broken page". This comes in two forms, a "flash of unstyled content" (FOUC) where the page appears unstyled for a short period, then it flickers into the right design. However, if the stylesheet never loads, the DOM content will just remain unstyled. While this isn't ideal, its manageable because content is still available to the user but just in a degraded state.

Let's look at the effect of latency on styling and rendering the DOM.

browser_render

  • The browser is parsing the HTML in the HTTP Reponse
  • When the browser locates a link tag, it initiates a non-blocking download of the external CSS stylesheet
  • (Wait on network)
  • Once the download completes, the browser engine begins to parse the CSS
  • While parsing CSS, the browser engine is building all the CSS style rules and begins matching DOM elements to CSS styles
  • Once complete, the browser engine then applys the style rules with the DOM nodes by constructing a render tree
  • This builds a layout, which the browser then renders or paints to the screen

Latency in this segment is highly visible to the user, as it's the last hurdle to overcome before we can actually display content to the user. The first potential bottleneck is the placement of the stylesheet tag. We want the stylesheet to be downloaded as soon as possible, so we can progressively render the page. Thus, use your HEAD and Put stylesheets at the Top. The user-visible effect of not following this is a "flash of unstyled content" or a "white screen of death" (depending on the browser).

Our next stop on the latency express is the network. We always want to use an external stylesheet, however this requires an extra download. So we want this download to be fast, optimized for user location, and highly reliable. Well if you haven't been living under a rock, then you know to Use a Content Delivery Network (CDN). The user-visible effect of not following is slower loading of styled content, as your webserver has to handle extra requests to serve the assets (increased load) and this can be slower for users in geographically distant locations.

Finally, we have how you write your CSS as the last chokepoint. Inefficiently written CSS causes the browser to take longer to build a complete render tree, thus the user-visible effect is a slower loading page render. Fortunately, this is easily avoidable if you just Write efficient CSS.

Following CSS best practices will not only improve your user experience but also provide your users with the appearance that your pages are loading faster.

JavaScript
JavaScript related latency can have differing effects on the user experience. Clicking links that don't seem to do anything, stalled loading of the page, or a "laggy" feeling when scrolling through a page.

There are many places where client latency can appear with Javascript, so let's take ahighly simplified look at how the browser deals with Javascript.

  • The browser is parsing the HTML in the HTTP Reponse
  • When the browser locates a script tag, it initiates a blocking download of the external Javascript file
  • (Wait on network)
  • The browser parses the Javascript file
  • The browser executes the Javascript file
  • (The browser is no longer blocked)
  • Once complete, if the Javascript made changes to the DOM, this forces the construction of a new render tree.
  • This builds a layout, which the browser then renders or paints to the screen

You read that correct, the browser blocks when downloading Javascript files. This can be a real deal breaker for users and can cause a progressively loading page to stop dead in it's tracks. This blocking is a result of the potential use of document.write which can write HTML or Javascript to the document. This means the user has to wait patiently for the Javascript to download, parse, and run before any progress can be made with the page rendering. To avoid this type of client latency, you want to Put Scripts at the Bottom or use async or defer script tags.

All sub-resources have been downloaded, the page has been rendered, and now the user gets to actually do something. As the user navigates around your web application, Javascript is executing as your user triggers state changing events.

Inefficient or slow executing Javascript has the effect of reducing the browsers render/paint rate. This can cause "jank" which is defined as "problematic blocking of a software application's user interface due to slow operations." Without going into great detail, it's important to note that this type of latency is highly noticable to the user. Understanding how to properly use your developer tools is key in the battle against jank. Visit jankfree.org for more information.

Javascript that heavily manipulates the DOM is prone to reduced performance and increased client latency due to the triggering of excessive reflows. Excessive reflows will make the user's browser stutter, which is quite noticable. Everytime you change the DOM, this triggers reflows which forces the construction of a new render tree and then a re-paint of the screen. The DOM is slow, so it's best to take a batch approach when dealing with the DOM. This means, do all your DOM reads first and then do all your DOM writes second (and minimizing the amount of DOM writes).

// Bad!
var height = $('.container').height();
$('.container').height(height + 100);
var width = $('.container').width();
$('.container').width(width + 100);

// Good!
var height = $('.container').height();
var width = $('.container').width();
$('.container').height(height + 100);
$('.container').width(width + 100);

Finally, client latency can also appear when you make a XMLHttpRequest in Javascript. The user has to yet again wait on the network, however clever UX tricks (i.e. loading & transition animations) can help make this feel less noticeable to the user.

Conclusion
At the end of the day, the performance of your web application directly affects the user experience. Latency is a given in any networking application, so understanding how to mitigate its effects on your application will help improve performance and your overall user experience.

More Stories By Dan Riti

Dan Riti is a software developer with AppNeta with a passion for Python, JavaScript and music with a lot of bass.

