|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
The consumption economy is here and so are cloud applications and solutions that offer more than subscription and flat fee models and at the same time are available on a pure consumption model, which not only reduces IT spend but also lowers infrastructure costs, and offers ease of use and availability. In their session at 15th Cloud Expo, Ermanno Bonifazi, CEO & Founder of Solgenia, and Ian Khan, Global Strategic Positioning & Brand Manager at Solgenia, discussed this shifting dynamic with an ...
May. 29, 2015 02:00 AM EDT Reads: 3,532
Due of the rise of Hadoop, many enterprises are now deploying their first small clusters of 10 to 20 servers. At this small scale, the complexity of operating the cluster looks and feels like general data center servers. It is not until the clusters scale, as they inevitably do, when the pain caused by the exponential complexity becomes apparent. We've seen this problem occur time and time again. In his session at Big Data Expo, Greg Bruno, Vice President of Engineering and co-founder of StackI...
May. 29, 2015 01:00 AM EDT Reads: 4,901
Once the decision has been made to move part or all of a workload to the cloud, a methodology for selecting that workload needs to be established. How do you move to the cloud? What does the discovery, assessment and planning look like? What workloads make sense? Which cloud model makes sense for each workload? What are the considerations for how to select the right cloud model? And how does that fit in with the overall IT transformation?
May. 29, 2015 12:00 AM EDT Reads: 4,709
You use an agile process; your goal is to make your organization more agile. But what about your data infrastructure? The truth is, today's databases are anything but agile - they are effectively static repositories that are cumbersome to work with, difficult to change, and cannot keep pace with application demands. Performance suffers as a result, and it takes far longer than it should to deliver new features and capabilities needed to make your organization competitive. As your application an...
May. 29, 2015 12:00 AM EDT Reads: 3,826
17th Cloud Expo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterprises a...
May. 28, 2015 11:15 PM EDT Reads: 2,796
The recent trends like cloud computing, social, mobile and Internet of Things are forcing enterprises to modernize in order to compete in the competitive globalized markets. However, enterprises are approaching newer technologies with a more silo-ed way, gaining only sub optimal benefits. The Modern Enterprise model is presented as a newer way to think of enterprise IT, which takes a more holistic approach to embracing modern technologies.
May. 28, 2015 11:00 PM EDT Reads: 6,427
SYS-CON Events announced today that SUSE, a pioneer in open source software, will exhibit at SYS-CON's DevOps Summit 2015 New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. SUSE provides reliable, interoperable Linux, cloud infrastructure and storage solutions that give enterprises greater control and flexibility. More than 20 years of engineering excellence, exceptional service and an unrivaled partner ecosystem power the products and support that help ...
May. 28, 2015 10:30 PM EDT Reads: 950
Move from reactive to proactive cloud management in a heterogeneous cloud infrastructure. In his session at 16th Cloud Expo, Manoj Khabe, Innovative Solution-Focused Transformation Leader at Vicom Computer Services, Inc., will show how to replace a help desk-centric approach with an ITIL-based service model and service-centric CMDB that’s tightly integrated with an event and incident management platform. Learn how to expand the scope of operations management to service management. He will al...
May. 28, 2015 10:00 PM EDT Reads: 2,080
There's no doubt that the Internet of Things is driving the next wave of innovation. Google has spent billions over the past few months vacuuming up companies that specialize in smart appliances and machine learning. Already, Philips light bulbs, Audi automobiles, and Samsung washers and dryers can communicate with and be controlled from mobile devices. To take advantage of the opportunities the Internet of Things brings to your business, you'll want to start preparing now.
May. 28, 2015 07:00 PM EDT Reads: 6,169
In a world of ever-accelerating business cycles and fast-changing client expectations, the cloud increasingly serves as a growth engine and a path to new business models. Dynamic clouds enable businesses to continuously reinvent themselves, adapting their business processes, their service and software delivery and their operations to achieve speed-to-market and quick response to customer feedback. As the cloud evolves, the industry has multiple competing cloud technologies, offering on-premises ...
