|By Gary Kaiser||
|July 28, 2014 07:00 AM EDT||
In Part V, we discussed processing delays caused by "slow" client and server nodes. In Part VI, we'll discuss the Nagle algorithm, a behavior that can have a devastating impact on performance and, in many ways, appear to be a processing delay.
Common TCP ACK Timing
Beyond being important for (reasonably) accurate packet flow diagrams, understanding "normal" TCP ACK timing can help in the effective diagnosis of certain types of performance problems. These include those introduced by the Nagle algorithm, which we will discuss here, and application windowing, to be discussed in Part VII.
A slightly simplified but useful rule of thumb is as follows:
A receiving node will:
- Acknowledge every second packet immediately
- Acknowledge a single packet if the Delayed ACK timer expires before a second packet arrives
The Delayed ACK timer typically defaults to 200 milliseconds, at least on Microsoft platforms.
While this behavior is quite common, you may encounter differences; for example, changing the ACK frequency to every packet is an approach to circumventing certain problems, while shorter Delayed ACK timers may be observed in non-Microsoft environments.
ACK every second packet, or a single packet after the Delayed ACK timer expires
The Nagle Algorithm
The Nagle algorithm was designed to help reduce network overhead by delaying the transmission of a small packet (i.e., <MSS) until all previously transmitted packets have been acknowledged. The goal was to prevent a node from transmitting many small packets if the application delivers data to the socket rather slowly. The usefulness of the algorithm and the frequency with which it is applied have both diminished dramatically; however, you may still encounter it, as the option still exists in most environments.
To begin to understand the impact of the Nagle algorithm, consider a request or reply flow; chances are, the size of the payload in the flow is not an exact multiple of the MSS. Therefore, the last packet of the flow will be smaller than the MSS. With Nagle enabled, this last packet will not be transmitted until the previous (penultimate) packet has been acknowledged. In the best case, the penultimate packet represents an even-numbered packet in the flow, triggering an immediate acknowledgement from the receiver which in turn "releases" the final small packet. In this case, the Nagle penalty is equal to one network round-trip for the entire flow. Should the penultimate packet be an odd-numbered packet, it will not be acknowledged by the receiver until the Delayed ACK timer expires; the penalty becomes one network round-trip plus approximately 200 milliseconds.
The HTTP reply includes two data packets; the last packet is not sent until the earlier packet has been acknowledged. The Delayed ACK timer adds about 200 milliseconds to the transmission of the reply.
For more network tips click here for the full article
Cloud computing delivers on-demand resources that provide businesses with flexibility and cost-savings. The challenge in moving workloads to the cloud has been the cost and complexity of ensuring the initial and ongoing security and regulatory (PCI, HIPAA, FFIEC) compliance across private and public clouds. Manual security compliance is slow, prone to human error, and represents over 50% of the cost of managing cloud applications. Determining how to automate cloud security compliance is critical...
Nov. 30, 2015 12:00 AM EST Reads: 449
Culture is the most important ingredient of DevOps. The challenge for most organizations is defining and communicating a vision of beneficial DevOps culture for their organizations, and then facilitating the changes needed to achieve that. Often this comes down to an ability to provide true leadership. As a CIO, are your direct reports IT managers or are they IT leaders? The hard truth is that many IT managers have risen through the ranks based on their technical skills, not their leadership ab...
Nov. 30, 2015 12:00 AM EST Reads: 418
As organizations shift towards IT-as-a-service models, the need for managing & protecting data residing across physical, virtual, and now cloud environments grows with it. CommVault can ensure protection & E-Discovery of your data - whether in a private cloud, a Service Provider delivered public cloud, or a hybrid cloud environment – across the heterogeneous enterprise.
Nov. 29, 2015 06:00 PM EST Reads: 235
Today air travel is a minefield of delays, hassles and customer disappointment. Airlines struggle to revitalize the experience. GE and M2Mi will demonstrate practical examples of how IoT solutions are helping airlines bring back personalization, reduce trip time and improve reliability. In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect with GE, and Dr. Sarah Cooper, M2Mi’s VP Business Development and Engineering, explored the IoT cloud-based platform technologies driving t...
Nov. 29, 2015 06:00 PM EST Reads: 443
In his General Session at DevOps Summit, Asaf Yigal, Co-Founder & VP of Product at Logz.io, explored the value of Kibana 4 for log analysis and provided a hands-on tutorial on how to set up Kibana 4 and get the most out of Apache log files. He examined three use cases: IT operations, business intelligence, and security and compliance. Asaf Yigal is co-founder and VP of Product at log analytics software company Logz.io. In the past, he was co-founder of social-trading platform Currensee, which...
Nov. 29, 2015 04:00 PM EST Reads: 255
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...
Nov. 29, 2015 02:00 PM EST Reads: 485
Just over a week ago I received a long and loud sustained applause for a presentation I delivered at this year’s Cloud Expo in Santa Clara. I was extremely pleased with the turnout and had some very good conversations with many of the attendees. Over the next few days I had many more meaningful conversations and was not only happy with the results but also learned a few new things. Here is everything I learned in those three days distilled into three short points.
