Welcome!

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

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
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 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 ...

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

"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...
"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 ...
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...
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...
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...
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...
“In the past year we've seen a lot of stabilization of WebRTC. You can now use it in production with a far greater degree of certainty. A lot of the real developments in the past year have been in things like the data channel, which will enable a whole new type of application," explained Peter Dunkley, Technical Director at Acision, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
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...
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 cloud is becoming the de-facto way for enterprises to leverage common infrastructure while innovating and one of the biggest obstacles facing public cloud computing is security. In his session at 15th Cloud Expo, Jeff Aliber, a global marketing executive at Verizon, discussed how the best place for web security is in the cloud. Benefits include: Functions as the first layer of defense Easy operation –CNAME change Implement an integrated solution Best architecture for addressing network-l...
“We help people build clusters, in the classical sense of the cluster. We help people put a full stack on top of every single one of those machines. We do the full bare metal install," explained Greg Bruno, Vice President of Engineering and co-founder of StackIQ, in this SYS-CON.tv interview at 15th Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
DevOps Summit 2015 New York, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that it is now accepting Keynote Proposals. 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...
“DevOps is really about the business. The business is under pressure today, competitively in the marketplace to respond to the expectations of the customer. The business is driving IT and the problem is that IT isn't responding fast enough," explained Mark Levy, Senior Product Marketing Manager at Serena Software, in this SYS-CON.tv interview at DevOps Summit, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Mobile commerce traffic is surpassing desktop, yet less than 20% of sales in the U.S. are mobile commerce sales. In his session at 15th Cloud Expo, Dan Franklin, Segment Manager, Commerce, at Verizon Digital Media Services, defined mobile devices and discussed how next generation means simplification. It means taking your digital content and turning it into instantly gratifying experiences.