Welcome!

AJAX & REA Authors: Scott Hirsch, Sandi Mappic, Esmeralda Swartz, David H Deans, Carmen Gonzalez

Related Topics: SOA & WOA, Java, Linux, AJAX & REA, Web 2.0, Big Data Journal

SOA & WOA: Article

Understanding Application Performance on the Network | Part 3

TCP Slow-Start

In Part II, we discussed performance constraints caused by both bandwidth and congestion. Purposely omitted was a discussion about packet loss - which is often an inevitable result of heavy network congestion. I'll use this blog entry on TCP slow-start to introduce the Congestion Window (CWD), which is fundamental for Part IV's in-depth review of Packet Loss.

TCP Slow-Start
TCP uses a slow-start algorithm as it tries to understand the characteristics (bandwidth, latency, congestion) of the path supporting a new TCP connection. In most cases, TCP has no inherent understanding of the characteristics of the network path; it could be a switched connection on a high-speed LAN to a server in the next room, or it could be a low-bandwidth, already congested connection to a server halfway around the globe. In an effort to be a good network citizen, TCP uses a slow-start algorithm based on an internally-maintained congestion window (CWD) which identifies how many packets may be transmitted without being acknowledged; as the data carried in transmitted packets is acknowledged, the window increases. The CWD typically begins at two packets, allowing an initial transmission of two packets and then ramping up quickly as acknowledgements are received.

At the beginning of a new TCP connection, the CWD starts at two packets and increases as acknowledgements are received.

The CWD will continue to increase until one of three conditions is met:

Condition

Determined by

Blog discussion

Receiver's TCP Window limit

Receiver's TCP Window size

Part VII

Congestion detected (via packet loss)

Triple Duplicate ACK

Part IV

Maximum write block size

Application configuration

Part VIII

Generally, TCP slow-start will not be a primary or significant bottleneck. Slow-start occurs once per TCP connection, so for many operations there may be no impact. However, we will address the theoretical case of a TCP slow-start bottleneck, some influencing factors, and then present a real-world case.

The Maximum Segment Size and the CWD
The Maximum Segment Size (MSS) identifies the maximum TCP payload that can be carried by a packet; this value is set as a TCP option as a new connection is established. Probably the most common MSS value is 1460, but smaller sizes may be used to allow for VPN headers or to support different link protocols. Beyond the additional protocol overhead introduced by a reduced MSS, there is also an impact on the CWD, since the algorithm uses packets as its flow control metric.

We can consider the CWD's exchanges of data packets and subsequent ACKs as TCP turns, or TCP round trips; each exchange incurs the round-trip path delay. Therefore, one of the primary factors influencing the impact of TCP slow-start is network latency. A smaller MSS value will result in a larger number of packets - and additional TCP turns - as the sending node increases the CWD to reach its upper limit. It is possible that with a small MSS (536 Bytes) and high path delay (200 msec) that slow-start might introduce 3 seconds of delay to an operation as the CWD increases to a receive window limit of 65KB.

How Important Is TCP Slow-Start?
While significant, even a 3-second delay is probably not interesting for large file transfers, or for applications that reuse TCP connections. But let's consider a simple web page with 20 page elements, averaging about 120KB in size. A misconfigured proxy server prevents persistent TCP connections, so we'll need 20 new TCP connections to load the page. Each connection must ramp up through slow-start as content is downloaded. With a small MSS and/or high latency, each page component will experience a significant slow-start delay.