May. 28, 2015 06:00 PM EDT Reads: 4,435
As the world moves from DevOps to NoOps, application deployment to the cloud ought to become a lot simpler. However, applications have been architected with a much tighter coupling than it needs to be which makes deployment in different environments and migration between them harder. The microservices architecture, which is the basis of many new age distributed systems such as OpenStack, Netflix and so on is at the heart of CloudFoundry – a complete developer-oriented Platform as a Service (PaaS...
May. 28, 2015 05:00 PM EDT Reads: 2,171
T-Mobile has been transforming the wireless industry with its “Uncarrier” initiatives. Today as T-Mobile’s IT organization works to transform itself in a like manner, technical foundations built over the last couple of years are now key to their drive for more Agile delivery practices. In his session at DevOps Summit, Martin Krienke, Sr Development Manager at T-Mobile, will discuss where they started their Continuous Delivery journey, where they are today, and where they are going in an effort ...
May. 28, 2015 04:45 PM EDT Reads: 2,370
SAP is delivering break-through innovation combined with fantastic user experience powered by the market-leading in-memory technology, SAP HANA. In his General Session at 15th Cloud Expo, Thorsten Leiduck, VP ISVs & Digital Commerce, SAP, discussed how SAP and partners provide cloud and hybrid cloud solutions as well as real-time Big Data offerings that help companies of all sizes and industries run better. SAP launched an application challenge to award the most innovative SAP HANA and SAP HANA...
May. 28, 2015 04:00 PM EDT Reads: 3,673
There is no question that the cloud is where businesses want to host data. Until recently hypervisor virtualization was the most widely used method in cloud computing. Recently virtual containers have been gaining in popularity, and for good reason. In the debate between virtual machines and containers, the latter have been seen as the new kid on the block – and like other emerging technology have had some initial shortcomings. However, the container space has evolved drastically since coming on...
May. 28, 2015 03:30 PM EDT Reads: 2,283
P2P RTC will impact the landscape of communications, shifting from traditional telephony style communications models to OTT (Over-The-Top) cloud assisted & PaaS (Platform as a Service) communication services. The P2P shift will impact many areas of our lives, from mobile communication, human interactive web services, RTC and telephony infrastructure, user federation, security and privacy implications, business costs, and scalability. In his session at @ThingsExpo, Robin Raymond, Chief Architect...
May. 28, 2015 03:00 PM EDT Reads: 4,734
The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long development cycles that produce software that is obsolete at launch. DevOps may be disruptive, but it is essential. The DevOps Summit at Cloud Expo – to be held June 3-5, 2015, at the Javits Center in New York City – will expand the DevOps community, enable a wide...
May. 28, 2015 03:00 PM EDT Reads: 2,886
The web app is Agile. The REST API is Agile. The testing and planning are Agile. But alas, Data infrastructures certainly are not. Once an application matures, changing the shape or indexing scheme of data often forces at best a top down planning exercise and at worst includes schema changes which force downtime. The time has come for a new approach that fundamentally advances the agility of distributed data infrastructures. Come learn about a new solution to the problems faced by software orga...
May. 28, 2015 02:56 PM EDT Reads: 891
Cloud Expo, Inc. has announced today that Andi Mann returns to DevOps Summit 2015 as Conference Chair. The 4th International DevOps Summit will take place on June 9-11, 2015, at the Javits Center in New York City. "DevOps is set to be one of the most profound disruptions to hit IT in decades," said Andi Mann. "It is a natural extension of cloud computing, and I have seen both firsthand and in independent research the fantastic results DevOps delivers. So I am excited to help the great team at ...
May. 28, 2015 02:00 PM EDT Reads: 2,445
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at Internet of @ThingsExpo, James Kirkland, Chief Ar...
May. 28, 2015 02:00 PM EDT Reads: 5,304
Container technology is sending shock waves through the world of cloud computing. Heralded as the 'next big thing,' containers provide software owners a consistent way to package their software and dependencies while infrastructure operators benefit from a standard way to deploy and run them. Containers present new challenges for tracking usage due to their dynamic nature. They can also be deployed to bare metal, virtual machines and various cloud platforms. How do software owners track the usag...
May. 28, 2015 01:30 PM EDT Reads: 1,259