Packet loss is a measure of how efficiently data is transferred across a network. When packets are lost, they are required (in most cases) to be retransmitted. This adds latency to an application as it has to wait for this retransmitted packet to be re-sent.
This makes packet loss a major contributor to poor application performance and therefore has a direct correlation to user experience. Packet loss is typically caused by network congestion, but can also be caused by other factors such as faulty equipment.
Packet loss is measured as a percentage of packets lost with respect to packets sent.
Packet loss (%) = packets lost / packets sent
When an application uses TCP, the lost packet is resent. Applications, like Microsoft Word, are built on TCP as data loss on a document is critical. In streaming media applications utilising UDP such as video, a small amount of loss may go unnoticed, this is because the video will still play even if some of the packets are lost. Lost packets are not re-sent when using UDP.
Measuring loss is not trivial. In my 15 plus years dealings in network performance management I found best practice is to get a complete and independent view into packet loss.
Best practice to visualise packet loss is
- Complete view - measure it everywhere, monitor packet loss at every edge of the network including the data centre and the users locations.
- Independent view - don't rely on each application to report packet loss as every application will measure and present results in its own way and many applications will not report it at all. Have a single tool measuring loss in the same way across all apps and all network points. .
- Measure it constantly: Loss needs to be measured constantly as packet loss issues are typically intermittent. These results should be saved and easily accessible.
- Measure it frequently: You need to get down to user experience frequency, we recommend at least every minute but ideally every one second
- Overlay network usage: Since network congestions is the key cause of packet loss, its important to be able to see network utilisation alongside packet loss so a correlation between the two can be easily made.
At Sinefa, we have built a comprehensive network performance management solution which reports extensively and effectively on packet loss.