|By Gary Kaiser||
|July 9, 2014 07:45 AM EDT||
When we think of application performance problems that are network-related, we often immediately think of bandwidth and congestion as likely culprits; faster speeds and less traffic will solve everything, right? This is reminiscent of recent ISP wars; which is better, DSL or cable modems? Cable modem proponents touted the higher bandwidth while DSL proponents warned of the dangers of sharing the network with your potentially bandwidth-hogging neighbors. In this blog entry, we'll examine these two closely-related constraints, beginning the series of performance analyses using the framework we introduced in Part I. I'll use graphics from Compuware's application-centric protocol analyzer - Transaction Trace - as illustrations.
We define bandwidth delay as the serialization delay encountered as bits are clocked out onto the network medium. Most important for performance analysis is what we refer to as the "bottleneck bandwidth" - the speed of the link at its slowest point - as this will be the primary influencer on the packet arrival rate at the destination. Each packet incurs the serialization delay dictated by the link speed; for example, at 4Mbps, a 1500 byte packet takes approximately 3 milliseconds to be serialized. Extending this bandwidth calculation to an entire operation is relatively straightforward. We observe (on the wire) the number of bytes sent or received and multiply that by 8 bits, then divide by the bottleneck link speed, understanding that asymmetric links may have different upstream and downstream speeds.
Bandwidth effect = [ [# bytes sent or received] x [8 bits] ]/ [Bottleneck link speed]
For example, we can calculate the bandwidth effect for an operation that sends 100KB and receives 1024KB on a 2048Kbps link:
- Upstream effect: [100,000 * 8] / 2,048,000] = 390 milliseconds
- Downstream effect: [1,024,000 *8] / 2,048,000] = 4000 milliseconds
For better precision, you should account for frame header size differences between the packet capture medium - Ethernet, likely - and the WAN link; this difference might be as much as 8 or 10 bytes per packet.
Bandwidth constraints impact only the data transfer periods within an operation - the request and reply flows. Each flow also incurs (at a minimum) additional delay due to network latency, as the first bit traverses the network from sender to receiver; TCP flow control or other factors may introduce further delays. (As an operation's chattiness increases, its sensitivity to network latency increases and the overall impact of bandwidth tends to decrease, becoming overshadowed by latency.)
Transaction Trace Illustration: Bandwidth
One way to frame the question is "does the operation use all of the available bandwidth?" The simplest way to visualize this is to graph throughput in each direction, comparing uni-directional throughput with the link's measured bandwidth. If the answer is yes, then the operation bottleneck is bandwidth; if the answer is no, then there is some other constraint limiting performance. (This doesn't mean that bandwidth isn't a significant, or even the dominant, constraint; it simply means that there are other factors that prevent the operation from reaching the bandwidth limitation. The formula we used to calculate the impact of bandwidth still applies as a definition of the contribution of bandwidth to the overall operation time.)
This FTP transfer is frequently limited by the 10Mbps available bandwidth.
Networks are generally shared resources; when there are multiple connections on a link, TCP flow control will prevent a single flow from using all of the available bandwidth as it detects and adjusts for congestion. We will evaluate the impact of congestion next, but fundamentally, the diagnosis is the same; bandwidth constrains throughput.
Congestion occurs when data arrives at a network interface at a rate faster than the media can service; when this occurs, packets must be placed in an output queue, waiting until earlier packets have been serviced. These queue delays add to the end-to-end network delay, with a potentially significant effect on both chatty and non-chatty operations. (Chatty operations will be impacted due to the increase in round-trip delay, while non-chatty operations may be impacted by TCP flow control and congestion avoidance algorithms.)
For a given flow, congestion initially reduces the rate of TCP slow-start's ramp by slowing increases to the sender's Congestion Window (CWD); it also adds to the delay component of the Bandwidth Delay Product (BDP), increasing the likelihood of exhausting the receiver's TCP window. (We'll discuss TCP slow-start as well as the BDP later in this series.)
As congestion becomes more severe, the queue in one of the path's routers may become full. As packets arrive exceeding the queue's storage capacity, some packets must be discarded. Routers employ various algorithms to determine which packets should be dropped, perhaps attempting to distribute congestion's impact among multiple connections, or to more significantly impact lower-priority traffic. When TCP detects these dropped packets (by a triple-duplicate ACK, for example), congestion is the assumed cause. As we will discuss in more depth in an upcoming blog entry, packet loss causes the sending TCP to reduce its Congestion Window by 50%, after which slow-start begins to ramp up again in a relatively conservative congestion avoidance phase.
