When users complain that they are experiencing slowness in their VDIs, there are some points to check within in citrix.
If you have Citrix ADM (Application Delivery Management) installed and configured, you should see users sessions and bandwidth details in ADM. You may see high ICA RTT even though users say that they have very good internet plan. They always try to download a file or stream a YouTube video in HD and say, my internet is good. VDI has issue. It is slow.
Lets see what factors contribute to ICA RTT. Citrix Article, CTX204274 says:
- Client OS introduced delay – Client OS meaning – Operating System in user’s physical laptop/ personal laptops/ipad/Mobile etc ie., Device OS where user is connecting from.
- Client to NS introduced network delay(Wan Latency) – User’s physical laptop/ personal laptops to Netscaler.
- NS introduced delay in processing client to NS traffic(Client Side Device Latency) – It is Netscaler processing traffic, it may show as high if Netscaler is running on high cpu and memory. Because Netscaler is the one that processes it. If Netscaler is running at normal resource utilization, it shows correct value.
- NS introduced delay in processing NS to Server (XA/XD) traffic (Server Side Device Latency) – Self explanatory
- NS to Server network delay(DC Latency) – Self explanatory
- Server (XA/XD) OS introduced delay (Host Delay) – Self explanatory
DC stands for DataCenter. DC latency consists of all the switches/routers/firewalls etc that traffic goes through to get from the VDI to the internet.
From Citrix blog, How-network-latency-impacts-user-experience average network latency values are:
- Up to 150ms: great user experience
- 150ms – 300ms: good/acceptable user experience
- Over 300ms: degraded user experience
Some more details from Docs.citrix.com site:
|# Active Sessions||This number indicates the count of active Citrix Virtual Apps and Desktops sessions.|
|# Active Apps||This number indicates the count of active Citrix Virtual App sessions.|
|ICA RTT||ICA RTT is the screen lag that the user experiences while interacting with an application or desktop hosted on Citrix Virtual App or Desktop respectively.|
|WAN latency||Latency caused by the client side of the network. That is, from Citrix ADC to end user.|
|DC latency||Latency caused by the server side of the network. That is, from Citrix ADC to backend servers.|
|Bandwidth||Total bytes per second taken for end to end communication during the selected time interval.|
|Server Side Retransmits||The number of packets retransmitted on the connection between Citrix ADC and backend server.|
|Client Side Retransmits||The number of packets retransmitted on the connection between Citrix ADC and the end user. A high value of this metric does not mean that the user experience will not be seamless but indicates high bandwidth utilization due to retransmits.|
|Client side fast RTO||Number of times the retransmission timeout occurred the connection between Citrix ADC and the end user.|
|Server side fast RTO||Number of times the retransmission timeout occurred on the connection between Citrix ADC and backend server.|
|Client side Zero Window size event||This counter indicates the number of times the client advertised a zero TCP window.|
|Server side Zero Window size event||This counter indicates the number of times the server advertised a zero TCP window.|