The ICA Session Latency report provides insight into the amount of session latency users might be experiencing. This report can be grouped by users or devices, as described in the sections that follow.

Prerequisites

Collection of the metrics in this report requires a minimum of the following component versions:

• EdgeSight 4.5 Agent running on the XenApp server
• Citrix Presentation Server 4.0 or 4.5, Advanced or Standard Edition

Overview

You can use this report to isolate any application servers experiencing latency. If users complain a specific application is slow, run this report with the name of the application servers' group specified as the Group and group the report by Device, User.

Some experts recommend aiming to keep latency for a user session under 150 kbit and note that a Citrix user session requires approximately 20kbits.

Note: ICA session latency only pertains to Presentation Server 4.0 or 4.5 (Standard and Advanced Editions only).

Counters

• Peak Latency (ms)
• Avg Latency (ms)

Interpreting the Data

The following provides a suggested process for interpreting the data and isolating the cause of the latency. 

To begin interpreting this report

1. Look for any outlying data points for users or devices. For example, if the report is grouped primarily by users, any users with double the session latency, such as "JaneS" and "MikeT" in the screen capture above. In this screen capture, the Peak Latency for "JaneS" is over ten times the Peak Latency of other users. In this report, the summary value for Peak Latency is the highest value reached ever; it is not an average of the Peak Latency for all sessions. However, the summary value for the Average Latency is an average of the average latency reported for each session.
2. Expand the outlying data point for more detail.  
3. Compare the Peak Latency with the Avg Latency. Is the user experiencing latency all the time or only at certain times?
4. Compare the individual sessions to each other. Is there one session that has more latency than the others? If so, where any events or upgrades occurring on the network? What about that application server's group? Was that server overloaded? To investigate server and farm health, see
5. (Optional.) If there was one server with more latency than the others, rerun the ICA Session Latency report grouped by Device, then User. Specify the name of the application server where the user experienced latency in the optional parameters.
6. (Optional.) Consider rerunning this report grouped by Hour if you are trying to correlate the latency against network events, such as outages or upgrades.

After reviewing this data, run the following reports determine if the latency is prominent on a particular virtual channel.

Start by running one of the ICA I/O reports (ICA Audio I/O, ICA Audio I/O) for the most likely candidate. The application server where the latency occurred might indicate where to start. For example, if the server hosts a Web browser, consider starting with the ICA Video I/O or the ICA Audio I/O report. If the server hosts a graphics aplication or Word processing application, consider starting with the ICA Printer I/O.

When you run these reports, group the report first by device and specify the application server's name as an Optional Parameter.

When you determine the channel on whihc the latency is occurring, run the ICA Session Compression report to see how effectively the XenApp is compressing session data. If ICA Session Compression Output (%) is significantly less than the ICA Session Compression Input (%), then TBD - xxx.

You can also use the ICA Session Monitoring and Control (SMC) portion of the Citrix Server Software Development Kit (SDK) to test the impact of restricting bandwidth on specific channels.

Suggested Resolutions

This section alludes to potential causes of latency and points to resources for resolution.

Causes of Latency

There are a variety of reasons for latency in sessions, including:

• Incorrect application scalability or excessive numbers of users connecting to the application server -- see
  • Outage of another server in a load managed group
• Network bandwidth issues
  • Excessive bandwidth devoted to printing - see
• Incorrect or suboptimal network design: the data store should be on the same subnet as most of the XenApp servers to minimize network traffic, file servers should be peer nodes in the same subnet as the farm servers. Also, consider teaming network cards in servers that initiate and maintain sessions, such as the Web Interface.

Suggested Resolutions

• Consider whether you can disable features that consume a lot of bandwidth, such as audio and multimedia.
• Session latency can also be improved by enabling features such as the SpeedScreen Acceleration features, Heavyweight Compression, SpeedScreen Latency Reduction, ICA Display, and ICA Browser. See the Citrix XenApp Administrator's Guide. Using mandatory profiles can help reduce latency.

In some cases, low bandwidth leads to session timeouts. You can mitigate this issue by ensuring the Session Reliability, Auto Client Reconnect, and ICA Keep Alive features are enabled.

Applicable Versions

EdgeSight 5.4
EdgeSight 5.3
EdgeSight 5.2
EdgeSight 5.1
EdgeSight 5.0

References

See Also

• Citrix Knowledge Center Support Forum post, "ICA session latency." Accessed on June 1, 2009.