Welcome!

@BigDataExpo Authors: Pat Romanski, William Schmarzo, Elizabeth White, Liz McMillan, Roger Strukhoff

Related Topics: Microservices Expo, Java IoT, Linux Containers, Containers Expo Blog, @CloudExpo, @BigDataExpo, SDN Journal

Microservices Expo: Article

Understanding APM on the Network

TCP Window Size

In Part 6, we dove into the Nagle algorithm - perhaps (or hopefully) something you'll never see. In Part VII, we get back to "pure" network and TCP roots as we examine how the TCP receive window interacts with WAN links.

TCP Window Size
Each node participating in a TCP connection advertises its available buffer space using the TCP window size field. This value identifies the maximum amount of data a sender can transmit without receiving a window update via a TCP acknowledgement; in other words, this is the maximum number of "bytes in flight" - bytes that have been sent, are traversing the network, but remain unacknowledged. Once the sender has reached this limit and exhausted the receive window, the sender must stop and wait for a window update.

The sender transmits a full window then waits for window updates before continuing. As these window updates arrive, the sender advances the window and may transmit more data.

Long Fat Networks
High-speed, high-latency networks, sometimes referred to as Long Fat Networks (LFNs), can carry a lot of data. On these networks, small receive window sizes can limit throughput to a fraction of the available bandwidth. These two factors - bandwidth and latency - combine to influence the potential impact of a given TCP window size. LFNs networks make it possible - common, even - for a sender to transmit very fast (high bandwidth) an entire TCP window's worth of data, having then to wait until the packets reach the distant remote site (high latency) so that acknowledgements can be returned, informing the sender of successful data delivery and available receive buffer space.

The math (and physics) concepts are straightforward. As the network speed increases, data can be clocked out onto the network medium more quickly; the bits are literally closer together. As latency increases, these bits take longer to traverse the network from sender to receiver. As a result, more bits can fit on the wire. As LFNs become more common, exhausting a receiver's TCP window becomes increasingly problematic for some types of applications.

Bandwidth Delay Product
The Bandwidth Delay Product (BDP) is a simple formula used to calculate the maximum amount of data that can exist on the network (referred to as bits or bytes in flight) based on a link's characteristics:

  • Bandwidth (bps) x RTT (seconds) = bits in flight
  • Divide the result by 8 for bytes in flight

If the BDP (in bytes) for a given network link exceeds the value of a session's TCP window, then the TCP session will not be able to use all of the available bandwidth; instead, throughput will be limited by the receive window (assuming no other constraints, of course).

The BDP can also be used to calculate the maximum throughput ("bandwidth") of a TCP connection given a fixed receive window size:

  • Bandwidth = (window size *8)/RTT

In the not-too-distant past, the TCP window had a maximum value of 65535 bytes. While today's TCP implementations now generally include a TCP window scaling option that allows for negotiated window sizes to reach 1GB, many factors limit its practical utility. For example, firewalls, load balancers and server configurations may purposely disable the feature. The reality is that we often still need to pay attention to the TCP window size when considering the performance of applications that transfer large amounts of data, particularly on enterprise LFNs.

As an example, consider a company with offices in New York and San Francisco; they need to replicate a large database each night, and have secured a 20Mbps network connection with 85 milliseconds of round-trip delay. Our BDP calculation tells us that the BDP is 212,500 (20,000,000 x .085 *8); in other words, a single TCP connection would require a 212KB window in order to take advantage of all of the bandwidth. The BDP calculation also tells us that the configured TCP window size of 65535 will permit approximately 6Mbps throughput (65535*8/.085), less than 1/3 of the link's capacity.

A link's BDP and a receiver's TCP window size are two factors that help us to identify the potential throughput of an operation. The remaining factor is the operation itself, specifically the size of individual request or reply flows. Only flows that exceed the receiver's TCP window size will benefit from, or be impacted by, these TCP window size constraints. Two common scenarios help illustrate this. Let's say a user needs to transfer a 1GB file:

  • Using FTP (in stream mode) will cause the entire file to be sent in a single flow; this operation could be severely limited by the receive window.
  • Using SMB (at least older versions of the protocol) will cause the file to be sent in many smaller write commands, as SMB used to limit write messages to under 64KB; this operation would not be able to take advantage of a TCP receive window of greater than 64K. (Instead, the operation would more likely be limited by application turns and link latency; we discuss chattiness in Part 8.)

For more networking tips, 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.


