Correcting Network Packet Loss
When more and more video joins the network, and it is prioritized above data traffic, the data will begin to suffer from more congestion loss. That affects all productivity apps, and thus productivity suffers.
In my last post, I described how to detect network packet loss and promised to talk about several causes of packet loss and how to fix them. The examples I have all came from real networks where I, or someone at Netcraftsmen, was working with a customer. I've written blog posts about some of the problems and the resolution of each. However, I've not put all the information in one place, which I intend to address with this blog.
Enterprise Connect in March 2012
Related to the content of this post are my presentations at Enterprise Connect 2012, March 26-29, 2012. I am hosting How To Keep Video From Blowing Up Your Network, in which I’ll talk about running a real network and how to keep video traffic from impacting the other business applications and to identify when business applications are being impacted. It is related to the congestion topic below. The second session is Network Test Tools for Voice and Video, where I will lead a panel discussion on how to use tools to diagnose problems with voice and video applications. Finally, I will be participating in John Bartlett's session on QoS & Net Design for Converged Networks. This session is always well attended because it covers a wide range of topics. I talk about resilient network design during my part of the session. All of these presentations are related to the topics in this post.
The Impact of Packet Loss on TCP
I've written about the impact of packet loss on TCP in several prior blog posts:
* http://www.netcraftsmen.net/resources/blogs/rethinking-interface-error-reports.html
* http://www.netcraftsmen.net/resources/blogs/application-performance-troubleshooting.html
The Mathis equation is an excellent way to determine the estimated packet loss of a given path. You have to know the round trip latency between the source and destination as well as the packet loss on the path to determine the maximum goodput, which is the volume of delivered user data. A graph of the resulting goodput for three different round trip times (RTT) is very informative. At 1Gbps, there is not much impact at 0.00001% packet loss. But at any higher packet loss, there is a significant reduction in goodput. Path RTT also has a big impact on goodput, as you can see in the graphs below.
Video and voice do not use TCP, so the graphs don't apply to them, but when you have significant amounts of voice and video, the other business applications that are using TCP may be impacted, depending on how you've set up QoS and allocated bandwidth. (That's the topic of my first Enterprise Connect session.)
