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Dawn Parzych

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Top Stories by Dawn Parzych

TCP congestion control strives to optimize network goodput while minimizing packet loss by moderating transmission speed. Unfortunately, the way that congestion control moderates transmission often results in microbursts which can overflow buffers on switches and routers. This packet loss in turn triggers congestion control to moderate transmission speeds by reducing the congestion window; TCP then ramps up and the cycle repeats. This oscillation between under and over utilization of the network, combined with retransmission delays due to packet loss, cause application performance challenges and poor user experience. How does congestion control work? TCP moderates its transmission speed by calculating a target number of packets to keep in flight. This is the congestion window (cwnd). Typically, the congestion window starts out small and is increased each time the re... (more)

Bing Vs Google - A Performance Perspective

Being the total acceleration junkie that I am the first time a new site is launched or recommended to me the first thing I do is take a look at the performance of it.  So when I heard about Bing the first thing I did was fire up HttpWatch and take a look at the site.  To make things a little more interesting I decided to compare the results to Google, I used the classic home page and not my customized iGoogle home page. Tests were conducted from my home broadband connection in London, England.  Each test was done with a fresh instance of the browser and with an empty browser cac... (more)

A Brief History of TCP

The foundation of the Internet is TCP, it includes the rules for formatting messages, handling congestion, error correction and provides information on where a packet should be delivered, whether it arrived too quickly for the receiving computer and whether it arrived at all. Basically TCP is the glue that ensures network conditions work smoothly. As the way people connect to the internet has changed from 2400 baud modems to high speed fiber to the home and mobile connectivity – TCP is being stretched to perform optimally across multiple channels. It seems like for many years dev... (more)

What are you waiting for?

The future of HTTP is here, or almost here.   It has been 5 years since SPDY was first introduced as a better way to deliver web sites.  A lot has happened since then.  Chrome, Firefox, Opera and some IE installations support SPDY. SPDY evolved from v2 to v3 to v3.1. Sites like Google, Facebook, Twitter, and Wordpress to name just a few are available via SPDY. F5 announced availability of a SPDY Gateway. The IETF HTTP working group announced SPDY is the starting point for HTTP/2. And most recently - Apple has announced that Safari 8, due out this fall,  will support SPDY!  This ... (more)

v10 WebAccelerator and iRules

A customer recently contacted me regarding an iRule that worked in v 9.4 but did not produce the expected results in v 10.  A little research revealed that the new plug-in architecture is influencing when the iRule is firing. The iRule The iRule is logging the value of the X-PvInfo header or indicating the header is not present.  when HTTP_RESPONSE {   if {[HTTP::header exists X-PvInfo]}{    log local0. "X-PvInfo:[HTTP::header "X-PvInfo"]"   } else {    log local0. "did not find X-PvInfo header"   } } The Problem WebAccelerator inserts the X-PvInfo header into each and every respons... (more)