Jim Pierson

Microsoft - Global Foundation Services - Performance team releases Visual Roundtrip Analyzer tool to MSDN
The release of VRTA to the Microsoft Developer Network download site puts GFS on the map as a contributor of tools to the global developer community. VRTA creator and program manager Jim Pierson: "With VRTA, developers and testers worldwide have the ability to analyze and understand performance issues with their applications and improve their performance. VRTA has been a popular internal tool for some time, with version 3, we dramatically improved it together with the MSG team to ready it for public use." VRTA is available on Microsoft Download Center.

About VRTA

"VRTA is a Microsoft internal tool that was originally conceived and prototyped by Jim Pierson late Dec 2002. The existing Netmon tool captured packets but did not have a user friendly display of HTML traffic. Doug Franklin wrote the original RTA parser (now the All Files tab) and Ron Oshima tested, hardened, and (honestly) rewrote Jim's VRTA prototype, wrapping it into a 24x7 test harness. This early version became the staple of the MSNperf team's ability to analyze performance for MSN and Windows Live. In mid 2008, Lucius Fleuchaus led the development of the much improved VRTA3 along with Jason He, Vinod Mangalpally, Ron, and Jim as PM. We are delighted to share this tool with the public and hope it will be helpful in improving many web site's performance. "

Below is an excerpt from the "How to Use VRTA".

How to use (VRTA) Visual-Round-Trip-Analyzer

The Visual-Round-Trip-Analyzer tool helps web developers and testers visualize the download of their page, identify best practices and changes that improve performance. The Round-Trip between the client and server(s) is the single biggest impact to web page performance – much greater than server response time. VRTA examines the communications protocol, identifying the causes of excessive round-trips, and recommending solutions.

Visualizing the page download accurately, as it really flows, is essential to performance analysis. For example, it's difficult to know which parts of the page are serial and which are downloading in parallel. VRTA shows the page loading in three dimensions; the vertical scale shows TCP ports opening from Client to Server, the horizontal is the page-load-time in seconds, and on each port the files loading are shown. The colored bars are the files; Red is HTML text, gold represents style sheets, tan represents JavaScript, and blue lines are images. In this example, a single port is opened first to load the (Red) HTML file, and then 2 more ports are opened. After the first (gold) style sheet files are loaded, more files (tan) JavaScript and (blue) images are loaded on the same ports.

VRTA sits on top of NetMon 3.2 which is also released publically for free. VRTA abstracts the use of Netmon so the user does not need to know the details of Netmon but can simply click to start/stop the capture. VRTA has three primary features 1) a main chart which displays http traffic in 3 dimensions, 2) an All Files view that shows critical measurements for each file loading, and 3) an Analysis report that indicates which file transfers are exceptions to best practice rules.

Getting started:

• Start VRTA by clicking on the Green Arrow.
• Load a web page for testing (note, it's easiest to analyze only a single task at a time.)
• Stop VRTA by clicking the Red stop button. (The Start button turned red.)
• Review the output from VRTA using the 4 tab reports

• Note: To make this job easier, it is recommended to look at one atomic user actions at a time. Start the capture, click on the page and wait for it to render; then stop the capture. Start a new capture before the next click.

The Main Chart:

There are three parts to the main chart; on top is the Port chart, in the middle is the Bandwidth chart, and last is the Potential versus Actual chart.

The Port chart shows the files of the web page loading. Horizontally is the time to load the page – in the sample below, 12 seconds. The vertical scale shows the TCP ports that are opened from the Client to the server domains. Each of the color bars is a file. Red is HTML, Gold are style sheets. Tan is Java scripts. Light blue is GIF, dark blue for JPG, and dark navy for SWF files.

Below the main port chart, the Bandwidth chart shows the cumulative bit rate across all of the ports used. On the left hand vertical scale are the Kbits per second. The Red line is the average across the whole download.

At the bottom of the main chart tab is the Actual versus Potential chart. Actual is the average Kbit per second rate, shown by the Yellow line. The Potential, based on the max Kbps rate seen, is shown in Green. The ratio between these two numbers (Actual/ Potential) gives the Bandwidth Efficiency Rate.

Our VRTA tool shows files loading on TCP ports that are kept open using Keep-Alives. This is the new standard since HTTP1.1 was defined. Reusing TCP ports reduces the number of Round-Trips between client and server.

Inside each of the files, we are showing information about the TCP connection time, the Time-To First Byte, and the volume of packet s received.

First packet – the very first packet of a file down load is often a TCP connection – Sync packet. If the port is already opened, then the first packet is the Get Request.

TCP – the server will respond to the Client's Sync packet with a Sync-Ack to confirm opening the TCP connection. The vertical Pink shading is indicating when that TCP packet arrived from the server.

TTFB – Time-To-First-Byte is the first packet arriving from the server after the client sends a Get request packet.

Response packets – we are showing the volume of packets arriving from the server. TCP Slow start causes the server to send a few packets first, and then send more after the client acknowledges these. The server will 'ramp up' how many packets it sends per round-trip as long as the response times of the Client's Acks do not arrive slower at the server.

Hover over the files to see a drill down view into the details.

The All-Files tab:

This report shows each file and request listed in sequence of download. Use the Copy/Past button to paste this report directly into an excel sheet for easy viewing and analysis.

The Analysis tab:

We have created several best practice analysis rules that will look through your web page download and evaluate how well the page performs according to these best practices.

The text for each rule explains what the rule is looking for and how we grade.

Mouse over each rule to see the files that are found by our analysis to be suspect.

Click on the Copy/Past Icon to paste a list of the best practices, grades, and the exception files.

Menu -> Options:

Buffer Size: Maximum size in Megabytes of the Netmon capture file.

Beacon Regular Expressions: Beacons are downloaded files that can be used as markers for Page-Load-Time. For example, the MSN home page calls a clear gif file when the page has rendered at the end user. VRTA will place triangle markers onto the main chart when these files are seen.

Alternative HTTP ports: Some sites are using ports other than 80 or 443. Enter the port number here for VRTA to recognize them as HTTP.

Known issues:

• SSL encryption is not handled by Netmon at this time.
• IPv6 is not handled by VRTA at this time
• Local Host captures where the browser and server are on the same machine will not produce network traffic and therefore will not be caught by Netmon and VRTA.