For more network performance insight from 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
Compute virtualization has been transformational, yet security policy implementation and enforcement has lagged behind in agility and automation. There are a number of key considerations when implementing policy in private and hybrid clouds. In his session at 15th Cloud Expo, Holland Barry, VP of Technology at Catbird, will discuss the impact of this new paradigm and what organizations can do today to safely move to software-defined network and compute architectures, including: How normal ope...
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...
How do APIs and IoT relate? The answer is not as simple as merely adding an API on top of a dumb device, but rather about understanding the architectural patterns for implementing an IoT fabric. There are typically two or three trends: Exposing the device to a management framework Exposing that management framework to a business centric logic • Exposing that business layer and data to end users. This last trend is the IoT stack, which involves a new shift in the separation of what stuff hap...
SYS-CON Events announced today that SOA Software, an API management leader, will exhibit at 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. SOA Software is a leading provider of API Management and SOA Governance products that equip business to deliver APIs and SOA together to drive their company to meet its business strategy quickly and effectively. SOA Software’s technology helps businesses to accel...
SYS-CON Events announced today that Utimaco will exhibit at 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. Utimaco is a leading manufacturer of hardware based security solutions that provide the root of trust to keep cryptographic keys safe, secure critical digital infrastructures and protect high value data assets. Only Utimaco delivers a general-purpose hardware security module (HSM) as a customiz...
Almost everyone sees the potential of Internet of Things but how can businesses truly unlock that potential. The key will be in the ability to discover business insight in the midst of an ocean of Big Data generated from billions of embedded devices via Systems of Discover. Businesses will also need to ensure that they can sustain that insight by leveraging the cloud for global reach, scale and elasticity.
SYS-CON Events announced today that ElasticBox is holding a Hackathon at DevOps Summit, November 6 from 12 pm -4 pm at the Santa Clara Convention Center in Santa Clara, CA. You can enter as an individual or team of up to 10 developers. A New Star Is Born Every Month! All completed ElasticBoxes will then be sent to a judging panel - 12 winners will be featured on the ElasticBox website in 2015. All entrants will receive five full enterprise licenses for one year + ElasticBox headphones + Elasti...
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 tranformation? In his session at 15th Cloud Expo, John Hatem, head of V...
Cloud services are the newest tool in the arsenal of IT products in the market today. These cloud services integrate process and tools. In order to use these products effectively, organizations must have a good understanding of themselves and their business requirements. In his session at 15th Cloud Expo, Brian Lewis, Principal Architect at Verizon Cloud, will outline key areas of organizational focus, and how to formalize an actionable plan when migrating applications and internal services to...
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 ...
Ixia develops amazing products so its customers can connect the world. Ixia helps its customers provide an always-on user experience through fast, secure delivery of dynamic connected technologies and services. Through actionable insights that accelerate and secure application and service delivery, Ixia's customers benefit from faster time to market, optimized application performance and higher-quality deployments.
SYS-CON Events announced today that Calm.io has been named “Bronze Sponsor” of DevOps Summit Silicon Valley, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Calm.io is a cloud orchestration platform for AWS, vCenter, OpenStack, or bare metal, that runs your CL tools puppet, Chef, shell, git, Jenkins, nagios, and will soon support New Relic and Docker. It can run hosted, or on premise and provides VM automation / expiry, self-service portals,...
In her General Session at 15th Cloud Expo, Anne Plese, Senior Consultant, Cloud Product Marketing, at Verizon Enterprise, will focus on finding the right mix of renting vs. buying Oracle capacity to scale to meet business demands, and offer validated Oracle database TCO models for Oracle development and testing environments. Anne Plese is a marketing and technology enthusiast/realist with over 19+ years in high tech. At Verizon Enterprise, she focuses on driving growth for the Verizon Cloud pla...
SYS-CON Events announced today that Aria Systems, the recurring revenue expert, 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. Aria Systems helps leading businesses connect their customers with the products and services they love. Industry leaders like Pitney Bowes, Experian, AAA NCNU, VMware, HootSuite and many others choose Aria to power their recurring revenue bu...
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...
As Platform as a Service (PaaS) matures as a category, developers should have the ability to use the programming language of their choice to build applications and have access to a wide array of services. Bluemix is IBM's open cloud development platform that enables users to easily build cloud-based, creative mobile and web applications without having to spend large amounts of time and resources on configuring infrastructure and multiple software licenses. In this track, you will learn about the...
Blue Box has closed a $10 million Series B financing. The round was led by a strategic investor and included participation from prior investors including Voyager Capital and Founders Collective, as well as the Blue Box executive team. This round follows a $4.3 million Series A closed in December of 2012 and led by Voyager Capital. In May of this year, the company announced general availability of its private cloud as a service offering, Blue Box Cloud. Since that release, the company has dem...
SYS-CON Events announced today that Verizon has been named "Gold 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. Verizon Enterprise Solutions creates global connections that generate growth, drive business innovation and move society forward. With industry-specific solutions and a full range of global wholesale offerings provided over the company's secure mobility, cloud, strategic network...
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...
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...