Welcome!

AJAX & REA Authors: Elizabeth White, Trevor Parsons, ChandraShekar Dattatreya, Liz McMillan, David H Deans

Related Topics: SOA & WOA, Java, Linux, Virtualization, AJAX & REA, Big Data Journal

SOA & WOA: Article

Understanding Application Performance on the Network | Part 2

Bandwidth and Congestion

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.

Bandwidth
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
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.

More Stories By Gary Kaiser

Gary Kaiser is a Subject Matter Expert in Network Performance Analysis at Compuware APM. He has global field enablement responsibilities for performance monitoring and analysis solutions embracing emerging and strategic technologies, including WAN optimization, thin client infrastructures, network forensics, and a unique performance management maturity methodology. He is also a co-inventor of multiple analysis features, and continues to champion the value of software-enabled expert network analysis.

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.


@CloudExpo Stories
Lori MacVittie is responsible for education and evangelism of application services available across F5's entire product suite. Her role includes authorship of technical materials and participation in a number of community-based forums and industry standards organizations, among other efforts. MacVittie has extensive programming experience as an application architect, as well as network and systems development and administration expertise. Prior to joining F5, MacVittie was an award-winning Senio...
ScriptRock makes GuardRail, a DevOps-ready platform for configuration monitoring. Realizing we were spending way too much time digging up, cataloguing, and tracking machine configurations, we began writing our own scripts and tools to handle what is normally an enormous chore. Then we took the concept a step further, giving it a beautiful interface and making it simple enough for our bosses to understand. We named it GuardRail after its function - to allow businesses to move fast and stay sa...
SYS-CON Media announced today that Skytap blog on "DevOps Journal" exceeded 84,000 story reads. DevOps Journal is focused on this critical enterprise IT topic in the world of cloud computing. DevOps Journal brings valuable information to DevOps professionals who are transforming the way enterprise IT is done. Noel Wurst is the managing content editor at Skytap. Skytap provides SaaS-based dev/test environments to the enterprise. Skytap solution removes the inefficiencies and constraints that comp...
SYS-CON Media announced today that Sematext launched a popular blog feed on DevOps Journal with over 6,000 story reads over the weekend. DevOps Journal is focused on this critical enterprise IT topic in the world of cloud computing. DevOps Journal brings valuable information to DevOps professionals who are transforming the way enterprise IT is done. Sematext is a globally distributed organization that builds innovative Cloud and On Premises solutions for performance monitoring, alerting an...
SYS-CON Events announced today Isomorphic Software, the global leader in high-end, web-based business applications, will exhibit at SYS-CON's DevOps Summit 2015 New York, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Isomorphic Software is the global leader in high-end, web-based business applications. We develop, market, and support the SmartClient & Smart GWT HTML5/Ajax platform, combining the productivity and performance of traditional desktop software ...
SYS-CON Events announced today that Cloudian, Inc., the leading provider of hybrid cloud storage solutions, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Cloudian, Inc., is a Foster City, California - based software company specializing in cloud storage software. The main product is Cloudian, an Amazon S3-compliant cloud object storage platform, the bedrock of cloud computing systems, that enables c...
Leysin American School is an exclusive, private boarding school located in Leysin, Switzerland. Leysin selected an OpenStack-powered, private cloud as a service to manage multiple applications and provide development environments for students across the institution. Seeking to meet rigid data sovereignty and data integrity requirements while offering flexible, on-demand cloud resources to users, Leysin identified OpenStack as the clear choice to round out the school's cloud strategy. Additional...
The BPM world is going through some evolution or changes where traditional business process management solutions really have nowhere to go in terms of development of the road map. In this demo at 15th Cloud Expo, Kyle Hansen, Director of Professional Services at AgilePoint, shows AgilePoint’s unique approach to dealing with this market circumstance by developing a rapid application composition or development framework.