For more on congestion, and for further insight, click here for the full article.
Dyn solutions are at the core of Internet Performance. Through traffic management, message management and performance assurance, Dyn is connecting people through the Internet and ensuring information gets where it needs to go, faster and more reliably than ever before. Founded in 2001 at WPI, Dyn’s global presence services more than four million enterprise, small business and personal customers.
Oct. 31, 2014 01:00 PM EDT Reads: 2,022
SimpleECM is the only platform to offer a powerful combination of enterprise content management (ECM) services, capture solutions, and third-party business services providing simplified integrations and workflow development for solution providers. SimpleECM is opening the market to businesses of all sizes by reinventing the delivery of ECM services. Our APIs make the development of ECM services simple with the use of familiar technologies for a frictionless integration directly into web applicat...
Oct. 31, 2014 11:00 AM EDT Reads: 2,002
Samsung VP Jacopo Lenzi, who headed the company's recent SmartThings acquisition under the auspices of Samsung's Open Innovaction Center (OIC), answered a few questions we had about the deal. This interview was in conjunction with our interview with SmartThings CEO Alex Hawkinson. IoT Journal: SmartThings was developed in an open, standards-agnostic platform, and will now be part of Samsung's Open Innovation Center. Can you elaborate on your commitment to keep the platform open? Jacopo Lenzi: S...
Oct. 31, 2014 09:00 AM EDT Reads: 3,393
The Internet of Things will greatly expand the opportunities for data collection and new business models driven off of that data. In her session at Internet of @ThingsExpo, Esmeralda Swartz, CMO of MetraTech, will discuss how for this to be effective you not only need to have infrastructure and operational models capable of utilizing this new phenomenon, but increasingly service providers will need to convince a skeptical public to participate. Get ready to show them the money! Speaker Bio: ...
Oct. 31, 2014 09:00 AM EDT Reads: 2,350
Things are being built upon cloud foundations to transform organizations. This CEO Power Panel at 15th Cloud Expo, moderated by Roger Strukhoff, Cloud Expo and @ThingsExpo conference chair, will address the big issues involving these technologies and, more important, the results they will achieve. How important are public, private, and hybrid cloud to the enterprise? How does one define Big Data? And how is the IoT tying all this together?
Oct. 31, 2014 08:45 AM EDT Reads: 2,017
The only place to be June 9-11 is Cloud Expo & @ThingsExpo 2015 East at the Javits Center in New York City. Join us there as delegates from all over the world come to listen to and engage with speakers & sponsors from the leading Cloud Computing, IoT & Big Data companies. Cloud Expo & @ThingsExpo are the leading events covering the booming market of Cloud Computing, IoT & Big Data for the enterprise. Speakers from all over the world will be hand-picked for their ability to explore the economic...
Oct. 30, 2014 05:30 PM EDT Reads: 1,495
SYS-CON Events announced today that Cloudian, Inc., the leading provider of hybrid cloud storage solutions, has been named “Bronze Sponsor” of SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Cloudian is a Foster City, Calif.-based software company specializing in cloud storage. Cloudian HyperStore® is an S3-compatible cloud object storage platform that enables service providers and enterprises to bui...
Oct. 30, 2014 04:45 PM EDT Reads: 1,927
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, will discuss 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 ...
Oct. 30, 2014 09:00 AM EDT Reads: 2,103
SYS-CON Events announced today that O'Reilly Media has been named “Media Sponsor” of SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. O'Reilly Media spreads the knowledge of innovators through its books, online services, magazines, and conferences. Since 1978, O'Reilly Media has been a chronicler and catalyst of cutting-edge development, homing in on the technology trends that really matter and spurri...
Oct. 29, 2014 01:00 PM EDT Reads: 1,661
The Internet of Things (IoT) is going to require a new way of thinking and of developing software for speed, security and innovation. This requires IT leaders to balance business as usual while anticipating for the next market and technology trends. Cloud provides the right IT asset portfolio to help today’s IT leaders manage the old and prepare for the new. Today the cloud conversation is evolving from private and public to hybrid. This session will provide use cases and insights to reinforce t...
Oct. 29, 2014 09:00 AM EDT Reads: 2,108
Samsung promises to be one of the 800-pound gorillas of the IoT, if its success in recent years with Android devices and other consumer electronics is any guide. Showing its willingness to be a big IoT player, the company recently acquired SmartThings, a recent startup that's developed an open smarthome appliation that currently supports 1,000 devices and 8,000 apps. SmartThings will now work under the auspices of Samsung's Open Innovation Center (OIC). SmartThings Founder and CEO Alex Hawkinson...