@BigDataExpo Stories
SYS-CON Events announced today that Niagara Networks will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Niagara Networks offers the highest port-density systems, and the most complete Next-Generation Network Visibility systems including Network Packet Brokers, Bypass Switches, and Network TAPs.
SYS-CON Events announced today that Secure Channels will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. The bedrock of Secure Channels Technology is a uniquely modified and enhanced process based on superencipherment. Superencipherment is the process of encrypting an already encrypted message one or more times, either using the same or a different algorithm.
If you’re responsible for an application that depends on the data or functionality of various IoT endpoints – either sensors or devices – your brand reputation depends on the security, reliability, and compliance of its many integrated parts. If your application fails to deliver the expected business results, your customers and partners won't care if that failure stems from the code you developed or from a component that you integrated. What can you do to ensure that the endpoints work as expect...
So, you bought into the current machine learning craze and went on to collect millions/billions of records from this promising new data source. Now, what do you do with them? Too often, the abundance of data quickly turns into an abundance of problems. How do you extract that "magic essence" from your data without falling into the common pitfalls? In her session at @ThingsExpo, Natalia Ponomareva, Software Engineer at Google, provided tips on how to be successful in large scale machine learning...
In his general session at 18th Cloud Expo, Lee Atchison, Principal Cloud Architect and Advocate at New Relic, discussed cloud as a ‘better data center’ and how it adds new capacity (faster) and improves application availability (redundancy). The cloud is a ‘Dynamic Tool for Dynamic Apps’ and resource allocation is an integral part of your application architecture, so use only the resources you need and allocate /de-allocate resources on the fly.
Enterprise IT has been in the era of Hybrid Cloud for some time now. But it seems most conversations about Hybrid are focused on integrating AWS, Microsoft Azure, or Google ECM into existing on-premises systems. Where is all the Private Cloud? What do technology providers need to do to make their offerings more compelling? How should enterprise IT executives and buyers define their focus, needs, and roadmap, and communicate that clearly to the providers?
SYS-CON Events announced today that eCube Systems, a leading provider of middleware modernization, integration, and management solutions, will exhibit at @DevOpsSummit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. eCube Systems offers a family of middleware evolution products and services that maximize return on technology investment by leveraging existing technical equity to meet evolving business needs. ...
Using new techniques of information modeling, indexing, and processing, new cloud-based systems can support cloud-based workloads previously not possible for high-throughput insurance, banking, and case-based applications. In his session at 18th Cloud Expo, John Newton, CTO, Founder and Chairman of Alfresco, described how to scale cloud-based content management repositories to store, manage, and retrieve billions of documents and related information with fast and linear scalability. He addres...
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management solutions, helping companies worldwide activate their data to drive more value and business insight and to transform moder...
The many IoT deployments around the world are busy integrating smart devices and sensors into their enterprise IT infrastructures. Yet all of this technology – and there are an amazing number of choices – is of no use without the software to gather, communicate, and analyze the new data flows. Without software, there is no IT. In this power panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists will look at the protocols that communicate data and the emerging data analy...
Digital innovation is the next big wave of business transformation based on digital technologies of which IoT and Big Data are key components, For example: Business boundary innovation is a challenge to excavate third-party business value using IoT and BigData, like Nest Business structure innovation may propose re-building business structure from scratch, as Uber does in the taxicab industry The social model innovation is also a big challenge to the new social architecture with the design fr...
Data is an unusual currency; it is not restricted by the same transactional limitations as money or people. In fact, the more that you leverage your data across multiple business use cases, the more valuable it becomes to the organization. And the same can be said about the organization’s analytics. In his session at 19th Cloud Expo, Bill Schmarzo, CTO for the Big Data Practice at EMC, will introduce a methodology for capturing, enriching and sharing data (and analytics) across the organizati...
There is little doubt that Big Data solutions will have an increasing role in the Enterprise IT mainstream over time. Big Data at Cloud Expo - to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA - has announced its Call for Papers is open. Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is...
SYS-CON Events announced today that Tintri Inc., a leading producer of VM-aware storage (VAS) for virtualization and cloud environments, will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Tintri VM-aware storage is the simplest for virtualized applications and cloud. Organizations including GE, Toyota, United Healthcare, NASA and 6 of the Fortune 15 have said “No to LUNs.” With Tintri they mana...
Creating replica copies to tolerate a certain number of failures is easy, but very expensive at cloud-scale. Conventional RAID has lower overhead, but it is limited in the number of failures it can tolerate. And the management is like herding cats (overseeing capacity, rebuilds, migrations, and degraded performance). Download Slide Deck: ▸ Here In his general session at 18th Cloud Expo, Scott Cleland, Senior Director of Product Marketing for the HGST Cloud Infrastructure Business Unit, discusse...
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with the 19th International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world and ThingsExpo Silicon Valley Call for Papers is now open.
SYS-CON Events has announced today that Roger Strukhoff has been named conference chair of Cloud Expo and @ThingsExpo 2016 Silicon Valley. The 19th Cloud Expo and 6th @ThingsExpo will take place on November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. "The Internet of Things brings trillions of dollars of opportunity to developers and enterprise IT, no matter how you measure it," stated Roger Strukhoff. "More importantly, it leverages the power of devices and the Interne...
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, provided an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life sett...
"My role is working with customers, helping them go through this digital transformation. I spend a lot of time talking to banks, big industries, manufacturers working through how they are integrating and transforming their IT platforms and moving them forward," explained William Morrish, General Manager Product Sales at Interoute, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
“We're a global managed hosting provider. Our core customer set is a U.S.-based customer that is looking to go global,” explained Adam Rogers, Managing Director at ANEXIA, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.