|By Gary Kaiser||
|August 16, 2014 04:00 PM EDT||
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.
Modern Systems announced completion of a successful project with its new Rapid Program Modernization (eavRPMa"c) software. The eavRPMa"c technology architecturally transforms legacy applications, enabling faster feature development and reducing time-to-market for critical software updates. Working with Modern Systems, the University of California at Santa Barbara (UCSB) leveraged eavRPMa"c to transform its Student Information System from Software AG's Natural syntax to a modern application lev...
Apr. 27, 2015 12:15 PM EDT Reads: 1,785
Chuck Piluso will present a study of cloud adoption trends and the power and flexibility of IBM Power and Pureflex cloud solutions. Speaker Bio: Prior to Data Storage Corporation (DSC), Mr. Piluso founded North American Telecommunication Corporation, a facilities-based Competitive Local Exchange Carrier licensed by the Public Service Commission in 10 states, serving as the company's chairman and president from 1997 to 2000. Between 1990 and 1997, Mr. Piluso served as chairman & founder of ...
Apr. 27, 2015 12:00 PM EDT
There is no quick way to learn Jython API but to experiment with it. The easiest way is to start with Jytutor extension for XL Deploy. Now you can also use the code snippet for exposing jython/python context in XL Deploy environment by running it directly in Jytutor Here’s how you can go ahead with that Download the Jytutor extension referring to the Jytutor Blog or from the following link https://github.com/xebialabs-community/xld-jytutor-plugin/releases Shutdown your XL Deploy server...
Apr. 27, 2015 12:00 PM EDT Reads: 889
ProfitBricks has launched its new DevOps Central and REST API, along with support for three multi-cloud libraries and a Python SDK. This, combined with its already existing SOAP API and its new RESTful API, moves ProfitBricks into a position to better serve the DevOps community and provide the ability to automate cloud infrastructure in a multi-cloud world. Following this momentum, ProfitBricks has also introduced several libraries that enable developers to use their favorite language to code ...
Apr. 27, 2015 12:00 PM EDT Reads: 1,708
ProfitBricks, the provider of painless cloud infrastructure IaaS, announced the launch of its new DevOps Central and REST API, along with support for three multi-cloud libraries and a Python SDK. This, combined with its already existing SOAP API and its new RESTful API, moves ProfitBricks into a position to better serve the DevOps community and provide the ability to automate cloud infrastructure in a multi-cloud world. Following this momentum, ProfitBricks is also today introducing several l...
Apr. 27, 2015 12:00 PM EDT Reads: 1,201
The 17th International Cloud Expo has announced that its Call for Papers is open. 17th International Cloud Expo, to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, APM, APIs, Microservices, Security, Big Data, Internet of Things, DevOps and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding bu...
Apr. 27, 2015 12:00 PM EDT Reads: 2,329
Security is one the more prominent of the application service categories, likely due to its high profile impact. After all, if security fails, we all hear about it. The entire Internet. Forever. So when one conducts a survey on the state of application delivery (which is implemented using application services) you kinda have to include security. Which of course, we did.
Apr. 27, 2015 11:30 AM EDT Reads: 2,029
Chef and Canonical announced a partnership to integrate and distribute Chef with Ubuntu. Canonical is integrating the Chef automation platform with Canonical's Machine-As-A-Service (MAAS), enabling users to automate the provisioning, configuration and deployment of bare metal compute resources in the data center. Canonical is packaging Chef 12 server in upcoming distributions of its Ubuntu open source operating system and will provide commercial support for Chef within its user base.
Apr. 27, 2015 11:00 AM EDT Reads: 1,870
In 2015, 4.9 billion connected "things" will be in use. By 2020, Gartner forecasts this amount to be 25 billion, a 410 percent increase in just five years. How will businesses handle this rapid growth of data? Hadoop will continue to improve its technology to meet business demands, by enabling businesses to access/analyze data in real time, when and where they need it. Cloudera's Chief Technologist, Eli Collins, will discuss how Big Data is keeping up with today's data demands and how in t...
Apr. 27, 2015 11:00 AM EDT Reads: 1,478
SYS-CON Events announced today that MangoApps 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., and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. MangoApps provides private all-in-one social intranets allowing workers to securely collaborate from anywhere in the world and from any device. Social, mobile, and eas...