Nov. 29, 2015 01:00 PM EST Reads: 357
DevOps is about increasing efficiency, but nothing is more inefficient than building the same application twice. However, this is a routine occurrence with enterprise applications that need both a rich desktop web interface and strong mobile support. With recent technological advances from Isomorphic Software and others, rich desktop and tuned mobile experiences can now be created with a single codebase – without compromising functionality, performance or usability. In his session at DevOps Su...
Nov. 29, 2015 12:45 PM EST Reads: 421
As organizations realize the scope of the Internet of Things, gaining key insights from Big Data, through the use of advanced analytics, becomes crucial. However, IoT also creates the need for petabyte scale storage of data from millions of devices. A new type of Storage is required which seamlessly integrates robust data analytics with massive scale. These storage systems will act as “smart systems” provide in-place analytics that speed discovery and enable businesses to quickly derive meaningf...
Nov. 29, 2015 12:30 PM EST Reads: 427
In his keynote at @ThingsExpo, Chris Matthieu, Director of IoT Engineering at Citrix and co-founder and CTO of Octoblu, focused on building an IoT platform and company. He provided a behind-the-scenes look at Octoblu’s platform, business, and pivots along the way (including the Citrix acquisition of Octoblu).
Nov. 29, 2015 12:00 PM EST Reads: 528
In his General Session at 17th Cloud Expo, Bruce Swann, Senior Product Marketing Manager for Adobe Campaign, explored the key ingredients of cross-channel marketing in a digital world. Learn how the Adobe Marketing Cloud can help marketers embrace opportunities for personalized, relevant and real-time customer engagement across offline (direct mail, point of sale, call center) and digital (email, website, SMS, mobile apps, social networks, connected objects).
Nov. 29, 2015 11:45 AM EST Reads: 329
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 da...
Nov. 29, 2015 11:30 AM EST Reads: 276
In recent years, at least 40% of companies using cloud applications have experienced data loss. One of the best prevention against cloud data loss is backing up your cloud data. In his General Session at 17th Cloud Expo, Sam McIntyre, Partner Enablement Specialist at eFolder, presented how organizations can use eFolder Cloudfinder to automate backups of cloud application data. He also demonstrated how easy it is to search and restore cloud application data using Cloudfinder.
Nov. 29, 2015 10:00 AM EST Reads: 204
The Internet of Everything is re-shaping technology trends–moving away from “request/response” architecture to an “always-on” Streaming Web where data is in constant motion and secure, reliable communication is an absolute necessity. As more and more THINGS go online, the challenges that developers will need to address will only increase exponentially. In his session at @ThingsExpo, Todd Greene, Founder & CEO of PubNub, exploreed the current state of IoT connectivity and review key trends and t...
Nov. 29, 2015 09:45 AM EST Reads: 454
We all know that data growth is exploding and storage budgets are shrinking. Instead of showing you charts on about how much data there is, in his General Session at 17th Cloud Expo, Scott Cleland, Senior Director of Product Marketing at HGST, showed how to capture all of your data in one place. After you have your data under control, you can then analyze it in one place, saving time and resources.
Nov. 29, 2015 08:45 AM EST Reads: 232
With all the incredible momentum behind the Internet of Things (IoT) industry, it is easy to forget that not a single CEO wakes up and wonders if “my IoT is broken.” What they wonder is if they are making the right decisions to do all they can to increase revenue, decrease costs, and improve customer experience – effectively the same challenges they have always had in growing their business. The exciting thing about the IoT industry is now these decisions can be better, faster, and smarter. Now ...
Nov. 29, 2015 08:00 AM EST Reads: 282
Discussions of cloud computing have evolved in recent years from a focus on specific types of cloud, to a world of hybrid cloud, and to a world dominated by the APIs that make today's multi-cloud environments and hybrid clouds possible. In this Power Panel at 17th Cloud Expo, moderated by Conference Chair Roger Strukhoff, panelists addressed the importance of customers being able to use the specific technologies they need, through environments and ecosystems that expose their APIs to make true ...
Nov. 29, 2015 06:00 AM EST Reads: 559
Too often with compelling new technologies market participants become overly enamored with that attractiveness of the technology and neglect underlying business drivers. This tendency, what some call the “newest shiny object syndrome” is understandable given that virtually all of us are heavily engaged in technology. But it is also mistaken. Without concrete business cases driving its deployment, IoT, like many other technologies before it, will fade into obscurity.
Nov. 29, 2015 06:00 AM EST Reads: 377
Microservices are a very exciting architectural approach that many organizations are looking to as a way to accelerate innovation. Microservices promise to allow teams to move away from monolithic "ball of mud" systems, but the reality is that, in the vast majority of organizations, different projects and technologies will continue to be developed at different speeds. How to handle the dependencies between these disparate systems with different iteration cycles? Consider the "canoncial problem"...
Nov. 29, 2015 05:00 AM EST Reads: 462
The Internet of Things is clearly many things: data collection and analytics, wearables, Smart Grids and Smart Cities, the Industrial Internet, and more. Cool platforms like Arduino, Raspberry Pi, Intel's Galileo and Edison, and a diverse world of sensors are making the IoT a great toy box for developers in all these areas. In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists discussed what things are the most important, which will have the most profound...
Nov. 29, 2015 04:30 AM EST Reads: 488