Advanced Analysis "Excessive latency measured"

Inevitably this flag is raised when the path under test includes one or more satellite links. When we use satellites for data communications, we are using geosynchronous satellites, which sit at a lofty 22,000 miles above the equator. To use a satellite, data must travel about 50,000 miles, which translates to about 260msec latency. But to go half way around the world, you only need to travel 12,000 miles.

The diagram shows a satellite transmitting to Earth 22,000 miles away (275-375ms) versus the time to transmit half way around the Earth - 12,000 miles (< 250ms).

Symptoms of excessive latency:

  • File transfers usually are quick. Most other applications are slower.
  • Latency-bound applications become ridiculously slow.
  • TCP window issues are exacerbated.
  • Because of TCP window issues, on-demand links may never switch to high speed.

Performance issues to consider:

  • Some applications can handle high latency, but others fail.
  • Most applications are slower when using satellites. Degradation can be greatly increased based on how the application uses the network.
  • Typical degradation is 10 – 70%.