Question: Why am I seeing some sessions with high ICA and/or Network Latency but low ICA RTT?
Answer: ICA Latency should always be lower than ICA RTT. It should ideally be around half of the value of RTT. In some cases, it can be similar to the value of RTT but should never be higher.
ICA Latency is the time from when a user executes a keystroke or mouse click to when it is processed on the session host. It includes both network latency and any delay on the session host to process this request.
ICA Round Trip Time (RTT) is the elapsed time from when the user hits a key until the response is displayed back at the end point, as calculated by the session experience monitoring service.
ICA Latency is implemented by Citrix as a Windows Perfmon metric, and the default collection rate is proximately every 2 .5 +- mins for a new data point.
ICA RTT and Network Latency is implemented by Citrix as part of the EUE metrics, and the default collection rate is approximately every 50 +- secs for a new data point, or about 3x as frequent as ICA Latency.
The discrepancy in the session can be explained for a few reason:
- They are collected asynchronous to one another and on a different rate,
- Since they are produced by Citrix using different mechanisms (Perfmon vs. EUE), there could be lag between them.
- It is possible that short duration spikes (several seconds) in-between the collection are are missed in one metric relatively to the other, and vice-versa.
- As a result, it is more important to view these relative to one another as an average of multiple data-points for each over a period of multiple minutes.