Welcome!

Microservices Expo Authors: Elizabeth White, Pat Romanski, Jason Bloomberg, Kong Yang, Mark Leake

Related Topics: Microservices Expo, Java IoT, Linux Containers, Containers Expo Blog, Machine Learning , @BigDataExpo

Microservices Expo: 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 Analytics at Dynatrace, responsible for DC RUM’s technical marketing programs. He is a co-inventor of multiple performance analysis features, and continues to champion the value of network performance analytics. He is the author of Network Application Performance Analysis (WalrusInk, 2014).

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.


@MicroservicesExpo Stories
Managing mission-critical SAP systems and landscapes has never been easy. Add public cloud with its myriad of powerful cloud native services and this may not change any time soon. Public cloud offers exciting new possibilities for enterprise workloads. But to make use of these possibilities and capabilities, IT teams need to re-think everything they have done before. Otherwise, they will just end up using public cloud as a hosting platform for their workloads, aka known as “lift and shift.”
You know you need the cloud, but you’re hesitant to simply dump everything at Amazon since you know that not all workloads are suitable for cloud. You know that you want the kind of ease of use and scalability that you get with public cloud, but your applications are architected in a way that makes the public cloud a non-starter. You’re looking at private cloud solutions based on hyperconverged infrastructure, but you’re concerned with the limits inherent in those technologies.
"Tintri focuses on the Ops side of the DevOps, which basically is pushing more and more of the accessibility of the infrastructure to the developers and trying to get behind the scenes," explained Dhiraj Sehgal of Tintri in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
Both SaaS vendors and SaaS buyers are going “all-in” to hyperscale IaaS platforms such as AWS, which is disrupting the SaaS value proposition. Why should the enterprise SaaS consumer pay for the SaaS service if their data is resident in adjacent AWS S3 buckets? If both SaaS sellers and buyers are using the same cloud tools, automation and pay-per-transaction model offered by IaaS platforms, then why not host the “shrink-wrapped” software in the customers’ cloud? Further, serverless computing, cl...
In the decade following his article, cloud computing further cemented Carr’s perspective. Compute, storage, and network resources have become simple utilities, available at the proverbial turn of the faucet. The value they provide is immense, but the cloud playing field is amazingly level. Carr’s quote above presaged the cloud to a T. Today, however, we’re in the digital era. Mark Andreesen’s ‘software is eating the world’ prognostication is coming to pass, as enterprises realize they must be...
Hybrid IT is today’s reality, and while its implementation may seem daunting at times, more and more organizations are migrating to the cloud. In fact, according to SolarWinds 2017 IT Trends Index: Portrait of a Hybrid IT Organization 95 percent of organizations have migrated crucial applications to the cloud in the past year. As such, it’s in every IT professional’s best interest to know what to expect.
A common misconception about the cloud is that one size fits all. Companies expecting to run all of their operations using one cloud solution or service must realize that doing so is akin to forcing the totality of their business functionality into a straightjacket. Unlocking the full potential of the cloud means embracing the multi-cloud future where businesses use their own cloud, and/or clouds from different vendors, to support separate functions or product groups. There is no single cloud so...
In 2014, Amazon announced a new form of compute called Lambda. We didn't know it at the time, but this represented a fundamental shift in what we expect from cloud computing. Now, all of the major cloud computing vendors want to take part in this disruptive technology. In his session at 20th Cloud Expo, Doug Vanderweide, an instructor at Linux Academy, discussed why major players like AWS, Microsoft Azure, IBM Bluemix, and Google Cloud Platform are all trying to sidestep VMs and containers wit...
Companies have always been concerned that traditional enterprise software is slow and complex to install, often disrupting critical and time-sensitive operations during roll-out. With the growing need to integrate new digital technologies into the enterprise to transform business processes, this concern has become even more pressing. A 2016 Panorama Consulting Solutions study revealed that enterprise resource planning (ERP) projects took an average of 21 months to install, with 57 percent of th...
The taxi industry never saw Uber coming. Startups are a threat to incumbents like never before, and a major enabler for startups is that they are instantly “cloud ready.” If innovation moves at the pace of IT, then your company is in trouble. Why? Because your data center will not keep up with frenetic pace AWS, Microsoft and Google are rolling out new capabilities. In his session at 20th Cloud Expo, Don Browning, VP of Cloud Architecture at Turner, posited that disruption is inevitable for comp...
New competitors, disruptive technologies, and growing expectations are pushing every business to both adopt and deliver new digital services. This ‘Digital Transformation’ demands rapid delivery and continuous iteration of new competitive services via multiple channels, which in turn demands new service delivery techniques – including DevOps. In this power panel at @DevOpsSummit 20th Cloud Expo, moderated by DevOps Conference Co-Chair Andi Mann, panelists examined how DevOps helps to meet the de...
"When we talk about cloud without compromise what we're talking about is that when people think about 'I need the flexibility of the cloud' - it's the ability to create applications and run them in a cloud environment that's far more flexible,” explained Matthew Finnie, CTO of Interoute, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
"We are a monitoring company. We work with Salesforce, BBC, and quite a few other big logos. We basically provide monitoring for them, structure for their cloud services and we fit into the DevOps world" explained David Gildeh, Co-founder and CEO of Outlyer, in this SYS-CON.tv interview at DevOps Summit at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
Colocation is a central pillar of modern enterprise infrastructure planning because it provides greater control, insight, and performance than managed platforms. In spite of the inexorable rise of the cloud, most businesses with extensive IT hardware requirements choose to host their infrastructure in colocation data centers. According to a recent IDC survey, more than half of the businesses questioned use colocation services, and the number is even higher among established businesses and busine...
For most organizations, the move to hybrid cloud is now a question of when, not if. Fully 82% of enterprises plan to have a hybrid cloud strategy this year, according to Infoholic Research. The worldwide hybrid cloud computing market is expected to grow about 34% annually over the next five years, reaching $241.13 billion by 2022. Companies are embracing hybrid cloud because of the many advantages it offers compared to relying on a single provider for all of their cloud needs. Hybrid offers bala...
@DevOpsSummit at Cloud Expo taking place Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center, Santa Clara, CA, is co-located with the 21st International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. 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 ...
The reality of data ubiquity is here—data is buried in operational statistics, machine logs, stacks of overflowing tickets and customer details, among other things. How can any user get valuable information amid this rapid influx of data? Imagine a situation where your firm’s revenue takes a hit owing to an unexpected failure in some business process. It would be a nightmare for IT admins to sift through the interminable piles of data to deduce exactly why and where the problem occurred. To sav...
For organizations that have amassed large sums of software complexity, taking a microservices approach is the first step toward DevOps and continuous improvement / development. Integrating system-level analysis with microservices makes it easier to change and add functionality to applications at any time without the increase of risk. Before you start big transformation projects or a cloud migration, make sure these changes won’t take down your entire organization.
What's the role of an IT self-service portal when you get to continuous delivery and Infrastructure as Code? This general session showed how to create the continuous delivery culture and eight accelerators for leading the change. Don Demcsak is a DevOps and Cloud Native Modernization Principal for Dell EMC based out of New Jersey. He is a former, long time, Microsoft Most Valuable Professional, specializing in building and architecting Application Delivery Pipelines for hybrid legacy, and cloud ...
21st International Cloud Expo, taking place October 31 - November 2, 2017, 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. Me...