@ThingsExpo Stories
WebRTC is great technology to build your own communication tools. It will be even more exciting experience it with advanced devices, such as a 360 Camera, 360 microphone, and a depth sensor camera. In his session at @ThingsExpo, Masashi Ganeko, a manager at INFOCOM Corporation, introduced two experimental projects from his team and what they learned from them. "Shotoku Tamago" uses the robot audition software HARK to track speakers in 360 video of a remote party. "Virtual Teleport" uses a multip...
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.
Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, discussed how from store operations and ...
In his session at 21st Cloud Expo, Carl J. Levine, Senior Technical Evangelist for NS1, will objectively discuss how DNS is used to solve Digital Transformation challenges in large SaaS applications, CDNs, AdTech platforms, and other demanding use cases. Carl J. Levine is the Senior Technical Evangelist for NS1. A veteran of the Internet Infrastructure space, he has over a decade of experience with startups, networking protocols and Internet infrastructure, combined with the unique ability to it...
Gemini is Yahoo’s native and search advertising platform. To ensure the quality of a complex distributed system that spans multiple products and components and across various desktop websites and mobile app and web experiences – both Yahoo owned and operated and third-party syndication (supply), with complex interaction with more than a billion users and numerous advertisers globally (demand) – it becomes imperative to automate a set of end-to-end tests 24x7 to detect bugs and regression. In th...
"Cloud Academy is an enterprise training platform for the cloud, specifically public clouds. We offer guided learning experiences on AWS, Azure, Google Cloud and all the surrounding methodologies and technologies that you need to know and your teams need to know in order to leverage the full benefits of the cloud," explained Alex Brower, VP of Marketing at Cloud Academy, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clar...
"There's plenty of bandwidth out there but it's never in the right place. So what Cedexis does is uses data to work out the best pathways to get data from the origin to the person who wants to get it," explained Simon Jones, Evangelist and Head of Marketing at Cedexis, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that Evatronix will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Evatronix SA offers comprehensive solutions in the design and implementation of electronic systems, in CAD / CAM deployment, and also is a designer and manufacturer of advanced 3D scanners for professional applications.
"MobiDev is a software development company and we do complex, custom software development for everybody from entrepreneurs to large enterprises," explained Alan Winters, U.S. Head of Business Development at MobiDev, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
It is of utmost importance for the future success of WebRTC to ensure that interoperability is operational between web browsers and any WebRTC-compliant client. To be guaranteed as operational and effective, interoperability must be tested extensively by establishing WebRTC data and media connections between different web browsers running on different devices and operating systems. In his session at WebRTC Summit at @ThingsExpo, Dr. Alex Gouaillard, CEO and Founder of CoSMo Software, presented ...
Leading companies, from the Global Fortune 500 to the smallest companies, are adopting hybrid cloud as the path to business advantage. Hybrid cloud depends on cloud services and on-premises infrastructure working in unison. Successful implementations require new levels of data mobility, enabled by an automated and seamless flow across on-premises and cloud resources. In his general session at 21st Cloud Expo, Greg Tevis, an IBM Storage Software Technical Strategist and Customer Solution Architec...
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, whic...
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
An increasing number of companies are creating products that combine data with analytical capabilities. Running interactive queries on Big Data requires complex architectures to store and query data effectively, typically involving data streams, an choosing efficient file format/database and multiple independent systems that are tied together through custom-engineered pipelines. In his session at @BigDataExpo at @ThingsExpo, Tomer Levi, a senior software engineer at Intel’s Advanced Analytics gr...
When talking IoT we often focus on the devices, the sensors, the hardware itself. The new smart appliances, the new smart or self-driving cars (which are amalgamations of many ‘things’). When we are looking at the world of IoT, we should take a step back, look at the big picture. What value are these devices providing? IoT is not about the devices, it’s about the data consumed and generated. The devices are tools, mechanisms, conduits. In his session at Internet of Things at Cloud Expo | DXWor...
Everything run by electricity will eventually be connected to the Internet. Get ahead of the Internet of Things revolution. In his session at @ThingsExpo, Akvelon expert and IoT industry leader Sergey Grebnov provided an educational dive into the world of managing your home, workplace and all the devices they contain with the power of machine-based AI and intelligent Bot services for a completely streamlined experience.
SYS-CON Events announced today that Synametrics Technologies will exhibit at SYS-CON's 22nd International Cloud Expo®, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Synametrics Technologies is a privately held company based in Plainsboro, New Jersey that has been providing solutions for the developer community since 1997. Based on the success of its initial product offerings such as WinSQL, Xeams, SynaMan and Syncrify, Synametrics continues to create and hone inn...
SYS-CON Events announced today that Google Cloud has been named “Keynote Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Companies come to Google Cloud to transform their businesses. Google Cloud’s comprehensive portfolio – from infrastructure to apps to devices – helps enterprises innovate faster, scale smarter, stay secure, and do more with data than ever before.