SYS-CON Events announced today that Windstream, a leading provider of advanced network and cloud communications, has been named “Silver Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9–11, 2015, at the Javits Center in New York, NY. Windstream (Nasdaq: WIN), a FORTUNE 500 and S&P 500 company, is a leading provider of advanced network communications, including cloud computing and managed services, to businesses nationwide. The company also offers broadband, p...
In high-production environments where release cycles are measured in hours or minutes — not days or weeks — there's little room for mistakes and no room for confusion. Everyone has to understand what's happening, in real time, and have the means to do whatever is necessary to keep applications up and running optimally. DevOps is a high-stakes world, but done well, it delivers the agility and performance to significantly impact business competitiveness.
"Our premise is Docker is not enough. That's not a bad thing - we actually love Docker. At ActiveState all our products are based on open source technology and Docker is an up-and-coming piece of open source technology," explained Bart Copeland, President & CEO of ActiveState Software, in this SYS-CON.tv interview at DevOps Summit at Cloud Expo®, held Nov 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
The Internet of Things is not new. Historically, smart businesses have used its basic concept of leveraging data to drive better decision making and have capitalized on those insights to realize additional revenue opportunities. So, what has changed to make the Internet of Things one of the hottest topics in tech? In his session at @ThingsExpo, Chris Gray, Director, Embedded and Internet of Things, discussed the underlying factors that are driving the economics of intelligent systems. Discover ...
"BSQUARE is in the business of selling software solutions for smart connected devices. It's obvious that IoT has moved from being a technology to being a fundamental part of business, and in the last 18 months people have said let's figure out how to do it and let's put some focus on it, " explained Dave Wagstaff, VP & Chief Architect, at BSQUARE Corporation, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
The major cloud platforms defy a simple, side-by-side analysis. Each of the major IaaS public-cloud platforms offers their own unique strengths and functionality. Options for on-site private cloud are diverse as well, and must be designed and deployed while taking existing legacy architecture and infrastructure into account. Then the reality is that most enterprises are embarking on a hybrid cloud strategy and programs. In this Power Panel at 15th Cloud Expo (http://www.CloudComputingExpo.com...
Verizon Enterprise Solutions is simplifying the cloud-purchasing experience for its clients, with the launch of Verizon Cloud Marketplace, a key foundational component of the company's robust ecosystem of enterprise-class technologies. The online storefront will initially feature pre-built cloud-based services from AppDynamics, Hitachi Data Systems, Juniper Networks, PfSense and Tervela. Available globally to enterprises using Verizon Cloud, Verizon Cloud Marketplace provides a one-stop shop fo...
The move in recent years to cloud computing services and architectures has added significant pace to the application development and deployment environment. When enterprise IT can spin up large computing instances in just minutes, developers can also design and deploy in small time frames that were unimaginable a few years ago. The consequent move toward lean, agile, and fast development leads to the need for the development and operations sides to work very closely together. Thus, DevOps become...
SYS-CON Events announced today that IDenticard will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. IDenticard™ is the security division of Brady Corp (NYSE: BRC), a $1.5 billion manufacturer of identification products. We have small-company values with the strength and stability of a major corporation. IDenticard offers local sales, support and service to our customers across the United States and Canada...
SYS-CON Events announced today that AIC, a leading provider of OEM/ODM server and storage solutions, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. AIC is a leading provider of both standard OTS, off-the-shelf, and OEM/ODM server and storage solutions. With expert in-house design capabilities, validation, manufacturing and production, AIC's broad selection of products are highly flexible and are conf...

ARMONK, N.Y., Nov. 20, 2014 /PRNewswire/ --  IBM (NYSE: IBM) today announced that it is bringing a greater level of control, security and flexibility to cloud-based application development and delivery with a single-tenant version of Bluemix, IBM's

AppZero has announced that its award-winning application migration software is now fully qualified within the Microsoft Azure Certified program. AppZero has undergone extensive technical evaluation with Microsoft Corp., earning its designation as Microsoft Azure Certified. As a result of AppZero's work with Microsoft, customers are able to easily find, purchase and deploy AppZero from the Azure Marketplace. With just a few clicks, users have an Azure-based solution for moving applications to the...