Oct. 29, 2014 09:00 AM EDT Reads: 3,861
What process has your provider undertaken to ensure that the cloud tenant will receive predictable performance and service? What was involved in the planning? Who owns and operates the data center? What technology is being used? How is it being supported? In his session at 14th Cloud Expo, Dave Weisbrot, Cloud Business Manager for QTS, will provide the attendees a look into what it takes to stand up and stand behind a highly available certified cloud IaaS.
Oct. 29, 2014 08:30 AM EDT Reads: 1,557
I'll be hosting an SAP HANA Cloud webinar at 11am eastern time, Wednesday, October 29. You can sign up now. Featured speakers will be Allan Adler, Managing Partner, Channel Cloud Consulting, and Thorsten Leiduck, VP ISVs & Digital Commerce, SAP. Attendees will learn about • Cloud economics, hybrid cloud strategy, market size and opportunity • Introduction to SAP HANA Cloud Platform and how to: - Build new next-generation applications - Extend on-premise solutions non-disruptively throu...
Oct. 28, 2014 11:45 PM EDT Reads: 1,500
SYS-CON Events announced today that Gigaom Research has been named "Media Sponsor" of SYS-CON's 15th International Cloud Expo®, which will take place on November 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Ashar Baig, Research Director, Cloud, at Gigaom Research, will also lead a Power Panel on the topic "Choosing the Right Cloud Option." Gigaom Research provides timely, in-depth analysis of emerging technologies for individual and corporate subscribers. Gigaom Research'...
Oct. 28, 2014 11:45 PM EDT Reads: 1,720
Join both SAP and Channel Cloud Consulting for our webcast and uncover how you can extend your reach to capture a piece of the US$17 billion cloud application services market with SAP. Learn about SAPs market-leading SAP HANA Cloud Platform and an exciting opportunity to join SAPs growing ecosystem of Application Development partners. When: October 29, 11:00am EST Speakers: Allan Adler, Managing Partner, Channel Cloud Consulting Thorsten Leiduck, Vice President ISVs & Digital Commerce, SAP
Oct. 28, 2014 09:00 PM EDT Reads: 1,369
Application Performance Management (APM) has been bred with all the right elements to give us the insights we need to see the health of our applications. Similar to your most trusted watch dog, it alerts us to anomalies when events occur, providing awareness to the environment that only they can observe. As enterprises embrace the DevOps philosophy, and the coalescence of the Development and Operations continues, I foresee the conditions ripening to foster innovative methods of making applicati...
Oct. 28, 2014 08:15 PM EDT Reads: 5,227
SYS-CON Events announced today that IBM is holding a Bluemix Developer Playground on November 5, 10:30 am to 5:30 pm at 15th Cloud Expo. 15th Cloud Expo, co-located with @ThingsExpo, Big Data Expo, and DevOps Summit is taking place Nov. 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. The labs, for developers of all levels, will highlight the ease of use of Bluemix, its services and functionality and provide short-term introductory projects that developers can complete betw...
Oct. 28, 2014 08:00 PM EDT Reads: 1,637
The Industrial Internet revolution is now underway, enabled by connected machines and billions of devices that communicate and collaborate. The massive amounts of Big Data requiring real-time analysis is flooding legacy IT systems and giving way to cloud environments that can handle the unpredictable workloads. Yet many barriers remain until we can fully realize the opportunities and benefits from the convergence of machines and devices with Big Data and the cloud, including interoperability, da...
Oct. 28, 2014 12:00 PM EDT Reads: 1,969
Software AG helps organizations transform into Digital Enterprises, so they can differentiate from competitors and better engage customers, partners and employees. Using the Software AG Suite, companies can close the gap between business and IT to create digital systems of differentiation that drive front-line agility. We offer four on-ramps to the Digital Enterprise: alignment through collaborative process analysis; transformation through portfolio management; agility through process automation...
Oct. 28, 2014 10:00 AM EDT Reads: 2,074
How do you know when a technology has become mainstream? A good clue may be when politicians start talking about it on the campaign trail and with mainstream media. David Cameron, the UK prime minister, was the latest, indicating that the world was now on “fast-forward” with the Internet of Things (IoT) ushering in the new industrial revolution. No mention of IoT targeted at the masses would be complete without the clichéd example of the communicating fridge. While it is easy to get caught up in...
Oct. 28, 2014 08:00 AM EDT Reads: 6,306