Apr. 27, 2015 11:00 AM EDT Reads: 3,591
Choosing between BIG-IP and LineRate isn't as difficult as it seems.... Our recent announcement of the availability of LineRate Point raised the same question over and over: isn't this just a software-version of BIG-IP? How do I know when to choose LineRate Point instead of BIG-IP VE (Virtual Edition)? Aren't they the same?? No, no they aren't. LineRate Point (and really Line Rate Precision, too) is more akin to an app proxy while BIG-IP VE remains, of course, an ADC (Application Delivery ...
Apr. 27, 2015 11:00 AM EDT Reads: 1,035
SYS-CON Media announced today that @ThingsExpo Blog launched with 7,788 original stories. @ThingsExpo Blog offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. @ThingsExpo Blog can be bookmarked. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago.
Apr. 27, 2015 11:00 AM EDT Reads: 2,573
No, not the head-banging, gritty, heavy metal Metallica song (though that's certainly awesome too.. excuse me for a moment while I turn it up to 11) but the Puppet as in automation kind of master. The importance placed on APIs - which are key to automation - in our State of Application Delivery 2015 survey was high, with 40% of respondents saying it was important to them that their infrastructure be API-enabled. Automation using those APIs is generally being accomplished through a variety of m...
Apr. 27, 2015 11:00 AM EDT Reads: 1,534
Containers and microservices have become topics of intense interest throughout the cloud developer and enterprise IT communities. Accordingly, attendees at the upcoming 16th Cloud Expo at the Javits Center in New York June 9-11 will find fresh new content in a new track called PaaS | Containers & Microservices Containers are not being considered for the first time by the cloud community, but a current era of re-consideration has pushed them to the top of the cloud agenda. With the launch ...
Apr. 27, 2015 11:00 AM EDT Reads: 2,892
The world's leading Cloud event, Cloud Expo has launched Microservices Journal on the SYS-CON.com portal, featuring over 19,000 original articles, news stories, features, and blog entries. DevOps Journal is focused on this critical enterprise IT topic in the world of cloud computing. Microservices Journal offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. Follow new article posts on T...
Apr. 27, 2015 11:00 AM EDT Reads: 2,117
So I guess we’ve officially entered a new era of lean and mean. I say this with the announcement of Ubuntu Snappy Core, “designed for lightweight cloud container hosts running Docker and for smart devices,” according to Canonical. “Snappy Ubuntu Core is the smallest Ubuntu available, designed for security and efficiency in devices or on the cloud.” This first version of Snappy Ubuntu Core features secure app containment and Docker 1.6 (1.5 in main release), is available on public clouds, ...
Apr. 27, 2015 10:45 AM EDT Reads: 1,434
How do you securely enable access to your applications in AWS without exposing any attack surfaces? The answer is usually very complicated because application environments morph over time in response to growing requirements from your employee base, your partners and your customers. In his session at 16th Cloud Expo, Haseeb Budhani, CEO and Co-founder of Soha, will share five common approaches that DevOps teams follow to secure access to applications deployed in AWS, Azure, etc., and the frict...
Apr. 27, 2015 10:30 AM EDT Reads: 1,674
While DevOps most critically and famously fosters collaboration, communication, and integration through cultural change, culture is more of an output than an input. In order to actively drive cultural evolution, organizations must make substantial organizational and process changes, and adopt new technologies, to encourage a DevOps culture. Moderated by Andi Mann, panelists will discuss how to balance these three pillars of DevOps, where to focus attention (and resources), where organizations m...
Apr. 27, 2015 10:15 AM EDT Reads: 2,051
A few weeks ago, SmartBear hosted API Craft Boston with the folks from Akana, Ian Goldsmith and Laura Heritage, to talk about microservices. It was an extremely informative presentation of where microservices came from, what it solves, and considerations around how it might fit into an organizational API strategy. It’s one thing to read everyone else’s opinions on blogs, twitter, etc. It’s great to go to workshops and conferences, but this was so intelligently presented (and for a meetup too)...
Apr. 27, 2015 10:00 AM EDT Reads: 796
Buzzword alert: Microservices and IoT at a DevOps conference? What could possibly go wrong? Join this panel of experts as they peel away the buzz and discuss the important architectural principles behind implementing IoT solutions for the enterprise. As remote IoT devices and sensors become increasingly intelligent, they become part of our distributed cloud environment, and we must architect and code accordingly. At the very least, you’ll have no problem filling in your buzzword bingo cards.
Apr. 27, 2015 10:00 AM EDT Reads: 2,221